I have a low power FM transmitter that I use for in my house and yard.
I want to put a 1/4 wave vertical on the roof of my home. The 1/4 wave
vertical will be made as many have seen from a UHF panel mount connector
with the vertical on the center pin and the four radials soldered to the
holes for the screws.
Like this,
https://encrypted-tbn1.gstatic.com/i...M00RrltFyCH-LA
Only bigger :-)

Looking at the pattern of a 1/4 wave vertical, I think I could best
cover my yard with the pattern upside down.

Can I mount the antenna upside down?

Is this feasible?

If I did turn it upside down, what would the feedline do to the pattern?

Is there a better physical layout to avoid pattern distortion caused
by the feedline?

Mikek

On Sat, 30 Nov 2013 21:42:38 -0600, amdx wrote:

I have a low power FM transmitter that I use for in my house and yard.
I want to put a 1/4 wave vertical on the roof of my home. The 1/4 wave
vertical will be made as many have seen from a UHF panel mount connector
with the vertical on the center pin and the four radials soldered to the
holes for the screws.
Like this,
https://encrypted-tbn1.gstatic.com/i...M00RrltFyCH-LA
Only bigger :-)

Unless you use stiff elements, they will sag. At 100MHz, 1/4
wavelength is about 75 cm (2.5 ft) long.

Looking at the pattern of a 1/4 wave vertical, I think I could best
cover my yard with the pattern upside down.

Think again please.

Can I mount the antenna upside down?

Yes.

Is this feasible?

Yes. It's commonly done with UHF antennas on mountain top sites.

If I did turn it upside down, what would the feedline do to the pattern?

The feed line will mangle the pattern.

Is there a better physical layout to avoid pattern distortion caused
by the feedline?

Yes. Use a vertical dipole on a tower or a coaxial antenna on a vent
pipe.

The alleged problem with a ground plane antenna is that there is a
slight vertical uptilt of the beam. It varies with the height above
the rooftop ground, but my guess(tm) is maybe 5 to 10 degrees uptilt.
I just ran a simple ground plane simulation using 4NEC2 and found that
the uptilt is small when the vertical beamwidth of the ground plane is
about 90 degrees. In other words, inverting the antenna isn't going
to do much good at delivering the signal towards the ground. You're
better off with an antenna that puts the main lobes where your
receiver is located or perhaps has some gain and/or downtilt. Without
a description of your house and yard, I can't offer any suggestions.
Numbers please?

You might find it useful to look at what the LPFM people are doing for
antennas:
https://www.google.com/search?q=lpfm+antenna&tbm=isch
Remember, the stranger it looks, the better it works.

Ummm... what problem are you trying to solve?

--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

On 11/30/2013 10:30 PM, Jeff Liebermann wrote:
On Sat, 30 Nov 2013 21:42:38 -0600, amdx wrote:

I have a low power FM transmitter that I use for in my house and yard.
I want to put a 1/4 wave vertical on the roof of my home. The 1/4 wave
vertical will be made as many have seen from a UHF panel mount connector
with the vertical on the center pin and the four radials soldered to the
holes for the screws.
Like this,
https://encrypted-tbn1.gstatic.com/i...M00RrltFyCH-LA
Only bigger :-)

Unless you use stiff elements, they will sag. At 100MHz, 1/4
wavelength is about 75 cm (2.5 ft) long.

Looking at the pattern of a 1/4 wave vertical, I think I could best
cover my yard with the pattern upside down.

Think again please.

I did, a couple times.
I wondered, how does the ground (the dirt) under the radial ground
affect the pattern?
Then I thought: The classic pattern is not exact, otherwise I'd get no
signal in my house with the antenna on the roof.
Also (I thinked) just changing from the 8" rubber ducky to the the 1/4
wave on the roof will make a huge difference.

Can I mount the antenna upside down?

Yes.
Will I knew I could! We have an upside down building not far from here.
The better question, is there a good reason to mount the antenna upside
down?

Is this feasible?

Yes. It's commonly done with UHF antennas on mountain top sites.

Darn, not an original idea!


If I did turn it upside down, what would the feedline do to the pattern?

The feed line will mangle the pattern.

So why did I ask, I knew that.


Is there a better physical layout to avoid pattern distortion caused
by the feedline?

Yes. Use a vertical dipole on a tower or a coaxial antenna on a vent
pipe.

Hmm, vertical dipole,
But, then I'd miss the excitement of paralleling 90* of two 75 ohm
coax cables and the measurements to match 37 ohms to 50 ohms. I wanted
to see that happen. I guess I could still do the experiment.

The alleged problem with a ground plane antenna is that there is a
slight vertical uptilt of the beam. It varies with the height above
the rooftop ground, but my guess(tm) is maybe 5 to 10 degrees uptilt.
I just ran a simple ground plane simulation using 4NEC2 and found that
the uptilt is small when the vertical beamwidth of the ground plane is
about 90 degrees. In other words, inverting the antenna isn't going
to do much good at delivering the signal towards the ground. You're
better off with an antenna that puts the main lobes where your
receiver is located or perhaps has some gain and/or downtilt. Without
a description of your house and yard, I can't offer any suggestions.
Numbers please?

Ok, as you might have guessed, a lot of this is, as a previous boss of
mine, used to call "mental masturbation"
I do intend to mount an antenna outside (again), now, I'm not sure
what type.
The problem I'm solving is, in some areas of my yard, the radio signal
gets buzzy, sometimes turning the radio will fix it, often I have to
move the radio 5ft to get a clear signal.
My transmitter is a CZH-05B, the power is switchable between 0.1 watt
and 0.5 watts. I run it at 0.1 watt in an effort to keep myself out of
trouble. Hmm, as I'm writing I noted I have two 3.0db attenuators before
the antenna, as more keep myself out of trouble units.
(Btw, I just modified a 13 element filter to put between the
transmitter and the antenna. Someday I hope to have the equipment to
analyze it and see how well it works ( how well I did). I started with a
TFD6102A and wound new coils and added capacitance as needed. I have not
installed it yet.) I recently bought an HP 141T/8553, if I find a 8555
at a reasonable price, I'll buy it.
The receive area is small, 120" x 115", the antenna will be mounted
13" in from the long dimension and 16" in from the smaller dimension,
basically in the corner of the lot, mounted 16 ft high.

Jeff, at this point, I have convinced myself putting a gain antenna on
the roof will solve any problem I may have. If not I can still remove
6db of attenuation. So unless you want some mental exercise, don't over
do it!
I think you suggested a vertical dipole with downtilt. Any thoughts
about matching, I have no clue how tolerant this little transmitter is.
Hmm, maybe put a 3db attenuator on the transmitter output, into the
LPF, then another 3db attenuator between the LPF and the antenna.
Then my transmitter's happy, and my filter is happy.


You might find it useful to look at what the LPFM people are doing for
antennas:
https://www.google.com/search?q=lpfm+antenna&tbm=isch
Remember, the stranger it looks, the better it works.

Ummm... what problem are you trying to solve?

Who said I have a problem? ;-)

I'll add, I have messed with the Ramsey FM transmitter and a couple of
others, This transmitter works great, and they're down to about $60 now,
half what I paid two years ago. The newer models go up to 7 watts,
if you can believe the specs.
I run my internet radio into the FM transmitter so I can listen to it
around the home.

Mikek

On 12/1/2013 10:49 AM, amdx wrote:
On 11/30/2013 10:30 PM, Jeff Liebermann wrote:
On Sat, 30 Nov 2013 21:42:38 -0600, amdx wrote:

I have a low power FM transmitter that I use for in my house and yard.
I want to put a 1/4 wave vertical on the roof of my home. The 1/4 wave
vertical will be made as many have seen from a UHF panel mount connector
with the vertical on the center pin and the four radials soldered to the
holes for the screws.
Like this,
https://encrypted-tbn1.gstatic.com/i...M00RrltFyCH-LA

Only bigger :-)

Unless you use stiff elements, they will sag. At 100MHz, 1/4
wavelength is about 75 cm (2.5 ft) long.

Looking at the pattern of a 1/4 wave vertical, I think I could best
cover my yard with the pattern upside down.

Think again please.

I did, a couple times.
I wondered, how does the ground (the dirt) under the radial ground
affect the pattern?
Then I thought: The classic pattern is not exact, otherwise I'd get no
signal in my house with the antenna on the roof.
Also (I thinked) just changing from the 8" rubber ducky to the the 1/4
wave on the roof will make a huge difference.

Can I mount the antenna upside down?

Yes.
Will I knew I could! We have an upside down building not far from here.
The better question, is there a good reason to mount the antenna upside
down?

Is this feasible?

Yes. It's commonly done with UHF antennas on mountain top sites.

Darn, not an original idea!


If I did turn it upside down, what would the feedline do to the pattern?

The feed line will mangle the pattern.

So why did I ask, I knew that.


Is there a better physical layout to avoid pattern distortion caused
by the feedline?

Yes. Use a vertical dipole on a tower or a coaxial antenna on a vent
pipe.

Hmm, vertical dipole,
But, then I'd miss the excitement of paralleling 90* of two 75 ohm
coax cables and the measurements to match 37 ohms to 50 ohms. I wanted
to see that happen. I guess I could still do the experiment.

The alleged problem with a ground plane antenna is that there is a
slight vertical uptilt of the beam. It varies with the height above
the rooftop ground, but my guess(tm) is maybe 5 to 10 degrees uptilt.
I just ran a simple ground plane simulation using 4NEC2 and found that
the uptilt is small when the vertical beamwidth of the ground plane is
about 90 degrees. In other words, inverting the antenna isn't going
to do much good at delivering the signal towards the ground. You're
better off with an antenna that puts the main lobes where your
receiver is located or perhaps has some gain and/or downtilt. Without
a description of your house and yard, I can't offer any suggestions.
Numbers please?

Ok, as you might have guessed, a lot of this is, as a previous boss of
mine, used to call "mental masturbation"
I do intend to mount an antenna outside (again), now, I'm not sure
what type.
The problem I'm solving is, in some areas of my yard, the radio signal
gets buzzy, sometimes turning the radio will fix it, often I have to
move the radio 5ft to get a clear signal.
My transmitter is a CZH-05B, the power is switchable between 0.1 watt
and 0.5 watts. I run it at 0.1 watt in an effort to keep myself out of
trouble. Hmm, as I'm writing I noted I have two 3.0db attenuators before
the antenna, as more keep myself out of trouble units.
(Btw, I just modified a 13 element filter to put between the
transmitter and the antenna. Someday I hope to have the equipment to
analyze it and see how well it works ( how well I did). I started with a
TFD6102A and wound new coils and added capacitance as needed. I have not
installed it yet.) I recently bought an HP 141T/8553, if I find a 8555
at a reasonable price, I'll buy it.
The receive area is small, 120" x 115", the antenna will be mounted
13" in from the long dimension and 16" in from the smaller dimension,
basically in the corner of the lot, mounted 16 ft high.

Jeff, at this point, I have convinced myself putting a gain antenna on
the roof will solve any problem I may have. If not I can still remove
6db of attenuation. So unless you want some mental exercise, don't over
do it!
I think you suggested a vertical dipole with downtilt. Any thoughts
about matching, I have no clue how tolerant this little transmitter is.
Hmm, maybe put a 3db attenuator on the transmitter output, into the
LPF, then another 3db attenuator between the LPF and the antenna.
Then my transmitter's happy, and my filter is happy.


You might find it useful to look at what the LPFM people are doing for
antennas:
https://www.google.com/search?q=lpfm+antenna&tbm=isch
Remember, the stranger it looks, the better it works.

Ummm... what problem are you trying to solve?

Who said I have a problem? ;-)

I'll add, I have messed with the Ramsey FM transmitter and a couple of
others, This transmitter works great, and they're down to about $60 now,
half what I paid two years ago. The newer models go up to 7 watts,
if you can believe the specs.
I run my internet radio into the FM transmitter so I can listen to it
around the home.

Mikek



If you're in the United States, you are subject to FCC Part 15 rules.
These rules are based (amongst other things) on Effective Radiated Power
(ERP). So if you install an antenna with gain, you have to cut your
power.

And IIRC, the transmitter must also be certified as a Part 15 device,
which it doesn't look like yours is - at least there is no indication of
that. If you get caught (and it seems the FCC has been clamping down on
unlicensed stations), you will be in for a hefty fine.

Unless you have a very large yard, you should be able to cover it with a
certified transmitter


--
==================
Remove the "x" from my email address
Jerry, AI0K

==================

On Sun, 01 Dec 2013 09:49:32 -0600, amdx wrote:

Think again please.
I did, a couple times.

Keep trying. Enlightenment requires suffering. Ask any philosopher.

I wondered, how does the ground (the dirt) under the radial ground
affect the pattern?

Actually, almost anything conductive or absorptive affects the antenna
pattern. In the case of "ground", I'm not talking about earth ground.
Rather, all the metal and conductive components the comprise your
house.

Then I thought: The classic pattern is not exact, otherwise I'd get no
signal in my house with the antenna on the roof.

Correct. Theory is idealized reality. To see reality, drugs like LSD
are sometimes helpful. When searching for enlightenment in antenna
design, I prefer prescription pain killers, to dull the suffering.

Also (I thinked) just changing from the 8" rubber ducky to the the 1/4
wave on the roof will make a huge difference.

That depends on what's inside the 8" rubber ducky antenna. 1
wavelength at 100 Mhz is about 118" making 8" = 0.07 wavelengths long.
That's right at the borderline where the antenna pattern falls apart
and gain starts to drop. Of course, that assumes that the rubber
ducky is properly matched to 75 ohms or is a helical antenna. What
happens with short monopole antennas (not rubber ducky antennas) is
that as the antenna shrinks, the gain remains roughly the same as a
1/4 wave monopole. With matching, the bandwidth becomes narrow. (You
can have gain, bandwidth or size... pick any two). I think rubber
ducky (end fed helical) antennas are roughly the same. However, at
0.1 wavelengths, the gain finally starts to drop. I did a crude study
of the effect on monopoles:
http://www.LearnByDestroying.com/jeffl/antennas/Monopole/index.html
The numbers in the file names are the antenna length. For example,
monopole_0_0250 is 1/4 wave long. The NEC files are suppose to be in
the NEC directory, but seems to have evaporated. I'll fix later.

Will I knew I could! We have an upside down building not far from here.
The better question, is there a good reason to mount the antenna upside
down?

Yes, if you are on top of a mountain, and are stuck with antenna that
is end fed and suffers from pattern uptilt. Using a realistic model
of both the structure and the antenna, it can be demonstrated that
most of the RF is going to heating the sky and talking to birds. In
other words, little RF is going to the ground, where the mobiles and
handhelds are hiding. By inverting the antenna, usually on a tower
outrigger, the RF is redirected BELOW the horizon and more towards the
ground. Such problems are very common at higher frequencies (above
400 MHz) where vertical radiation patterns are narrow, and gains are
high.
http://www.proxim.com/products/knowledge-center/calculations/calculations-downtilt-coverage-radius
However, you're probably not on top of a mountain and do not have
enough gain for vertical radiation angle to be a problem at 100 MHz.

Darn, not an original idea!

I've never had an original idea in my life. Everything I say or do is
based on the work of others (shoulders of giants and such). The trick
to an original idea is getting away with stealing the idea, and making
it sound original. See the broken US patent system for how that
works.

If I did turn it upside down, what would the feedline do to the pattern?
The feed line will mangle the pattern.
So why did I ask, I knew that.

Second opinion perhaps? The question really boils down to how does a
tower or pipe affect the antenna pattern since it's the mounting
structure that has a bigger effect than the coax. Of course, that
assume that the antenna has a balun to prevent the coax from
radiating, which can produce all kinds of disgusting changes to the
pattern.

Hmm, vertical dipole,
But, then I'd miss the excitement of paralleling 90* of two 75 ohm
coax cables and the measurements to match 37 ohms to 50 ohms. I wanted
to see that happen. I guess I could still do the experiment.

Not much happens. The mismatch loss between 37 and 50 ohms is about
0.1dB. You can be rather sloppy with coax cables and antenna
impedances and still have a system that sorta works. I use 50 and 75
ohm coax cables almost interchangeably with problems. The problems
appear if the transmitter is unable to transmit into a mismatch and
protests by either shutting down, lowering the TX power, or going into
oscillation. all these are possible and should be tested before using
a mismatched antenna. A mismatch will also have some effect to the
antenna pattern. Where a perfect match is required are for situations
where the reflected power is capable of doing some damage (high TX
power), where you need every bit of RX sensitivity you can squeeze out
of the system (satellite work), or you simply want the very best
system. I don't think your FM BCB setup qualifies for any of these.

Ok, as you might have guessed, a lot of this is, as a previous boss of
mine, used to call "mental masturbation"

http://en.wikipedia.org/wiki/Thought_experiment
The trouble with antennas is that you can't see the RF. We use test
equipment as a blind man uses a cane. At best, you can only get a
rough impression of what is happening. There are always surprises.
Besides, it's amazing how much better things work if you think or
model before you build.

I do intend to mount an antenna outside (again), now, I'm not sure
what type.
The problem I'm solving is, in some areas of my yard, the radio signal
gets buzzy, sometimes turning the radio will fix it, often I have to
move the radio 5ft to get a clear signal.
My transmitter is a CZH-05B, the power is switchable between 0.1 watt
and 0.5 watts. I run it at 0.1 watt in an effort to keep myself out of
trouble. Hmm, as I'm writing I noted I have two 3.0db attenuators before
the antenna, as more keep myself out of trouble units.

I think if you simply calculate the path loss of this system, you're
going to be hurting for sufficient signal. I'm too lazy to do it
right now. Based on previous pirate radio experiences, you'll be
lucky if you get 100 ft range to a portable radio. Try a range test
with the antenna near the ground, and just walking away until the
signal gets noisy.

(Btw, I just modified a 13 element filter to put between the
transmitter and the antenna. Someday I hope to have the equipment to
analyze it and see how well it works ( how well I did). I started with a
TFD6102A and wound new coils and added capacitance as needed. I have not
installed it yet.) I recently bought an HP 141T/8553, if I find a 8555
at a reasonable price, I'll buy it.

Heh-heh. Make me rich and a broken 8555 can be yours. I have 3 of
them but only 1 works, so this will be a repair job. I can probably
fix it, but don't have the time or incentive.
http://www.LearnByDestroying.com/jeffl/pics/home/slides/test-equip-mess.html
You'll find that the hp8554B plugin (0-1200MHz) is more useful for FM
BCB use.

A 13 element filter is going to be lossy. How lossy depends on the
design and construction. I suggest you make some measurements or just
remove the filter and see what happens.

The receive area is small, 120" x 115", the antenna will be mounted
13" in from the long dimension and 16" in from the smaller dimension,
basically in the corner of the lot, mounted 16 ft high.

With a 90 degree vertical radiation pattern, height doesn't really
matter. Just get it closer to the receiver and you should be ok.

Jeff, at this point, I have convinced myself putting a gain antenna on
the roof will solve any problem I may have.

Are you sure? Putting it on the roof will move the receiver about
15ft further away from the antenna and add some minor coax cable
losses. That might be useful if you want to illuminate the
neighborhood, but if you're already having signal strength problems,
it's just going to make it worse. Also, do you have any idea of how
large a "gain antenna" will be at 100 MHz? You might be better of
with a dummy load and leaky coax snaked through the yard.

If not I can still remove
6db of attenuation. So unless you want some mental exercise, don't over
do it!

Mental or metal exercise? I get to help move a 2 ton mill into a
friends garage today. The exercise will not be mental. I'm suppose
to be the "safety" officer, which is a little like hiring the fox to
guard the hen house. If you don't hear from me, you can guess what
happened.

For your amusement. I'll turn it into a web page eventually:
http://www.learnbydestroying.com/jeffl/antennas/dish-move-project/
Moving and aligning big 600 lb dish antennas is easy. Polar mount
alignments are easy. Equatorial mounts are difficult. I had a little
too much fun with the cutting torch.

I think you suggested a vertical dipole with downtilt. Any thoughts
about matching, I have no clue how tolerant this little transmitter is.

Build a folded dipole out of twinlead and strips of dry pine or
plastic. Plenty of instructions on the web. Add a 300 ohm to 75 ohm
balun to match the RG-6/u. Mount it horizontally or vertically, it
doesn't matter. Position it as close to your working area as
possible. Do whatever is necessary to keep it away from conductive or
absorptive objects, such as walls, trees, towers, poles, people, and
junk. Optimizing a wide beamwidth pattern is a waste of effort.

Don't read these:
http://www.pcs-electronics.com/guide_antenna.php
http://www.radiobrandy.com/FMAntenna.html
http://www.part15.us
http://www.radiobrandy.com
They might give you some more ideas and produce more mental
masturbation.

Hmm, maybe put a 3db attenuator on the transmitter output, into the
LPF, then another 3db attenuator between the LPF and the antenna.
Then my transmitter's happy, and my filter is happy.

Have you measured your power output? A 100 MHz scope across a 50 ohm
load will suffice. (Remember that it's -3dB down at 100MHz). Measure
the peak to peak voltage. Divided by 2.8 to get RMS voltage. Square
that and divide by your dummy load resistance to get power.

Ummm... what problem are you trying to solve?
Who said I have a problem? ;-)

If people did not have problems to solve, nothing would ever happen.
If you need a problem, just ask, and I'll supply one for you.

I'll add, I have messed with the Ramsey FM transmitter and a couple of
others, This transmitter works great, and they're down to about $60 now,
half what I paid two years ago. The newer models go up to 7 watts,
if you can believe the specs.

Define "works great". You wouldn't be asking such questions if it
works as expected.

I run my internet radio into the FM transmitter so I can listen to it
around the home.

I just turn up the volume control to get the same effect.
--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

Before too much theorizing takes place, why not try just placing it in a
convenient location in the house -- you might be pleasantly surprised.
If that doesn't work, then, and only then, it becomes a technical
problem.

Irv VE6BP

"amdx" wrote in message
...
I have a low power FM transmitter that I use for in my house and yard.
I want to put a 1/4 wave vertical on the roof of my home. The 1/4 wave
vertical will be made as many have seen from a UHF panel mount connector
with the vertical on the center pin and the four radials soldered to the
holes for the screws.
Like this,
https://encrypted-tbn1.gstatic.com/i...M00RrltFyCH-LA
Only bigger :-)

Looking at the pattern of a 1/4 wave vertical, I think I could best
cover my yard with the pattern upside down.

Can I mount the antenna upside down?

Is this feasible?

If I did turn it upside down, what would the feedline do to the pattern?

Is there a better physical layout to avoid pattern distortion caused by
the feedline?

Mikek

On 12/1/2013 11:29 AM, Jeff Liebermann wrote:
On Sun, 01 Dec 2013 09:49:32 -0600, amdx wrote:

Think again please.
I did, a couple times.

Keep trying. Enlightenment requires suffering. Ask any philosopher.

I'm only a little masochistic, I'll suffer some but unless it's
something I really want I'm easily distracted.

I wondered, how does the ground (the dirt) under the radial ground
affect the pattern?

Actually, almost anything conductive or absorptive affects the antenna
pattern. In the case of "ground", I'm not talking about earth ground.
Rather, all the metal and conductive components the comprise your
house.

Then I thought: The classic pattern is not exact, otherwise I'd get no
signal in my house with the antenna on the roof.

Correct. Theory is idealized reality. To see reality, drugs like LSD
are sometimes helpful. When searching for enlightenment in antenna
design, I prefer prescription pain killers, to dull the suffering.

Ya, I have those for problems between S1/L5 and L5/L4, some days I can
get a lot done other days, I'd rather watch TV.


Also (I thinked) just changing from the 8" rubber ducky to the the 1/4
wave on the roof will make a huge difference.

That depends on what's inside the 8" rubber ducky antenna. 1
wavelength at 100 Mhz is about 118" making 8" = 0.07 wavelengths long.
That's right at the borderline where the antenna pattern falls apart
and gain starts to drop. Of course, that assumes that the rubber
ducky is properly matched to 75 ohms or is a helical antenna. What
happens with short monopole antennas (not rubber ducky antennas) is
that as the antenna shrinks, the gain remains roughly the same as a
1/4 wave monopole. With matching, the bandwidth becomes narrow. (You
can have gain, bandwidth or size... pick any two). I think rubber
ducky (end fed helical) antennas are roughly the same. However, at
0.1 wavelengths, the gain finally starts to drop. I did a crude study
of the effect on monopoles:
http://www.LearnByDestroying.com/jeffl/antennas/Monopole/index.html
The numbers in the file names are the antenna length. For example,
monopole_0_0250 is 1/4 wave long. The NEC files are suppose to be in
the NEC directory, but seems to have evaporated. I'll fix later.

Will I knew I could! We have an upside down building not far from here.
The better question, is there a good reason to mount the antenna upside
down?

Yes, if you are on top of a mountain, and are stuck with antenna that
is end fed and suffers from pattern uptilt. Using a realistic model
of both the structure and the antenna, it can be demonstrated that
most of the RF is going to heating the sky and talking to birds. In
other words, little RF is going to the ground, where the mobiles and
handhelds are hiding. By inverting the antenna, usually on a tower
outrigger, the RF is redirected BELOW the horizon and more towards the
ground. Such problems are very common at higher frequencies (above
400 MHz) where vertical radiation patterns are narrow, and gains are
high.
http://www.proxim.com/products/knowledge-center/calculations/calculations-downtilt-coverage-radius
However, you're probably not on top of a mountain and do not have
enough gain for vertical radiation angle to be a problem at 100 MHz.

Darn, not an original idea!

I've never had an original idea in my life. Everything I say or do is
based on the work of others (shoulders of giants and such). The trick
to an original idea is getting away with stealing the idea, and making
it sound original. See the broken US patent system for how that
works.


I might have back in the 70s I thought about using a modulated laser
to do the wood burning pictures. Might have been there early enough.
Just talked with a laser engraver yesterday, prompted my mind.
btw, could you make PCBs with a laser?

If I did turn it upside down, what would the feedline do to the pattern?
The feed line will mangle the pattern.
So why did I ask, I knew that.

Second opinion perhaps? The question really boils down to how does a
tower or pipe affect the antenna pattern since it's the mounting
structure that has a bigger effect than the coax. Of course, that
assume that the antenna has a balun to prevent the coax from
radiating, which can produce all kinds of disgusting changes to the
pattern.

Hmm, vertical dipole,
But, then I'd miss the excitement of paralleling 90* of two 75 ohm
coax cables and the measurements to match 37 ohms to 50 ohms. I wanted
to see that happen. I guess I could still do the experiment.

Not much happens. The mismatch loss between 37 and 50 ohms is about
0.1dB. You can be rather sloppy with coax cables and antenna
impedances and still have a system that sorta works. I use 50 and 75
ohm coax cables almost interchangeably with problems. The problems
appear if the transmitter is unable to transmit into a mismatch and
protests by either shutting down, lowering the TX power, or going into
oscillation. all these are possible and should be tested before using
a mismatched antenna. A mismatch will also have some effect to the
antenna pattern. Where a perfect match is required are for situations
where the reflected power is capable of doing some damage (high TX
power), where you need every bit of RX sensitivity you can squeeze out
of the system (satellite work), or you simply want the very best
system. I don't think your FM BCB setup qualifies for any of these.

Ok, as you might have guessed, a lot of this is, as a previous boss of
mine, used to call "mental masturbation"

http://en.wikipedia.org/wiki/Thought_experiment
The trouble with antennas is that you can't see the RF. We use test
equipment as a blind man uses a cane. At best, you can only get a
rough impression of what is happening. There are always surprises.
Besides, it's amazing how much better things work if you think or
model before you build.

I do intend to mount an antenna outside (again), now, I'm not sure
what type.
The problem I'm solving is, in some areas of my yard, the radio signal
gets buzzy, sometimes turning the radio will fix it, often I have to
move the radio 5ft to get a clear signal.
My transmitter is a CZH-05B, the power is switchable between 0.1 watt
and 0.5 watts. I run it at 0.1 watt in an effort to keep myself out of
trouble. Hmm, as I'm writing I noted I have two 3.0db attenuators before
the antenna, as more keep myself out of trouble units.

I think if you simply calculate the path loss of this system, you're
going to be hurting for sufficient signal. I'm too lazy to do it
right now. Based on previous pirate radio experiences, you'll be
lucky if you get 100 ft range to a portable radio. Try a range test
with the antenna near the ground, and just walking away until the
signal gets noisy.


Ok, one data set! I have the transmitter then a 3db att. then my LPF
then another 3 db att. and the rubber ducky. I walked 250ft before noise
showed up, then I went back and ran the antenna straight out of the
transmitter.
As you might think things did not work out as expected. I did not get
as far with just the antenna. About 10 or 15ft less.
So, I cruised the yard looking for poor reception, I found two spots,
but move slightly and it's better.

(Btw, I just modified a 13 element filter to put between the
transmitter and the antenna. Someday I hope to have the equipment to
analyze it and see how well it works ( how well I did). I started with a
TFD6102A and wound new coils and added capacitance as needed. I have not
installed it yet.) I recently bought an HP 141T/8553, if I find a 8555
at a reasonable price, I'll buy it.

Heh-heh. Make me rich and a broken 8555 can be yours. I have 3 of
them but only 1 works, so this will be a repair job. I can probably
fix it, but don't have the time or incentive.
http://www.LearnByDestroying.com/jeffl/pics/home/slides/test-equip-mess.html
You'll find that the hp8554B plugin (0-1200MHz) is more useful for FM
BCB use.

I'd need to have a working unit, I'd have major problems with a
repair. Can't I do with the 8555 anything I can do with the 8554?

A 13 element filter is going to be lossy. How lossy depends on the
design and construction. I suggest you make some measurements or just
remove the filter and see what happens.

It didn't show it's self as causing signal degradation. (1 data set)
That's why I want the 8555!

The receive area is small, 120" x 115", the antenna will be mounted
13" in from the long dimension and 16" in from the smaller dimension,
basically in the corner of the lot, mounted 16 ft high.

With a 90 degree vertical radiation pattern, height doesn't really
matter. Just get it closer to the receiver and you should be ok.

Jeff, at this point, I have convinced myself putting a gain antenna on
the roof will solve any problem I may have.

Are you sure?

No.

Putting it on the roof will move the receiver about
15ft further away from the antenna and add some minor coax cable
losses. That might be useful if you want to illuminate the
neighborhood, but if you're already having signal strength problems,
it's just going to make it worse. Also, do you have any idea of how
large a "gain antenna" will be at 100 MHz? You might be better of
with a dummy load and leaky coax snaked through the yard.

If not I can still remove
6db of attenuation. So unless you want some mental exercise, don't over
do it!

Mental or metal exercise? I get to help move a 2 ton mill into a
friends garage today. The exercise will not be mental. I'm suppose
to be the "safety" officer, which is a little like hiring the fox to
guard the hen house. If you don't hear from me, you can guess what
happened.

For your amusement. I'll turn it into a web page eventually:
http://www.learnbydestroying.com/jeffl/antennas/dish-move-project/
Moving and aligning big 600 lb dish antennas is easy. Polar mount
alignments are easy. Equatorial mounts are difficult. I had a little
too much fun with the cutting torch.

I think you suggested a vertical dipole with downtilt. Any thoughts
about matching, I have no clue how tolerant this little transmitter is.

Build a folded dipole out of twinlead and strips of dry pine or
plastic. Plenty of instructions on the web. Add a 300 ohm to 75 ohm
balun to match the RG-6/u. Mount it horizontally or vertically, it
doesn't matter. Position it as close to your working area as
possible. Do whatever is necessary to keep it away from conductive or
absorptive objects, such as walls, trees, towers, poles, people, and
junk. Optimizing a wide beamwidth pattern is a waste of effort.

Don't read these:
http://www.pcs-electronics.com/guide_antenna.php
http://www.radiobrandy.com/FMAntenna.html
http://www.part15.us
http://www.radiobrandy.com
They might give you some more ideas and produce more mental
masturbation.

Hmm, maybe put a 3db attenuator on the transmitter output, into the
LPF, then another 3db attenuator between the LPF and the antenna.
Then my transmitter's happy, and my filter is happy.

Have you measured your power output? A 100 MHz scope across a 50 ohm
load will suffice. (Remember that it's -3dB down at 100MHz). Measure
the peak to peak voltage. Divided by 2.8 to get RMS voltage. Square
that and divide by your dummy load resistance to get power.


I feel like you getting even for the MFJ1800 :-)

I have a 300Mhz scope, just to complicate things. Measured 7.5Vpp.
Sooo, I get 0.143 watts, so much for spec's.

If I install the rubber ducky in place of the 50 ohm, I get 8.3Vpp.

Later, I'll connect my MFJ259 to the rubber ducky, and see what it says.


Ummm... what problem are you trying to solve?
Who said I have a problem? ;-)

If people did not have problems to solve, nothing would ever happen.
If you need a problem, just ask, and I'll supply one for you.

I'll add, I have messed with the Ramsey FM transmitter and a couple of
others, This transmitter works great, and they're down to about $60 now,
half what I paid two years ago. The newer models go up to 7 watts,
if you can believe the specs.

Define "works great". You wouldn't be asking such questions if it
works as expected.

Ya, maybe, but I'm running low power through 6db of attenuation with
two walls and an aluminum screened porch between my problem area and the
transmitter. Problem area is near my work shed and other side of the
metal bar greenhouse. Minor problems, like I say I can move the radio
5ft and solve the problem.


I run my internet radio into the FM transmitter so I can listen to it
around the home.

I just turn up the volume control to get the same effect.

The neighbors would think I'm weird, I listen to Science 360,
Gunsmoke, Phil Hendrie, what a train wreck!

Need to go take over for my wife at the business, I'll reread what you
said here and look at links when I get to work, it's a tough job
(well, not really) but somebodies got to do it.
Thanks, Mikek

On 12/1/2013 11:48 AM, Irv Finkleman wrote:
Before too much theorizing takes place, why not try just placing it in a
convenient location in the house -- you might be pleasantly surprised.
If that doesn't work, then, and only then, it becomes a technical
problem.

Irv VE6BP


That's good advice, except I have three different audio inputs that all
land where I now have the transmitter.
Besides, we like technical problems! :-)

After my last response to Jeff when I measured the output voltage, I
just realized I can check the loss through the LPF. Hot dog! Can't
wait to get home.
Mikek

El 01-12-13 16:49, amdx escribió:
On 11/30/2013 10:30 PM, Jeff Liebermann wrote:
On Sat, 30 Nov 2013 21:42:38 -0600, amdx wrote:

I have a low power FM transmitter that I use for in my house and yard.
I want to put a 1/4 wave vertical on the roof of my home. The 1/4 wave
vertical will be made as many have seen from a UHF panel mount
connector
with the vertical on the center pin and the four radials soldered
to the
holes for the screws.
Like this,
https://encrypted-tbn1.gstatic.com/i...M00RrltFyCH-LA

Only bigger :-)

Unless you use stiff elements, they will sag. At 100MHz, 1/4
wavelength is about 75 cm (2.5 ft) long.

Looking at the pattern of a 1/4 wave vertical, I think I could best
cover my yard with the pattern upside down.

Think again please.

I did, a couple times.
I wondered, how does the ground (the dirt) under the radial ground
affect the pattern?
Then I thought: The classic pattern is not exact, otherwise I'd get no
signal in my house with the antenna on the roof.
Also (I thinked) just changing from the 8" rubber ducky to the the 1/4
wave on the roof will make a huge difference.

Can I mount the antenna upside down?

Yes.
Will I knew I could! We have an upside down building not far from here.
The better question, is there a good reason to mount the antenna
upside down?

Is this feasible?

Yes. It's commonly done with UHF antennas on mountain top sites.

Darn, not an original idea!


If I did turn it upside down, what would the feedline do to the
pattern?

The feed line will mangle the pattern.

So why did I ask, I knew that.


Is there a better physical layout to avoid pattern distortion caused
by the feedline?

Yes. Use a vertical dipole on a tower or a coaxial antenna on a vent
pipe.

Hmm, vertical dipole,
But, then I'd miss the excitement of paralleling 90* of two 75 ohm
coax cables and the measurements to match 37 ohms to 50 ohms. I wanted
to see that happen. I guess I could still do the experiment.

The alleged problem with a ground plane antenna is that there is a
slight vertical uptilt of the beam. It varies with the height above
the rooftop ground, but my guess(tm) is maybe 5 to 10 degrees uptilt.
I just ran a simple ground plane simulation using 4NEC2 and found that
the uptilt is small when the vertical beamwidth of the ground plane is
about 90 degrees. In other words, inverting the antenna isn't going
to do much good at delivering the signal towards the ground. You're
better off with an antenna that puts the main lobes where your
receiver is located or perhaps has some gain and/or downtilt. Without
a description of your house and yard, I can't offer any suggestions.
Numbers please?

Ok, as you might have guessed, a lot of this is, as a previous boss of
mine, used to call "mental masturbation"
I do intend to mount an antenna outside (again), now, I'm not sure
what type.
The problem I'm solving is, in some areas of my yard, the radio signal
gets buzzy, sometimes turning the radio will fix it, often I have to
move the radio 5ft to get a clear signal.
My transmitter is a CZH-05B, the power is switchable between 0.1 watt
and 0.5 watts. I run it at 0.1 watt in an effort to keep myself out of
trouble. Hmm, as I'm writing I noted I have two 3.0db attenuators
before the antenna, as more keep myself out of trouble units.
(Btw, I just modified a 13 element filter to put between the
transmitter and the antenna. Someday I hope to have the equipment to
analyze it and see how well it works ( how well I did). I started with
a TFD6102A and wound new coils and added capacitance as needed. I have
not installed it yet.) I recently bought an HP 141T/8553, if I find a
8555 at a reasonable price, I'll buy it.
The receive area is small, 120" x 115", the antenna will be mounted
13" in from the long dimension and 16" in from the smaller dimension,
basically in the corner of the lot, mounted 16 ft high.

You mentioned 0.1 W with 2, 3 dB attenuators, so you may have around
10..20mW at the antenna (depending on cable loss). This should be more
then enough to cover your yard if you find some clear frequency.

I would just try the quarter wave antenna with three or 4 radials on
the roof (not up side down). Due to scattering on the roof, and may be
some common mode current on the feed line, you will have sufficient
signal indoors. If you live in shielded room or heavy bunker/shelter,
you may not have indoor coverage.

You may give us some height and lot size info.



Jeff, at this point, I have convinced myself putting a gain antenna on
the roof will solve any problem I may have. If not I can still remove
6db of attenuation. So unless you want some mental exercise, don't
over do it!
I think you suggested a vertical dipole with downtilt. Any thoughts
about matching, I have no clue how tolerant this little transmitter is.
Hmm, maybe put a 3db attenuator on the transmitter output, into the
LPF, then another 3db attenuator between the LPF and the antenna.
Then my transmitter's happy, and my filter is happy.


You might find it useful to look at what the LPFM people are doing for
antennas:
https://www.google.com/search?q=lpfm+antenna&tbm=isch
Remember, the stranger it looks, the better it works.

Ummm... what problem are you trying to solve?

Who said I have a problem? ;-)

I'll add, I have messed with the Ramsey FM transmitter and a couple of
others, This transmitter works great, and they're down to about $60
now, half what I paid two years ago. The newer models go up to 7 watts,
if you can believe the specs.
I run my internet radio into the FM transmitter so I can listen to it
around the home.

Mikek



Best regards,

--
Wim
PA3DJS
www.tetech.nl
Please remove abc first in case of PM

On Sun, 01 Dec 2013 13:05:23 -0600, amdx wrote:

I'm only a little masochistic, I'll suffer some but unless it's
something I really want I'm easily distracted.

For me, it's the math that causes the most suffering. I have 3
calculators, one PC, and a Mac on my desk, and I still can't get the
right answer. Maybe I should buy an iPad?

It is impossible to achieve enlightenment without suffering. In other
words, things become more obvious after you screw everything up,
destroy some equipment, and injure yourself. It becomes very plain
how something works after it tries to kill you. You can do it slowly,
rapidly, or periodically, they all work. In some cultures,
flagellation has been shown to be effective. The only problem is that
this all applies to the models of antennas, not the actual
performance. That's pure magic.

I might have back in the 70s I thought about using a modulated laser
to do the wood burning pictures. Might have been there early enough.
Just talked with a laser engraver yesterday, prompted my mind.
btw, could you make PCBs with a laser?

Sure. No copper required. Just burn some tracks into the FR4/G10
with the laser. They should be sufficiently conductive to work with
low power circuits using solder paste of connections. However, to be
sure, you might want to measure the ohms/square of carbonized PCB
material. However, you're behind the times. The hot ticket are
printed PCB's using an inkjet printer and nanoparticle inks. I wrote
a rant on the topic in a mailing list last week. Unfortunately, the
archive is for members only.

Light reading:
http://dl.acm.org/citation.cfm?id=2493486
http://www.techweekeurope.co.uk/news/silver-ink-solution-for-cheaper-faster-flexible-circuits-54967

Years ago, I thought I had a better idea of PCB construction. I would
roll a rounded point over the unplated G10/FR14 PCB forming groves for
traces. I would then fill the grooves with conductive solder paste
using ordinary silk screen techniques. When I tried it, it actually
worked. However, the process was slow because anything faster than
maybe 1/2" per second would burn the PCB from the friction.

Ok, one data set! I have the transmitter then a 3db att. then my LPF
then another 3 db att. and the rubber ducky. I walked 250ft before noise
showed up, then I went back and ran the antenna straight out of the
transmitter.
As you might think things did not work out as expected. I did not get
as far with just the antenna. About 10 or 15ft less.

Ummm... a good question would be why that's happening. Plenty of
possibilities including that your yard is an RF black hole. However,
my guess(tm) is that nothing is very well matched to 50/75 ohms and
the coax, attenuator, and LPF are radiating (leaking). You should
probably fix that although 250 ft is more than I would have expected
with a commodity receiver.

Heh-heh. Make me rich and a broken 8555 can be yours. I have 3 of
them but only 1 works, so this will be a repair job. I can probably
fix it, but don't have the time or incentive.
http://www.LearnByDestroying.com/jeffl/pics/home/slides/test-equip-mess.html
You'll find that the hp8554B plugin (0-1200MHz) is more useful for FM
BCB use.

I'd need to have a working unit, I'd have major problems with a
repair. Can't I do with the 8555 anything I can do with the 8554?

I charge extra if it works. The 8554 goes to 1.2Ghz. The hp8555a
goes to from 10 MHz to 18GHz. With an external mixer to 43GHz.
They're quite different plug-ins. You'll need an external hp8445b
preselector to get rid of spurs and strong interfering signals.

I'll dig out the plugs tonite and see what I find. Maybe I'll get
lucky and one will fix itself.

Incidentally, the mixer likes to blow up in the hp8555a when you
transmit into it. The fix:
http://www.k3pgp.org/hp8555a.htm

I feel like you getting even for the MFJ1800 :-)

I've thought about that. Please inspect any packages you receive from
me with a bomb sniffer before opening.

I have a 300Mhz scope, just to complicate things. Measured 7.5Vpp.
Sooo, I get 0.143 watts, so much for spec's.

I was going to suggest you try a 75 ohm load, but it looks like the
xmitter is specified at 50 ohms.
http://www.elecsky.com
http://www.czhfm.com/datasheet/CZH-05B-Manual.pdf
Looks like the rubber ducky is tuned to the FM band.
http://www.elecsky.com/index.php?main_page=product_info&cPath=10&products _id=5

If I install the rubber ducky in place of the 50 ohm, I get 8.3Vpp.

If you run it open load, you'll probably see even more voltage. The
power measurement is only valid with a proper 50 ohm dummy load or 50
ohm antenna.

Later, I'll connect my MFJ259 to the rubber ducky, and see what it says.

The display will probably say "give up and get a real antenna".

Ya, maybe, but I'm running low power through 6db of attenuation with
two walls and an aluminum screened porch between my problem area and the
transmitter.

Now you tell me. Perhaps all the junk in the way might have an effect
on the signal level? Instead of a new antenna, perhaps moving the
transmitter or running a longer coax run might be useful?

Minor problems, like I say I can move the radio
5ft and solve the problem.

Too easy. Moving the radio or antenna does not demonstrate how they
work. Without suffering there can be no enlightenment.

I just turn up the volume control to get the same effect.

The neighbors would think I'm weird, I listen to Science 360,
Gunsmoke, Phil Hendrie, what a train wreck!

Yeah, you have a problem. Perhaps if you play what the neighbors
prefer to hear, they might be more tolerant of your bizarre listening
habits. My usual mix is 60's electric acid rock, New Age, and
classical music. I haven't determined if this is the result of brain
damage, or the cause.

Need to go take over for my wife at the business, I'll reread what you
said here and look at links when I get to work, it's a tough job
(well, not really) but somebodies got to do it.

Bah Humbug (T'is the season to be grumpy).


--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558