Dear Rick, N6RK:

If you believe that none of the "other" analyzers will work at your site
because of the presence of strong signals from below 1700 kHz, then you
could do one of the following:

1. You could build a high-pass filter to go between analyzer and antenna
to attenuate the MF signals. I have heard of people doing this successfully
such that the filter is essentially transparent at HF.

2. You could add one or more band stop resonators that can be tuned to
number 1 and really cut down the one or two most strong broadcast signals.

3. You could search for a used or new bridge type of instrument. They
tend to be insensitive to off-frequency signals.

4. Many types of antennas will deliver little of a signal that is far
away in frequency. An inverted L is expected to deliver a lot of signal
from nearby MF stations. A balanced LPDA with a shorting strap at its far
end is expected to pick up little from vertically polarized MF stations.

Let the group know what type of antennas you wish to analyze.

73 Mac N8TT

--
J. Mc Laughlin; Michigan U.S.A.
Home:
"Rick Karlquist N6RK" wrote in message
news:cS4Cd.611717$wV.601406@attbi_s54...
The N2PK would be the best, except that it only runs when
connected to a laptop. I don't have a laptop, and if I did, I
wouldn't want to carry it out to the antennas, and furthermore,
laptop displays are usually not visible outdoors during daylight.
All the others don't work if you have nearby AM BCB stations
like I do.

Still looking for an antenna analyzer I can really use.

Rick N6RK

"Rick Karlquist N6RK" wrote in message
news:cS4Cd.611717$wV.601406@attbi_s54...
The N2PK would be the best, except that it only runs when
connected to a laptop. I don't have a laptop, and if I did, I
wouldn't want to carry it out to the antennas, and furthermore,
laptop displays are usually not visible outdoors during daylight.
All the others don't work if you have nearby AM BCB stations
like I do.

Still looking for an antenna analyzer I can really use.

Rick N6RK

Rick, you don't HAVE to use a laptop, or carry it to the antenna or worry
about being able to see the LCD. Simply take your N2PK, couple it to the
feedline in the shack, (and your desktop computer) do the OSL calibration
out at the antenna end of the feedline and measure the antenna from the
comfort of your operating position. You've just calibrated out the feedline.
You can REALLY use the VNA.

Regards

W4ZCB

"J. Mc Laughlin" wrote in message
...
Dear Rick, N6RK:

If you believe that none of the "other" analyzers will work at your
site
because of the presence of strong signals from below 1700 kHz, then you
could do one of the following:

1. You could build a high-pass filter to go between analyzer and
antenna
to attenuate the MF signals. I have heard of people doing this
successfully
such that the filter is essentially transparent at HF.

The filter needs to have no group delay in the band of measurement (not
just flat group delay and amplitude). It is impossible to build a high
pass filter with no group delay.



2. You could add one or more band stop resonators that can be tuned to
number 1 and really cut down the one or two most strong broadcast signals.

Too much trouble.



3. You could search for a used or new bridge type of instrument. They
tend to be insensitive to off-frequency signals.

I have a GR-916 bridge if I really must make a measurement.



4. Many types of antennas will deliver little of a signal that is far
away in frequency. An inverted L is expected to deliver a lot of signal
from nearby MF stations. A balanced LPDA with a shorting strap at its far
end is expected to pick up little from vertically polarized MF stations.

Let the group know what type of antennas you wish to analyze.

I have a 90 foot vertical for 160 meters. I use it because it gets
out very well. Unfortunately, it is also a good BCB receive
antenna, developing nearly a volt of RF.

Rick N6RK



73 Mac N8TT

--
J. Mc Laughlin; Michigan U.S.A.
Home:
"Rick Karlquist N6RK" wrote in message
news:cS4Cd.611717$wV.601406@attbi_s54...
The N2PK would be the best, except that it only runs when
connected to a laptop. I don't have a laptop, and if I did, I
wouldn't want to carry it out to the antennas, and furthermore,
laptop displays are usually not visible outdoors during daylight.
All the others don't work if you have nearby AM BCB stations
like I do.

Still looking for an antenna analyzer I can really use.

Rick N6RK

Rick Karlquist N6RK wrote:

1. You could build a high-pass filter to go between analyzer and
antenna
to attenuate the MF signals. I have heard of people doing this
successfully
such that the filter is essentially transparent at HF.

The filter needs to have no group delay in the band of measurement (not
just flat group delay and amplitude). It is impossible to build a high
pass filter with no group delay.

[...]

I have a 90 foot vertical for 160 meters. I use it because it gets out
very well. Unfortunately, it is also a good BCB receive antenna,
developing nearly a volt of RF.

Any impedance/network analyser is going to need a BCB-reject filter in
order to handle that level of interference. However, imperfections in
the filter don't matter with a more advanced VNA such as the N2PK
design, because the filter can be included *inside* the calibration
loop.

As Harold W4ZCB says, a long coax can be included inside the calibration
loop as well, so you could make the measurements from home... in
principle. But you'd have to do a lot of shuttling back and forth
between the shack and the antenna to swap connectors, start the VNA etc.
At Rick's QTH (www.n6rk.com) that would involve a *lot* of travelling
time.

Seriously, Rick, if the lack of a laptop is all that's stopping you...
then get a laptop already! (Almost any old wreck will run an N2PK VNA.)
Add an awning, a camping table, chair and cooler, and you're all set for
accurate impedance measurements in the field.

I'm going to be doing a lot of that in the next two years, but the
environmental problems will be slightly different. Where can I find a
laptop with a screen demister and two-speed wipers?



--
73 from Ian G3SEK 'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.co.uk/g3sek

Any impedance/network analyser is going to need a BCB-reject filter in
order to handle that level of interference. However, imperfections in
the filter don't matter with a more advanced VNA such as the N2PK
design, because the filter can be included *inside* the calibration
loop.

GM Ian, Actually, I have used the N2PK under the same conditions that Rick
has and you DON'T need the reject filter. That volt is an aggregate number
and at any 2-3 Hz bandwidth that the VNA detector is looking at, it's at the
uVolt level and not a bother. (Unless you tune TO the BC signal itself of
course!) As for the walk, would probably do most of us some good, but I even
substituted the guy that wanted the measurements made and a pair of $5. FRS
radios for the walk. Works fine if you really want to measure the antenna.
Rick can put the feedline, his transformers and the kitchen sink inside the
cal loop and still measure his antenna if he REALLY wanted to use it.

Used Laptops with a parallel port (And worn out battery) are running 25-50
bucks around here. Had one given to me that Alice plays the cardgame with
using the charger. Most will still hold a charge for an hour or so.

I'm going to be doing a lot of that in the next two years, but the
environmental problems will be slightly different. Where can I find a
laptop with a screen demister and two-speed wipers?

Try a portable igloo, Rain-X doesn't work very well.

Regards
W4ZCB

Dear Rick:
OK. Your vertical antenna certainly picks up a lot of stray RF.

However, one of the beauties of using a network analyzer is the ability
to characterize the transmission line (even 1000 feet of it) and a filter
that is between the network analyzer and the antenna, AND THEN to have the
effects of all of the stuff between the analyzer and antenna removed so as
to leave the properties of the antenna.

One has to measure the "stuff" (transmission line +) with the "stuff"
disconnected from the antenna. Even if you went out to the antenna, you
would need (temporarily) to disconnect the "stuff" from the antenna.


This scheme really works. One has some front-end-load required in order
to characterize the "stuff," but then it is straight forward.

73 Mac N8TT

--
J. Mc Laughlin; Michigan U.S.A.
Home:

I had a laptop a long time ago, and I couldn't
read the screen outdoors. Are the newer ones
better?

Rick N6RK

"Ian White, G3SEK" wrote in message
...
Rick Karlquist N6RK wrote:

Add an awning, a camping table, chair and cooler, and you're all set for
accurate impedance measurements in the field.

--
73 from Ian G3SEK 'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.co.uk/g3sek

Rick Karlquist N6RK wrote:
I had a laptop a long time ago, and I couldn't
read the screen outdoors. Are the newer ones
better?

If the LCD that you remember was an old passive matrix type, you may be
pleasantly surprised by a modern active matrix (TFT) display.

LCDs are still not as bright as a CRT, though, so I was more than
half-serious in suggesting an awning for shade.

--
73 from Ian G3SEK 'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.co.uk/g3sek

But I want to adjust the matching network at the base
of the antenna. I need real time feedback to when I
turn a know. An indicator 1000 ft away is useless.

Rick N6RK

"J. Mc Laughlin" wrote in message
...
Dear Rick:
OK. Your vertical antenna certainly picks up a lot of stray RF.

However, one of the beauties of using a network analyzer is the
ability
to characterize the transmission line (even 1000 feet of it) and a filter
that is between the network analyzer and the antenna, AND THEN to have the
effects of all of the stuff between the analyzer and antenna removed so as
to leave the properties of the antenna.

One has to measure the "stuff" (transmission line +) with the "stuff"
disconnected from the antenna. Even if you went out to the antenna, you
would need (temporarily) to disconnect the "stuff" from the antenna.


This scheme really works. One has some front-end-load required in
order
to characterize the "stuff," but then it is straight forward.

73 Mac N8TT

--
J. Mc Laughlin; Michigan U.S.A.
Home:

Rick Karlquist N6RK wrote:
My old laptop was an active matrix, and it still wasn't
readable in sunlight, or even in a room on a sunny day
near a window.

I have the same problem with my IC-756PRO.
--
73, Cecil http://www.qsl.net/w5dxp


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