RadioBanter - View Single Post

May 24th 06, 02:21 PM posted to rec.radio.amateur.homebrew

wrote:
On Tue, 23 May 2006 12:48:18 -0400, (Fred McKenzie)
wrote:

In article ,
wrote:

Two caveats, rarely are RX input impedences 50 ohms and there is no
guarentee that the antenna is 50 ohms.
Allison-

Such is life. However you can assume that both are 50 Ohms and use a
resistive pad between the signal generator and the receiver when
calibrating. When making a reading, use a pad between the unknown signal
source and the receiver.

Without a sophisticated system capable of determining impedances while
making measurements, this may be the best you can do.

Fred

Yes, you can do all that and more easily. Often it means little. I
rarely use my comms as measurement recievers as I have dedicated
equipment for that. For those the available devices from Analog
devices are excellent.

For general on the air work S9 meaning whatever is mostly
convenience in aiming the antennas and even then peak is
the criteria. However I've used at least one radio where the
S-meter was so sluggish on slow AGC and so twitchy on fast
AGC that using for aiming antennas was annoying.

I'd also said for most radios I've encountered the meter even if S9
was a calibrated point the the interval between points was at best
wildly inaccurate. For that case the calibated point is at best moot
and for any measurements the ide will be to keep a fixed point as
reference and use attenuators to assign value above or below that
point.

Allison

I found the N6NB method using a VU meter with the AGC off very useful.
However using a receiver with the AGC off is unbearable. I would have
thought that a radio like the Ten Tec Orion could have easily
implemented a calibrated S meter. However without hams demanding it and
hams willing to live with the Guess Meter manufacturers wont bother.

There is a fax station in Germany running 20 kw or so, into a vertical
antenna on 13,882 or somewhere around their. Its quite useful comparing
it to the many ham stations running beams and even low power with beams.
Its also a useful propagation beacon. Its been on for years and i
wanted to measure the signal strength and compare it to what VOACAP
predicts.

In private emails some people have indicated that Winradio has a
calibration software option for their receivers. So that may be another
option. Some users have also indicated that the RFSPACE DSP receiver
likewise is quite accurate with amplitude measurements.

There are options...

Will