Re: [amsat-bb] 2.4 GHZ Antenna Bridge

["wc0y" <wc0y@xxxxxxx>]

Jesse,
I also built the S-Band bridge circuit and find it very useful.  It has been
used to tune up a 30-turn helix antenna, and as a signal source while
testing mods to a Drake converter.

The only difficulty that I had was when the ceramic base of the splitter
cracked during assembly and became intermittent.  Everything was fine when I
replaced it.

The oscillator has always been strong in mine.  I use a digital voltmeter
across the bridge to read its output.  The output ranges from a few tenths
of a volt for a matched condition to a maximum of 3.7 volts for a large
mismatch.

A photo of mine is at http://communities.msn.com/wc0y and go to the S-Band
Bridge page.

73,
Ward

----- Original Message -----
From: "Jesse Morris" <w4mvb@juno.com>
To: <amsat-bb@AMSAT.Org>
Sent: Thursday, February 22, 2001 7:05 PM
Subject: [amsat-bb] 2.4 GHZ Antenna Bridge


> Good evening to all,
>
> I'd like to compare notes with anyone who has built the antenna bridge
> that appeared in the September/October issue of the AMSAT Journal.  I
> completed mu unit last week using my own PCB layout and I may have shot
> myself in the foot.  I had a hard time keeping the oscillator going when
> the meter circuit was terminated with a current meter.   For some reason
> the circuit did not like some impeadances and he VCO would stop
> oscillating.  Removing the current meter and reseting the power would
> cause the oscillator to start again and I could measure voltage out ot
> the meter jack but the bridge doesn't work that way.  I finally
> discovered this afternoon that if I put my finger on the trace between
> the output of the oscillator and the input to the splitter the oscillator
> would run.  I tried a 5 pf capacitor to ground but that didn't work.  I
> finally decided to widen the track which was a double "L" .05 inch wide
> and about 1/2 inch long total.  I used some 1/8 inch copper strips made
> for PCB repair and made the connection about 1/4 inch wide and the
> problem went away.  Now it really works great.  You can match a helix in
> nothing flat!
>
> I used a 1/4 inch wide piece of flashing copper for the matching section.
>  I did  not attempt to shape around the PVC boom I just used it straight.
>  I also discovered that if I extended the matching section to about 1 5/8
> inches the match was very broad.  I haven't found out if that is really
> good or not.  I ran into some problems trying to match the grounded feed
> unit and had to quit before I figured out the problems.
>
> Has anyone built and used the bridge yet and if so what kind of results
> have you gotten?
>
> Thanks and 73's de Jess - W4MVB
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