[aprssig] Return loss bridge

[Stephen H. Smith]

Bob Donnell wrote:
> Hi Scott,
>
> Minicircuits has a 10 dB coupler with some decent directivity
>
> http://minicircuits.com/pdfs/ADC-10-4.pdf
>
> The first trick will be to get it hooked up with connectors - but that was
> with a very quick search, and it covers a lot wider bandwidth than you asked
> for.
>
> 73, Bob, KD7NM 
>
>   

This is exactly what I use!  I have the predecessor through-hole-mount 
version of this device with internal termination.  It's in a case about 
1/4" wide by an inch long by about 1/2 inch high. 

I have 2-inch pigtails of RF-142 (stiff teflon coax the diameter of 
RG-58) soldered directly to the in and out pins of the main line, with 
the braids soldered to the metal case.   I have a male BNC plug on one 
end of the main line and a female in-line socket on the other.    The 
side channel comes out to about a foot of skinny teflon coax about the 
diameter of RG-174 terminated in a mini-BNC male connector.   

The teflon coax is stiff enough that I can plug the male plug directly 
into the panel BNC socket of the tracking generator in my IFR-1500.     
You then connect a standard BNC-BNC cable between the other end and the 
device under test.  The foot-long mini-coax pigtail then plugs neatly 
into the spectrum analyzer RX input.  

Works perfectly and the entire assembly stows easily in the test lead 
storage area in the IFR's lid.     I actually built TWO of these devices 
with two different frequency-range-rated couplers  -- one for 115-1000 
MHz and a second one for HF work using a coupler rated .1-50 MHz. 



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Stephen H. Smith    wa8lmf (at) aol.com
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