Date: Wed, 20 Aug 2008 09:32:56 -0700
From: Tree <email@example.com>
Subject: Topband: Wideband noise source
Content-Type: text/plain; charset=us-ascii
Well - my 2nd parasitic element is online.
And now - I have to figure out how to tune this sucker. :-)
One tool that I think would be useful is a wideband noise generator of
some kind. Occasionally, I can use some distant power line noise, but it
is only in one direction.
Having some kind of wide band noise generator would allow me to quickly
find the frequency where I have the best front to back ratio.
Anyone have some experience with this?
The good news is that in one of my two directions, I was seeing almost 5 db
of gain!! I have to get things tuned to get that in the other direction.
The method of measuring gain might be of interest. I bought a used radio
direction receiver on ebay. I got mine for about $25. It has a loop
antenna on the top of it that has a nice null for DF purposes. You might
remember seeing one of these in the old Heathkit catalogs.
It also has a very sensitive signal strength meter - and you can adjust
the reading to a reference point. Then you can have someone throw the
swith back in the shack and adjust the power setting to get the same
reading on the meter. Then, you can calculate your gain (or F/B) in db
by comparing the power level difference. I was doing this at a distance
of about 1.5 miles with 10 watts power.
Tree N6TR ..."
I would suggest building a simple wideband noise source good for any
reasonable band of interest. Examine the wideband noise circuit used by
noise-bridge impedance measuring devices (one in HR back in the 80's comes
to mind) for generating a wideband noise source. Amplify this noise and
apply it to your source antenna.
Use a doubly-balanced mixer and power it with 10dBm-worth of LO at the
center frequency of interest. Then insert broadband noise into the IF-port,
connect the RF-port to an antenna and you're good-to-go...
You could also build a 4096-long PRN generator with a 250KHz clock to
modulate the IF-port to make a DSSS generator... This should provide a
reasonably "flat" output over +/-100KHz.
Dick - w7wkr
Topband mailing list