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