On 5/25/2011 5:17 PM, John KD5YI wrote:
On 5/25/2011 3:51 PM, Jim Lux wrote:
On 5/24/2011 5:17 PM, John KD5YI wrote:
On 5/24/2011 6:11 PM, Jim Lux wrote:
On 5/24/2011 2:54 PM, Dave Platt wrote:


I'm using 75' of
professionally assembled RG8X which is required to get from the
radio to
the antenna.

That's probably costing you about half of your power (assuming a
typical RG8X-type coax). Some lower-loss types (e.g. LMR-240 are
better than this.


The results are all over the map. A piece of Cable TV cable might
not be
a bad choice, if you can scrounge one. The 75 ohms probably isn't a big
deal.

At 144 MHz, bigger in diameter almost always beats fancier dielectric
(that is, the .405 inch RG-8, RG-213 flavors will usually beat any of
the quarter inch cables (RG-6, RG-8X, LMR240, etc.) because dielectric
losses aren't a big driver.. it's the IR loss in the center conductor.
RG-11, for instance, has less than 1.2dB loss for a matched 75 foot
line, and for the 1.5:1 mismatch, the loss only goes up 0.1 dB. (RG-11
type coax has a solid dielectric, and is pretty darn rugged stuff)

75 feet, at 144 MHz
LMR240 - 2.2 dB
Belden 8215 (RG-6A) - 2.5 dB
Belden 9258 (RG-8x) - 3.0 dB
Tandy RG-8x - 3.1 dB
Belden 8267 (RG-213) - 1.9 dB
Wireman CQ110 (RG-213) - 1.6 dB
Belden 8237 (RG-8) - 1.7 dB
belden 8213 (RG-11) = 1.2dB


Huh? 75 ft of RG-11 has almost 8dB of loss at 146MHz. 75 ft of LMR240
has 9.7dB of loss at 146 MHz.

I won't go through your entire list.

Check out http://www.vk1od.net/calc/tl/tllc.php


That's what I used..
Sure you got feet and not meters?

B9219, 75ft, 146 MHz = 1.811dB

Yes, Jim, Ralph pointed that out to me yesterday and I posted an apology
to him. I see that I should also analogize to you for my mistake.
^^^^^^^^^
Thanks to you both. Apologize

John

On 5/25/2011 3:17 PM, John KD5YI wrote:
On 5/25/2011 3:51 PM, Jim Lux wrote:

Yes, Jim, Ralph pointed that out to me yesterday and I posted an apology
to him. I see that I should also analogize to you for my mistake.



Darn newsreader that didn't have all the messages loaded.. I saw Ralph's
comment and your reply. Such is life..

Now, if you want some high loss coax.. can I interest you in some tiny
coax made of stainless steel? It's for cryogenic applications so it has
very, very low thermal conductivity, but it also has really high loss. I
don't think you want to be running kilowatts (or even watts) through it.

On 5/25/2011 7:37 PM, Jim Lux wrote:
On 5/25/2011 3:17 PM, John KD5YI wrote:
On 5/25/2011 3:51 PM, Jim Lux wrote:

Yes, Jim, Ralph pointed that out to me yesterday and I posted an apology
to him. I see that I should also analogize to you for my mistake.



Darn newsreader that didn't have all the messages loaded.. I saw Ralph's
comment and your reply. Such is life..

Now, if you want some high loss coax.. can I interest you in some tiny
coax made of stainless steel? It's for cryogenic applications so it has
very, very low thermal conductivity, but it also has really high loss. I
don't think you want to be running kilowatts (or even watts) through it.

Well, thanks, Jim, for your kind offer. However I have plenty of lossy
cable now. I only use in the lab because other options are difficult to
handle.

Cheers,
John

On 5/24/2011 8:08 PM, Ralph Mowery wrote:
"John wrote in message
...

75 feet, at 144 MHz
LMR240 - 2.2 dB
Belden 8215 (RG-6A) - 2.5 dB
Belden 9258 (RG-8x) - 3.0 dB
Tandy RG-8x - 3.1 dB
Belden 8267 (RG-213) - 1.9 dB
Wireman CQ110 (RG-213) - 1.6 dB
Belden 8237 (RG-8) - 1.7 dB
belden 8213 (RG-11) = 1.2dB


Huh? 75 ft of RG-11 has almost 8dB of loss at 146MHz. 75 ft of LMR240 has
9.7dB of loss at 146 MHz.

I won't go through your entire list.

Check out http://www.vk1od.net/calc/tl/tllc.php

Cheers,
John


John you need to see where you went wrong. The numbers Jim listed are
either correct or very close. I did not bother to do the calculations, but
looking at a 100 foot chart, the numbers are very close and no where near
the numbers you have.

I thought you may have looked at the web page and missed it defauls to
meters, but that does not seem to be the case to me.



According to the loss calculator at Times Microwave the loss at 144 MHz
for a 75 length of LMR 240 is 2.952. 100 METERS is 9.687.

Perhaps you misread.

tom
K0TAR

On 5/25/2011 8:44 PM, tom wrote:
On 5/24/2011 8:08 PM, Ralph Mowery wrote:
"John wrote in message
...

75 feet, at 144 MHz
LMR240 - 2.2 dB
Belden 8215 (RG-6A) - 2.5 dB
Belden 9258 (RG-8x) - 3.0 dB
Tandy RG-8x - 3.1 dB
Belden 8267 (RG-213) - 1.9 dB
Wireman CQ110 (RG-213) - 1.6 dB
Belden 8237 (RG-8) - 1.7 dB
belden 8213 (RG-11) = 1.2dB


Huh? 75 ft of RG-11 has almost 8dB of loss at 146MHz. 75 ft of LMR240
has
9.7dB of loss at 146 MHz.

I won't go through your entire list.

Check out http://www.vk1od.net/calc/tl/tllc.php

Cheers,
John


John you need to see where you went wrong. The numbers Jim listed are
either correct or very close. I did not bother to do the calculations,
but
looking at a 100 foot chart, the numbers are very close and no where near
the numbers you have.

I thought you may have looked at the web page and missed it defauls to
meters, but that does not seem to be the case to me.



According to the loss calculator at Times Microwave the loss at 144 MHz
for a 75 length of LMR 240 is 2.952. 100 METERS is 9.687.

Perhaps you misread.

tom
K0TAR


Oops, needed to do this one level up. Should have responded to John.

tom
K0TAR

On May 24, 2:43*pm, (Dave Platt) wrote:


a *very* deep multipath
cancellation effect playing out... maybe interference between a
edge-diffraction path involving the office building, and reflections
from nearby trees. *


Not a Sea Story and relevant to my learning an important multipath
lesson:

In 1974, I was on an aircraft carrier at a pier in Long Beach
Shipyard. Ship's TV sigs not so good, so I ran a cable from the CPO
lounge TV out and up to a flight deck catwalk. On the catwalk, I
mounted a small all-channel antenna on a mast strapped to the rail.
The transmitters (Mt. Wilson) were located away from that side. All
very good pictures. In about two months, when the ship moved into
drydock, it was turned 180, so I rotated our TV antenna to
compensate. No good. Signals arriving across the flight deck were
all awful. Unwatchable.

I suspected reflections from the flight deck, so I moved the antenna
all the way aft, where it was receiving through clear air again.
Bingo! Even through the added 150' of cable I needed, we got our nice
pictures back.

"Sal"

On May 22, 2:04*pm, 'Captain' Kirk DeHaan
wrote:
I'm living in a wooded area and am trying to hit our club repeater
reliably. *It's cloudy now so I'm and getting a bit of ducting but I
have a lot of trees, mostly poplars, in the direct path. *I would have a
line of sight if not for the trees as I'm up enough in altitude. *I can
cut the trees, they're mine, but finding the right ones is difficult and
i don't want to waste the whole grove.

I go from keying the repeater with no intelligible signal to not being
able to hit it. *Today I actually have an S meter reading due to the
clouds. I am currently using a J-pole and will put up a Yagi soon but
wonder if NVIS would work on 2m? *I have only seen references to it
being applied in HF.

'Captain' Kirk DeHaan
N6SXR

Im convinced that my J antenna that I used while camping radiated
mostly verticaly. The situation sounds very similar to yours. I
couldnt hit the repeater back home with 50 watts using the J- while
my wife could make contacts on her HT on the same repeater, Her
antenna was either a telescoping .5 wl or 5/8 wl connected directly to
her HT.

Jimmie

Hello Kirk,

I sent you a PM with a result from Radio Mobile.

It took a long time to get RMW working, and getting the terrain data
into the SW.

It is 10 years ago that I used RMW and that computer I don’t have
anymore. I had to start from scratch. First checked with Dutch terrain
data to see whether the results are meaningful.

When you look to the path profile, you have a huge margin (received
power -76 dBm). I used 10W into a 2 dBi antenna (on both sides). I
attached the path profile as generated by RMW (Personal Mail only).

Even reducing your antenna height to 1m AGL gives sufficient margin
(Prx -86 dBm). I used 30m AGL for the repeater antenna. You have 1
degree elevation towards the repeater, that is huge (we don't have
that in the Netherlands).

Assuming the data is correct, it is really strange that you can't hit
the repeater. I couldn’t find were to set vegetation and cities, but
even this shouldn't be a problem. I hope some other people can confirm
the results from RMW.

With kind regards,


Wim
PA3DJS
www.tetech.nl

On 5/24/2011 11:05 PM, 'Captain' Kirk DeHaan wrote:
Dave Platt said the following on 5/24/2011 2:54 PM:
In ,
'Captain' Kirk wrote:

All of this leads me to think that something else is wrong. I can hit a
repeater 20 miles from me with 5 Watts and its antenna is on a 300 ft
tower. My antenna (half wave end-fed dipole) is on a 20 ft mast.

There may well be something wrong with the antenna. I don't have an SWR
meter handy but will try and borrow one from a club member. The J-pole
was beat around quite a bit over the years but since the radio has a
limiting circuit if the SWR is too far out of whack I am assuming it is
fairly close. It will transmit of full power.

One of the things to know about the American Legion J-pole (and most
vaguely-similar J-poles) is that it has no feedline or mount-point
isolation to speak of. The outside of the feedline coax, and any pipe
or tower or other metal to which you strap the antenna, become part of
the antenna's ground system, and can radiate a significant amount of
RF. This can interact with the RF coming from the main radiator, and
significantly alter the antenna's pattern... it no longer behaves like
an idealized half-wave vertical radiator.

In most installations this doesn't seem to matter all that much... but
it's possible that you've got some sort of weird interaction (feedline
emissions, reflections from the ground or nearby metal, etc.) which is
creating a null in the antenna's pattern in just the wrong direction.
If this is an issue (not all that likely but perhaps possible) you
could insulate the antenna from the mounting mask, and install a choke
(e.g. a few ferrite cores) on the feedline just below the antenna.

It is mounted on an angle bracket about 12" from a mast 20' above my
metal roof. The mast is isolated from roof but is not yet grounded.


Also, the American Legion J-poles are subject to a couple of forms of
mechanical/electrical failure after a few years. The plastic
insulator which spaces apart the radiator and matching arm can degrade
(UV from sunlight is the main offendor, I believe) and crack, allowing
the two arms to change spacing. More subtly, the connection between
the two arms and the metal base can degrade... it's aluminum-to-
aluminum using a set-screw, and the connection can loosen and corrode.

My spacer basically disintegrated. I replaced it with 1/2" pvc pipe. I
measured the spacing at the base and got it as close as possible.

I will check out the other connections. There is obvious aluminum oxide
on the assembly so it is very possible it is down between the parts.

I'll get up on my steep metal roof after the rains stop. :-)


It might be worth checking the spacer (replace if necessary), and
checking and tuning up the set-screw connections (squirt with Liquid
Wrench if necessary, loosen and remove, take out the rods, clean the
ends of the rods and the mounting holes in the place, dab with NoAlOx
or a similar corrosion-blocker, reassemble and tighten).

I'm using 75' of
professionally assembled RG8X which is required to get from the radio to
the antenna.

That's probably costing you about half of your power (assuming a
typical RG8X-type coax). Some lower-loss types (e.g. LMR-240 are
better than this.


Thanks for the suggestions.


Hey, Kirk -

After reading Wim's response, I am more convinced than ever that you
have a problem with your antenna, coax, or transceiver.

What type of coax are you using? Could it have gotten water inside? Are
you using the coax that you used 10 years ago?

Try to think of other question similar to these and we'll get to the
bottom of this.

Cheers,
John

John KD5YI said the following on 5/26/2011 8:56 PM:
On 5/24/2011 11:05 PM, 'Captain' Kirk DeHaan wrote:
Dave Platt said the following on 5/24/2011 2:54 PM:
In ,
'Captain' Kirk wrote:

All of this leads me to think that something else is wrong. I can
hit a
repeater 20 miles from me with 5 Watts and its antenna is on a 300 ft
tower. My antenna (half wave end-fed dipole) is on a 20 ft mast.

There may well be something wrong with the antenna. I don't have an SWR
meter handy but will try and borrow one from a club member. The J-pole
was beat around quite a bit over the years but since the radio has a
limiting circuit if the SWR is too far out of whack I am assuming it is
fairly close. It will transmit of full power.

One of the things to know about the American Legion J-pole (and most
vaguely-similar J-poles) is that it has no feedline or mount-point
isolation to speak of. The outside of the feedline coax, and any pipe
or tower or other metal to which you strap the antenna, become part of
the antenna's ground system, and can radiate a significant amount of
RF. This can interact with the RF coming from the main radiator, and
significantly alter the antenna's pattern... it no longer behaves like
an idealized half-wave vertical radiator.

In most installations this doesn't seem to matter all that much... but
it's possible that you've got some sort of weird interaction (feedline
emissions, reflections from the ground or nearby metal, etc.) which is
creating a null in the antenna's pattern in just the wrong direction.
If this is an issue (not all that likely but perhaps possible) you
could insulate the antenna from the mounting mask, and install a choke
(e.g. a few ferrite cores) on the feedline just below the antenna.

It is mounted on an angle bracket about 12" from a mast 20' above my
metal roof. The mast is isolated from roof but is not yet grounded.


Also, the American Legion J-poles are subject to a couple of forms of
mechanical/electrical failure after a few years. The plastic
insulator which spaces apart the radiator and matching arm can degrade
(UV from sunlight is the main offendor, I believe) and crack, allowing
the two arms to change spacing. More subtly, the connection between
the two arms and the metal base can degrade... it's aluminum-to-
aluminum using a set-screw, and the connection can loosen and corrode.

My spacer basically disintegrated. I replaced it with 1/2" pvc pipe. I
measured the spacing at the base and got it as close as possible.

I will check out the other connections. There is obvious aluminum oxide
on the assembly so it is very possible it is down between the parts.

I'll get up on my steep metal roof after the rains stop. :-)


It might be worth checking the spacer (replace if necessary), and
checking and tuning up the set-screw connections (squirt with Liquid
Wrench if necessary, loosen and remove, take out the rods, clean the
ends of the rods and the mounting holes in the place, dab with NoAlOx
or a similar corrosion-blocker, reassemble and tighten).

I'm using 75' of
professionally assembled RG8X which is required to get from the
radio to
the antenna.

That's probably costing you about half of your power (assuming a
typical RG8X-type coax). Some lower-loss types (e.g. LMR-240 are
better than this.


Thanks for the suggestions.


Hey, Kirk -

After reading Wim's response, I am more convinced than ever that you
have a problem with your antenna, coax, or transceiver.

What type of coax are you using? Could it have gotten water inside? Are
you using the coax that you used 10 years ago?

Try to think of other question similar to these and we'll get to the
bottom of this.

Cheers,
John

John,

I believe it is either the trees or the antenna. The coax is new and
the transceiver worked fine last time I used it. Also works fine with
this setup getting into the repeater on Schweitzer , 145.230, with 5
watts and the signal report from a gentleman I spoke to was 59. That is
a clear shot and a few miles closer. Although the profiles show there
should be a clear shot to the .780 repeater I can gurantee there is a
wall of trees on the first little ridge on the profile. I found that my
club, which I've only been with for a month, has an SWR meter and an
antenna analyzer. I hope to borrow them to see what's up. In the
meantime I will pull the J-pole down and clean it up as suggested.
There is considerable aluminum oxide on the outside of the parts so
there may be some between the base and uprights. When I put it back up
I will move it 180 degrees from it current location. That will only
move it about 2' but who knows.

--
'Captain' Kirk DeHaan
N6SXR

"Beam me up Scotty, there's no intelligent life here"