[Antennas] Return Loss Bridge Questions

[Ronald KA4INM Youvan]

   Your assumption is quite correct, it is simply a matter of the sensitivity of 
the indicator device.

   Use a good 'scope and 5 or 10 mW from a sweep generator might be fine, if 
it's a bridge made with ferrite beads etc.   If it's made with resistors 100 mW 
may not be enough.
   You can make a HF only return loss from a QST article of 5 or 6 years ago, I 
built one and it works fine, it is barely useable on 2 meters.
   VHF and above a directional coupler works just fine.  I use one with a 1 mW 
generator tracking a spectrum analyzer, with NO detector.

> 	I've run across an return loss bridge design I'm interested in and 
> have a few questions those of you who are of the engineering mind 
> might help answer.  I'm also curious in the design generally.

> 	The bridge information is at:

> 	http://www.pollak.sulinet.hu/elektro/hidak/bridge/how_to.htm

> 		My specific question is regarding minimum drive.  The author states 
> that the minimum drive in 100 mw, with typical drive of more like 1 
> watt.  I'm more interested in an instrument that can use output 
> levels more typical of a good signal generator (I don't want to 
> radiate more than I have to) especially on frequencies outside the 
> ham bands.  

> 		What determines minimum drive?  Is it simply a matter of the 
> sensitivity of the indicator device, or is there something else at 
> work here (probably insertion losses?).
-- 
        73 (= Best Regards) de: Ron ka4inm@tampabay.rr.com
     100% Slack. since July, 1997 (still free!) SENT D&T are UTC
        Visit my HAM Web SITE at: http://www.qsl.net/ka4inm