On 23.08.2010 21:15, Peter O. Brackett wrote:
Antenna Newsgroup Denizens:

Apart from the professional 'lab grade' (and undoubtedly very expensive)
devices made by the likes of Agilent, there are on the amateur market
several antenna analyzers that are more reasonably priced.

I'm currently considering the purchase of such a device, and so...

I'm interested in hearing opinions, pro-con arguments, and/or receiving
pointers to reviews of such devices.

All thoughts and comments will be appreciated, unbiased or not.

Thanks!

-- Pete k1po
-- Indialantic By-the-Sea, FL

Hi, there are quite many choices between tiny hand-held units like Autek
Research VA-1 vector analyzer and computer/laptop connected VNAs like
N2PK VNA which gives more accurate measurements. This last one is
basically a kit, but not too complicated to build at home and is quite
multi-use device.
Both have been useful and done their jobs well.

Kari B

Roy:

[snip]
"Roy Lewallen" wrote in message
...
..
..
..
The bottom line is that I don't trust a single value or its comparison to
36 or 40 ohms as being a reliable indication of efficiency. You either
need to look for convergence of the feedpoint resistance as Peter
proposed, or even better yet, look for convergence of field strength
values at a fixed location as you increase the number of radials.

Roy Lewallen, W7EL
[snip]

That's exactly what I thought.

Since; (a) I don't know my soil characteristics and (b) because of property
limitations that dictate a non-uniform radial field, I felt that all I can
do is to lay down radials in the property area I have avaliable until I see
the change in Zin due to adding more radials become insignificant, then...
I'm done!

I don't really care what the exact value of Zin = Rin + jXin ends up to be,
since there is nothing I can do about it anyway. When I reach the point in
laying down radials to where I can't reduce Zin much by adding more radials,
I will then have the most efficient radial field with the lowest ground
resistance Rg that I can get for my money and effort [smile].

Heh, heh... Money is only money, the effort, hmmm... well that's me crawling
on my hands and knees for hours digging in the dirt (sand) in the blazing
hot Florida sunshine, heat and humidity!

When I arrive at that point in burying radials, I believe that I can then
tune out any reactive part of Zin with my 'tuner' and and end up feeding
power into the remaining resistance Rin which then should be the sum of the
vertical element radiation resistance Rr and whatever value I have ended up
with for ground resistance Rg.

I just won't know what the value of Rr and Rg is, but I will know that I
have achieved the most efficient radial field I could put down here at my
place.

Is this right?

-- Pete k1po
-- Indialantic By-the-Sea, FL

PS: I took your advice and did some reading on simple impedance bridges,
and I saw one that you had designed in one of my ARRL pubs. Cool!

Another idea I came upon that allow the use of those antenna analyzers in a
situation where they can be somewhat immune to BC interference involved a
two step process that went as follows...

(1) Hook up a transmitter through an antenna tuner to the antenna and ground
systems under test and tune the tuner for zero reflected power with a 50 Ohm
reflectometer (VSWR meter). Then (2) disconnect the tuner from the antenna,
and without disturbing the tuner settings, hook a 50 Ohm load to the input
side where the transmitter was connected, and then use the antenna analyzer
to measure the impedance looking back into the output, or antenna terminals,
of the tuner. This impedance should be the conjugate of Zin. Here the
analyzer may not be as affected by potentially strong BC RF signals picked
up by the lengthy antenna element.

Thanks Walt!

"walt" wrote in message
...
On Aug 23, 8:38 pm, Gary wrote:
On Aug 23, 4:53 pm, "Peter O. Brackett"
wrote:



Roy:

Thanks for your input on the effects of interference from other
transmitters, especially BC transmitters, point well taken.

I suppose one might add some kind of carefully designed passive
filtering to
the devices to 'notch' out offending BC stations, etc...

But... that would be messy and complicated.

Using a bridge with a tuned detector seems a much better approach. I do
have an old MFJ Rx resistance bridge at hand, but I was looking for a
little
bit better accuracy. I must check e-bay, etc... for prices for a used
bridge of the GR class you have.

My current problem could likly be solved by using one of my (so-called)
VSWR
meters, but I felt I might like to get a little more metrological
capability
for a few bucks.

I've never had a vertical antenna before and currently I'm laying out a
radial field under a new vertical antenna. I just wanted to know when to
stop laying down radials.

I figure that I just need to measure the input impedance of the antenna
Zin
at my frequencies of interest and record the (hopefully decreasing)
impedance values as I lay down more radials. My assumption is that Zin =
Zant + Rg. where Zant includes the reactance and radiation resistance of
the radiator element at my frequency of interest and Rg is the ground
resistance. Hopefully Rg should decrease as I add raials. I intend to
quit
adding radials when the impedance decrease becomes 'negligible' ( In the
sense of received S units [smile]).

Thanks again!

-- Pete k1po
-- Indialantic By-the-Sea, FL

"Roy Lewallen" wrote in message

...

I have only one comment which applies to most if not all of the amateur
level products, as well as a very high quality HP impedance meter I
used
years ago.

I live about 15 miles from hilltops where the local AM, FM, and TV
broadcast towers are. The signals from those stations are strong
enough to
overwhelm the broad bandwidth detection circuitry in the analyzers
(and HP
vector impedance meter) I've used, resulting in meaningless readings
when
connected to an antenna. I find that I grab my MFJ antenna analyzer
for a
host of jobs like measuring a ferrite core impedance, checking the
length
of a piece of coax, and so forth. But for me it's just about useless
for
the job of analyzing actual antennas. When I need to measure antenna
impedance I dust off an old GR bridge and use a portable receiver for
the
detector in order to reject the strong ambient signals.

Of course this isn't a problem for everyone, but it sure is for me and
I
don't think my situation is unusual for an urban environment. I've had
to
put common mode chokes on my thermometer thermocouple wire, my light
meter
connecting wire, scope leads, and even in audio circuitry to keep the
RF
out. But even one strong local station might be enough to upset a
typical
antenna analyzer.

Roy Lewallen, W7EL

On 8/23/2010 11:15 AM, Peter O. Brackett wrote:
Antenna Newsgroup Denizens:

Apart from the professional 'lab grade' (and undoubtedly very
expensive)
devices made by the likes of Agilent, there are on the amateur market
several antenna analyzers that are more reasonably priced.

I'm currently considering the purchase of such a device, and so...

I'm interested in hearing opinions, pro-con arguments, and/or
receiving
pointers to reviews of such devices.

All thoughts and comments will be appreciated, unbiased or not.

Thanks!

-- Pete k1po
-- Indialantic By-the-Sea, FL- Hide quoted text -

- Show quoted text -

Hi Pete, If you are evaluating a radial field for a vertical, then
the value you should be shooting for is 30-35 ohms, with no
reactance. As you know this is 1/2 the impedance of a 1/2 wave
dipole-70 ohms in free space. I have never done this, but an
impedance below 40 ohms with little reactance should provide you with
an efficient vertical. Once you get around this value, I guess there
is nothing to be gained by adding more radials. What your analyzer
tells you, as others have mentioned, depends on the rf in the area.

Gary N4AST

Hi Pete, long time since I've seen a post from you on this NG!

Pete, I'd take Roy's route and use a GR impedance bridge. I've used
the GR-1606A and the 1606B for the last 50 years. If you're not
familiar with it it's been the standard impedance-measuring device for
AM BC antennas for more than 50 years. It's accuracy cannot be beaten.
These bridges were expensive when new, but they are available rather
inexpensively now, and are stable as a rock. And as Roy said, they use
either a millivolt meter or a tunable receiver as the detector. Using
the receiver, interfering signals picked up with the antenna being
measured are eliminated, thus not degrading the accuracy of the
impedance measurement.

The GR-1606A measures from below 500 kHz up to 60 MHz. The GR-1602
measures well into the VHF range. If you should try one I know you'll
like it.

Walt, W2DU

PS--If you'd like to see the results of measuring W2DU's antenna
impedances, I refer you to Reflections, Chapter 15, Tables 15-4, 15-5,
and Fig 15-1, which is a graph of the data in the Tables. If you don't
have a copy of Reflections you can see this data on my web page at
www.w2du.com. Just select 'Read Chapters from Reflections 2'.

Danny:

Hey thanks! I read your reference. Nice piece of work!

I guess I didn 't realize just how big those BC RF signals on the antenna
element would actually be.
And for that matter, how little front end selectivity the analog inputs of
those amateur antenna analyzers contain. None!

Hmmm... the amateur antenna analyzer sales literature I read don't mention
this problem at all. The ads all 'brag' on the 'super features' of the
devices. [smile]

I presume there must be more than a few dissappointed antenna analyzer
purchasers who find this fact out the hard way.

Thanks again for the great reference.

-- Pete k1po
-- Indialantic By-the-Sea, FL


"Danny" wrote in message ...
I've been pretty satisfied with the AIM 4170. Check this out.

http://arraysolutions.com/images/Tun...m_Vertical.pdf

73,
Danny, K6MHE

On Mon, 23 Aug 2010 17:53:33 -0400, Peter O. Brackett wrote:

Roy:

Thanks for your input on the effects of interference from other
transmitters, especially BC transmitters, point well taken.

I suppose one might add some kind of carefully designed passive
filtering to the devices to 'notch' out offending BC stations, etc...

But... that would be messy and complicated.

Using a bridge with a tuned detector seems a much better approach. I do
have an old MFJ Rx resistance bridge at hand, but I was looking for a
little bit better accuracy. I must check e-bay, etc... for prices for a
used bridge of the GR class you have.

My current problem could likly be solved by using one of my (so-called)
VSWR meters, but I felt I might like to get a little more metrological
capability for a few bucks.

I've never had a vertical antenna before and currently I'm laying out a
radial field under a new vertical antenna. I just wanted to know when
to stop laying down radials.

I figure that I just need to measure the input impedance of the antenna
Zin at my frequencies of interest and record the (hopefully decreasing)
impedance values as I lay down more radials. My assumption is that Zin
= Zant + Rg. where Zant includes the reactance and radiation resistance
of the radiator element at my frequency of interest and Rg is the ground
resistance. Hopefully Rg should decrease as I add raials. I intend to
quit adding radials when the impedance decrease becomes 'negligible' (
In the sense of received S units [smile]).

Thanks again!

-- Pete k1po
-- Indialantic By-the-Sea, FL


"Roy Lewallen" wrote in message
...
I have only one comment which applies to most if not all of the amateur
level products, as well as a very high quality HP impedance meter I used
years ago.

I live about 15 miles from hilltops where the local AM, FM, and TV
broadcast towers are. The signals from those stations are strong enough
to overwhelm the broad bandwidth detection circuitry in the analyzers
(and HP vector impedance meter) I've used, resulting in meaningless
readings when connected to an antenna. I find that I grab my MFJ
antenna analyzer for a host of jobs like measuring a ferrite core
impedance, checking the length of a piece of coax, and so forth. But
for me it's just about useless for the job of analyzing actual
antennas. When I need to measure antenna impedance I dust off an old GR
bridge and use a portable receiver for the detector in order to reject
the strong ambient signals.

Of course this isn't a problem for everyone, but it sure is for me and
I don't think my situation is unusual for an urban environment. I've
had to put common mode chokes on my thermometer thermocouple wire, my
light meter connecting wire, scope leads, and even in audio circuitry
to keep the RF out. But even one strong local station might be enough
to upset a typical antenna analyzer.

Roy Lewallen, W7EL

On 8/23/2010 11:15 AM, Peter O. Brackett wrote:
Antenna Newsgroup Denizens:

Apart from the professional 'lab grade' (and undoubtedly very
expensive) devices made by the likes of Agilent, there are on the
amateur market several antenna analyzers that are more reasonably
priced.

I'm currently considering the purchase of such a device, and so...

I'm interested in hearing opinions, pro-con arguments, and/or
receiving pointers to reviews of such devices.

All thoughts and comments will be appreciated, unbiased or not.

Thanks!

-- Pete k1po
-- Indialantic By-the-Sea, FL

"Gary" wrote in message
...
On Aug 23, 4:53 pm, "Peter O. Brackett"
wrote:
Roy:

Thanks for your input on the effects of interference from other
transmitters, especially BC transmitters, point well taken.

I suppose one might add some kind of carefully designed passive filtering
to
the devices to 'notch' out offending BC stations, etc...

But... that would be messy and complicated.

Using a bridge with a tuned detector seems a much better approach. I do
have an old MFJ Rx resistance bridge at hand, but I was looking for a
little
bit better accuracy. I must check e-bay, etc... for prices for a used
bridge of the GR class you have.

My current problem could likly be solved by using one of my (so-called)
VSWR
meters, but I felt I might like to get a little more metrological
capability
for a few bucks.

I've never had a vertical antenna before and currently I'm laying out a
radial field under a new vertical antenna. I just wanted to know when to
stop laying down radials.

I figure that I just need to measure the input impedance of the antenna
Zin
at my frequencies of interest and record the (hopefully decreasing)
impedance values as I lay down more radials. My assumption is that Zin =
Zant + Rg. where Zant includes the reactance and radiation resistance of
the radiator element at my frequency of interest and Rg is the ground
resistance. Hopefully Rg should decrease as I add raials. I intend to quit
adding radials when the impedance decrease becomes 'negligible' ( In the
sense of received S units [smile]).

Thanks again!

-- Pete k1po
-- Indialantic By-the-Sea, FL

"Roy Lewallen" wrote in message

...



I have only one comment which applies to most if not all of the amateur
level products, as well as a very high quality HP impedance meter I used
years ago.

I live about 15 miles from hilltops where the local AM, FM, and TV
broadcast towers are. The signals from those stations are strong enough
to
overwhelm the broad bandwidth detection circuitry in the analyzers (and
HP
vector impedance meter) I've used, resulting in meaningless readings
when
connected to an antenna. I find that I grab my MFJ antenna analyzer for
a
host of jobs like measuring a ferrite core impedance, checking the
length
of a piece of coax, and so forth. But for me it's just about useless for
the job of analyzing actual antennas. When I need to measure antenna
impedance I dust off an old GR bridge and use a portable receiver for
the
detector in order to reject the strong ambient signals.

Of course this isn't a problem for everyone, but it sure is for me and I
don't think my situation is unusual for an urban environment. I've had
to
put common mode chokes on my thermometer thermocouple wire, my light
meter
connecting wire, scope leads, and even in audio circuitry to keep the RF
out. But even one strong local station might be enough to upset a
typical
antenna analyzer.

Roy Lewallen, W7EL

On 8/23/2010 11:15 AM, Peter O. Brackett wrote:
Antenna Newsgroup Denizens:

Apart from the professional 'lab grade' (and undoubtedly very
expensive)
devices made by the likes of Agilent, there are on the amateur market
several antenna analyzers that are more reasonably priced.

I'm currently considering the purchase of such a device, and so...

I'm interested in hearing opinions, pro-con arguments, and/or receiving
pointers to reviews of such devices.

All thoughts and comments will be appreciated, unbiased or not.

Thanks!

-- Pete k1po
-- Indialantic By-the-Sea, FL- Hide quoted text -

- Show quoted text -

Hi Pete, If you are evaluating a radial field for a vertical, then
the value you should be shooting for is 30-35 ohms, with no
reactance. As you know this is 1/2 the impedance of a 1/2 wave
dipole-70 ohms in free space. I have never done this, but an
impedance below 40 ohms with little reactance should provide you with
an efficient vertical. Once you get around this value, I guess there
is nothing to be gained by adding more radials. What your analyzer
tells you, as others have mentioned, depends on the rf in the area.

Gary N4AST

My experience with the MFJ-269 agrees with Roy's -- fine for bench top
measurements but nearly useless for antenna checks if you're close to
high-powered broadcasters. (I'm even closer than he is!)

I have been thinking of an antenna impedance measurement setup using a
HF bridge of some kind, driven by a high-level generator to swamp out
the ambient junk. My 100 wattHF rig followed by a power attenuator
(say, 10db?) would serve to drive the bridge, I would guess.

Anybody have some thoughts on this approach - pro or con? What kind of
bridge would be good?

Larry Coyle, K1QW

In article ,
"Larry Coyle" wrote:

My experience with the MFJ-269 agrees with Roy's -- fine for bench top
measurements but nearly useless for antenna checks if you're close to
high-powered broadcasters. (I'm even closer than he is!)

I have been thinking of an antenna impedance measurement setup using a
HF bridge of some kind, driven by a high-level generator to swamp out
the ambient junk. My 100 wattHF rig followed by a power attenuator
(say, 10db?) would serve to drive the bridge, I would guess.

Anybody have some thoughts on this approach - pro or con? What kind of
bridge would be good?

Larry Coyle, K1QW

The price you pay for living on a Hilltop.... Good for you and every
other RF source......

--
Bruce in alaska
add path after fast to reply

On Aug 23, 8:09*pm, Roy Lewallen wrote:
On 8/23/2010 5:38 PM, Gary wrote:



Hi Pete, *If you are evaluating a radial field for a vertical, then
the value you should be shooting for is 30-35 ohms, with no
reactance. *As you know this is 1/2 the impedance of a 1/2 wave
dipole-70 ohms in free space. *I have never done this, but an
impedance below 40 ohms with little reactance should provide you with
an efficient vertical. *Once you get around this value, I guess there
is nothing to be gained by adding more radials. *What your analyzer
tells you, as others have mentioned, depends on the rf in the area.

Gary N4AST

The actual value you get when the radial system loss is minimal depends
on a number of factors, including the height and diameter of the
vertical. I've also seen convergence to other resistance values when the
ground was dry on the surface but apparently wet at some depth below. In
that case, radial current can be significant at quite a distance from
the antenna (as opposed to the exponential-looking decay you see in the
current on radials buried in moist ground), making the system act more
like a system of elevated radials. In those systems, radial length also
plays a role in determining the feedpoint resistance value.

The bottom line is that I don't trust a single value or its comparison
to 36 or 40 ohms as being a reliable indication of efficiency. You
either need to look for convergence of the feedpoint resistance as Peter
proposed, or even better yet, look for convergence of field strength
values at a fixed location as you increase the number of radials.

Roy Lewallen, W7EL

Hi Roy, I agree that field strength would be the best indicator of
efficiency as additional radials are laid down. However, for the
average Joe Ham trying to figure out how many radials is enough, and
all he has is an antenna anlyzer, what do you recommend?

Seems to me, with a 1/4 wave vertical of diameter large enough to
minimize I^2*R losses over average ground, if you add enough radials
to get the impedance to 35+/-j0 ohms as measured by the antenna
analyzer, you should be good to go. An additional check with the
analyzer could be the SWR bandwidth. If the swr was 1.7 across a
broad range then the 35 ohms is all ground losses. If the 1.7 swr
bandwidth is very narrow then you have a high Q antenna, and very
efficient at the operating frequency. Does this make sense?

Gary N4AST

Peter O. Brackett wrote:
Danny:

Hey thanks! I read your reference. Nice piece of work!

I guess I didn 't realize just how big those BC RF signals on the
antenna element would actually be.
And for that matter, how little front end selectivity the analog inputs
of those amateur antenna analyzers contain. None!

It's a matter of how much you want to pay. If you want highly selective
over the frequency range we generally use, you have to be prepared to
pay and pay well.


Hmmm... the amateur antenna analyzer sales literature I read don't
mention this problem at all. The ads all 'brag' on the 'super features'
of the devices. [smile]



I presume there must be more than a few dissappointed antenna analyzer
purchasers who find this fact out the hard way.

Could be. As for Amateur use, there are lots of options. There's even a
bare bones MFJ SWR tester that will be fine for 90 percent of what most
of us want to do. Most amateurs just want a low SWR so their rigs don't
fold back on power - for good or bad, that is the case.

- 73 de Mike N3LI -

As others have noted, it really is almost a case of you get what you pay for with antenna analyzers. Lesser models are prone to interference especially around high power installations and will give you only pieces of information you may need. One of my personal favorites is the TE-1000 impedance analyzer made by TOMCO which measures pretty much everything you could hope for and has a high amount of protection from interference. I know several AM and even television broadcast guys that use this around towers without issues.

Larry Coyle wrote:

I have been thinking of an antenna impedance measurement setup using a
HF bridge of some kind, driven by a high-level generator to swamp out
the ambient junk. My 100 wattHF rig followed by a power attenuator
(say, 10db?) would serve to drive the bridge, I would guess.

Anybody have some thoughts on this approach - pro or con? What kind of
bridge would be good?


You've got two basic approaches to dealing with strong interference:
1) Make the signal you're measuring huge, so the interference is small..
any detector works
2) Use a tuned narrow band detector.


I would think you could use a simple resistive bridge with option #1,
although the tricky part is getting phase measurements. The current
crop of PC based VNAs and the like rely on having a handy quadradure
source. You could probably use a TAPR VNA, with a linear amplifier on
the Tx port and pads on the Rx port, after calibrating out the amp/pads.

A narrow band detector would be easier. This is sort of how the "noise
bridge" schemes work.. they use your HF receiver as the narrow band
detector. Again, almost any bridge would work for scalar (non-phase)
measurements.

Another approach is the old "three voltmeter meter" technique, which is
essentially a broadband detector and half a bridge, and lends itself to
high power.

The real challenge isn't in making the measurement, but in automating it
so that you can do a "sweep" conveniently. For spot measurements,
almost anything works well enough, but if you want to make 100
measurements it gets real tedious.