Topband: New MFJ 259C available

[Grant Saviers]

I have made sweeps of my 160m T on many occasions as I tuned it, added 
elevated radials, and then installed a remote series capacitor switch to 
tune the entire band per a W8JI suggestion.  There was no interference 
from AMBC, I'd be glad to forward the sweeps.  My current QTH does not 
have a nearby BC transmitter however.   At my former QTH in San Jose, CA 
I had elevated clear line of sight to a 50kw BC 1Mhz at 3 miles.  The 
MFJ269 was useless (sold) and my AIM4170 (pre VNWA, still use it now and 
then) worked but showed obvious glitches in the sweeps of both 40m and 
80m elevated verticals on metal roofs.  I had 1v of the BC signal on my 
power lines.

I haven't needed RF measurement of resistance better than 1% in any 
antenna, choke, or filter testing.  There is also a 3rd party VI test 
kit (and support in the software) for the VNWA that enables more 
accurate testing of very low and high Z, as the VNWA 50 ohm internal 
bridge is good for about a 20:1 ratio or so.  I have a 6.5 digit 4 lead 
DMM but never thought I needed to measure a standard that accurately.  
The yahoo VNWA group gets into very detailed and esoteric (to me) 
discussions of the psec and fF issues in standards, cables, and 
connectors for GHz work.  There is a raft of good info from basic 
tutorials to esoterica linked from the posts.  Also, HP/Agilent have a 
large number of excellent VNA technical reports/tutorials also available 
on the web.  Tom's (DG8SAQ) manual is comprehensive, he is continuously 
adding software enhancements, and is responsive to posts.

I've tuned/measured several 5B4AGN filter kits and other off the shelf 
single band units, some of them went back for re-tuning as they were out 
of spec.  Measuring ferrite chokes is easy.  I've probably tuned/checked 
a dozen different antennas.  If you calibrate at the far end of the 
feedline, then the measurement is accurate at the antenna at its input 
terminals - cool and no climbing.  I'm still a bit of a novice, am 
learning at lot and working up to retuning a 70cm multicavity filter as 
I have not yet used the time domain filter tuning technique.

Overall, the VNWA is my most frequently used test equipment, a VNA is 
the RF engineers VOM.

Grant KZ1W


On 3/4/2014 7:25 AM, Paul Christensen wrote:
> I had a look at the matching Rosenberger calibration standards and for 
> the money, the kit is a bargain.  At first, I was disappointed to see 
> what amounts to only 1% resistive load accuracy.  The displayed image 
> on the website shows a calibration standard that reads about 49.5 
> ohms.  But, the software automatically compensates for the disparity.  
> It's possible to use a DMM with 4-wire resistance capabilities to 
> measure the exact DC resistance then enter the value in a table to get 
> excellent operating accuracy, certainly better than 0.1%.  Depending 
> on the accuracy needed, the VNWA software allows for several other 
> important compensating factors.
>
> http://www.hamcom.dk/VNWA/Rosenberger%20Cal%20standards_rev2.pdf
>
> My only concern with the VNWA is in its ability to measure Topband 
> antenna systems where sweeps are required into the AMBC band.  I'm 
> still looking for input from anyone who has made such measurements.
>
> Paul, W9AC
> _________________
> Topband Reflector Archives - http://www.contesting.com/_topband
>