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Re: Topband: wide band noise generator

To: TopBand List <>
Subject: Re: Topband: wide band noise generator
From: Art <>
Date: Thu, 21 Aug 2008 18:57:01 -0600
List-post: <">>

dick-bingham wrote:
> Regarding ===>
> "Message: 2
> Date: Wed, 20 Aug 2008 09:32:56 -0700
> From: Tree <>
> Subject: Topband: Wideband noise source
> To:
> Message-ID: <>
> 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 
> Snip
Tree -- Or you could just buy the *N-gen Wideband Noise Generator.(100 
kHz - 500 MHz) *from Elecraft. For $39 it does not seem worth the effort 
to make your own. This one comes on a classy PC board, assembles in a 
couple hours.

Beyond spending lots of money there, I have no pecuniary interest in 
Elecraft. Just a happy user. Looking forward to this winter with my K3.

73 Art
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