RadioBanter - Antenna analyzers, opinions please...

On Tue, 24 Aug 2010 11:25:08 -0400, "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!

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]

Actually, my MFJ catalog page for their antenna analyzers shows an
accessory, the mfj-731 "tunable analyzer filter." It's made for
operating an antenna analyzer in "presence of strong rf fields."

Personally, I have no experience with the filter -- my mfj-269 seems
to work okay, even with a 50-kw KTSA about a mile and a half away on
550 khz.

bob
k5qwg

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