[Wswss] RE: [Mw] Re: Simple 432 MHz return loss bridge

[Baker, Donn B]

Hi Cliff,
You might look at Paul Wade's article in the Feb '95 issue of QEX, "A UHF+ VSWR Bridge."  Small, simple, works well, well beyond 450 MHz.

Note that this is NOT a "sampling type" SWR detector, or directional coupler, as you more or less described... you can't put power (even signal generator levels) through it.  You connect your unknown, a reference load, and apply RF excitation.  It then gives a DC output voltage proportional to the mis-match between your unknown and the reference.

73 Donn
WA2VOI/0

> -----Original Message-----
> From: microwave-admin at lists.valinet.com
> [mailto:microwave-admin at lists.valinet.com]On Behalf Of Cliff 
> Buttschardt
> Sent: Wednesday, January 05, 2005 7:48 PM
> To: Microwave Reflector; WSWSS at mailman.qth.net
> Cc: Weak Signal eMail Remailer
> Subject: [Mw] Re: Simple 432 MHz return loss bridge
> 
> 
> Hi all.  Seems some simple problems can get awfully complex.  
> I would like to
> build a small signal----that is signal generator 
> operated----return loss bridge
> for the 420 to 450 band.  Most of the publications show 
> complex microstrip
> designs.  I visualize two panel mount type "N" connectors 
> spaced by the width
> of a BNC panel mount connector, that is about one inch, all 
> soldered together.
> Then possibly a #16 wire between the type "N's" and a ferrite 
> bead suspended
> between the two, with pickup loop of teflon coated wire of 
> say #28 size.  The
> loop is terminated on one side with a fifty ohm resistor.  
> I've used ferrite 
> #77 material which should be good to 440 MHz, but maybe this 
> is wrong.  
>      The best directivity I can get is only 8 db or so using 
> a spectrum analyzer
> as a detector.  Is this the problem?  From the RSGB handbook 
> is appears a high
> impedance detector should be used but so far that has not 
> improved things.
> There has to be a way of putting a small device such as this 
> between a signal
> generator and an antenna rather than a complex directional coupler.  
>      If I am trying too hard that is just as valuable an 
> answer as any BUT
> HP has a small device such as this and we should be able to 
> duplicate it!!
> Cliff K7RR
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