Well,
Based on the replys I purchased an HP vector volt meter to measure
antenna impedance. So far so good. Also based on the replys here I
rigged up a simple circuit to 'look' at the antenna from the shack. I
feed the antenna with a constant power supply and placed a small
resistor in series with the center feed of a coax. I then used a dual
trace scope to look at the current (across the resistor) and the voltage
(across the feed line it self after the resistor. Wala! As the frequency
changed the the phase changed. I must be about the 10 millionth person
to rediscover this.
Now to the questions. The antenna is a center loaded vertical tuned for
3970 kc. The points of zero phase difference were about 3000 kc and 6000
kc. There was defiantly a phase shift at 3970 even that is the point of
minimum SWR.
1. How do I use the vector volt meter in place of the above to read
phase? The hookup is an RF generator, a coax feed line, and an antenna.
I would like to measure the antenna and ground charactoristics.
2. Is there a way to determine the antenna and ground charactoristics
ffrom the shack with the vector volt meter?
3. I have not used Smith Charts. I assume they are part of the answer to 2.
Thanks,
Dan
G3rzp@aol.com wrote:
>
>In a message dated 27/02/2005 22:27:11 GMT Standard Time,
>david.kirkby@onetel.net writes:
>
>
>My guess is that the software in
>modern VNAs can take this into account, but I might well be wrong. I'm
>sure there will be an Agilent application note (I mean sales literature)
>on this!!
>
>
>
>It's interesting that even with one of their latest digitally corrected
>doo-dads just back from calibration, you can still get the trace going outside
>
>the periphery of the Smith chart even after calibrating with the short and the
>
>open. Admittedly, that was with a rather wicked load of 62pF in series with
>1nH and 0.3 Ohms at 400 MHz - a small patch antenna - and even higher it got
>worse.
>
>Hartshorn's 'Radio Frequency Measurements' of 1940 is still worth
>reading..........
>
>73
>
>Peter G3RZP
>_______________________________________________
>Amps mailing list
>Amps@contesting.com
>http://lists.contesting.com/mailman/listinfo/amps
>
>
>
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
|