[Elecraft] Antenna Analyzer (FA-VA4)

[Jim Brown]

On 12/1/2017 10:30 AM, Wes Stewart wrote:
> What calibrations are you doing that take an hour?
>
> You can do a master cal with lots of points in 5 minutes.

Yes.  AND, more important, calibrations can be saved for standard 
measurement setups, so when you're always using a previous setup, 
there's no need to recalibrate -- you simply load the previous calibration.

> I use mine in the field all the time using a Win 10 touch screen 
> tablet.  The software is phenomenal.  I've been doing network analysis 
> since the days when the calibration curve was a grease pencil line on 
> a CRT.  I (my employer) bought one of the first HP8510s sold to a 
> non-governmental agency.  It cost IIRC north of $200K, was in a 4-foot 
> rack cabinet and probably weighed 500 pounds.  With an admittedly 
> reduced frequency range, the VNWA3 is for all practical purposes the 
> equal of the '8510 and I can hold it in the palm of my hand!

Like Wes, I've been doing swept complex (magnitude and phase) 
measurements since 1982, first in the audio range, later at RF.  I 
bought the VNWA3e about 4 years ago, and have found it to be the 
excellent that Wes describes.  It has an excellent TDR function. Another 
important advantage of this unit over others is that it is self-powered 
from the USB port, so no external power is required.

TDR can be VERY useful when troubleshooting an antenna or feedline 
problem, and the higher the analyzer can sweep, the more fine detail it 
can show. The VNWA can sweep to 1.3 GHz.  Few analyzers the do TDR can 
sweep nearly this high. A wideband TDR sweep can find all the splices 
and many defects in a feedline.

Another use of TDR is that it allows us to measure an antenna at the 
shack end of a feedline, find the electrical length of the feedline with 
the TDR feature, and then using Smith Chart software (free), subtract 
out the feedline to see the Z and SWR at the feedpoint.

Note also that this is a vector NETWORK analyzer. A NETWORK analyzer has 
input and output ports, so that in addition to impedance and TDR, it can 
also measure the response of any system. You can, for example, measure 
the effectiveness of filters, and the coupling between adjacent 
antennas. These plots of bandpass filter response were done with the 
VNWA 3e. Note that you can display several views of the same 
measurement. These display SWR, attenuation, and reflection loss, and 
the markers show values within the passband and on other ham bands.

http://audiosystemsgroup.com/BandpassFilterData.htm

These data were used to generate this report that ran in National 
Contest Journal in 2014.

http://k9yc.com/BandpassFilterSurvey.pdf

> With a good external frequency standard (I use a Bodnar GPSDO) it 
> makes an excellent frequency counter and works as a limited function 
> spectrum analyzer.

Yes, and quite versatile in that mode. Inexpensive SDRs also provide 
limited spectrum analyzer functions, and some of them are quite good IF 
the user is careful to prevent overload and knows how to avoid false 
responses from aliasing.

> One other thing.  On my 160-meter inverted-L antenna I receive a 
> couple of AM broadcast stations at -3dBm.  If I limit the lower sweep 
> frequency to 1.7 MHz the VNWA3 is unaffected.  I suspect some of these 
> other boxes are not so resilient. 

This can be very important -- many analyzers get blown away by AM 
broadcast stations.

Here are links to the mfr, SDRKits. The VNWA is NOT a kit, it is built 
and fully tested. You want the model 3E or 3EC with calibration kit and 
cables.

https://www.sdr-kits.net/index.php?route=web/pages&page_id=29_29

https://www.sdr-kits.net/index.php?route=web/pages&page_id=68_68

73, Jim K9YC