[Amps] hit a wall on bi-directional couplers

[m.ford]

----- Original Message ----- 
From: "Dan Sawyer" <dansawyer at earthlink.net>
To: "amps" <amps at contesting.com>
Sent: Saturday, November 19, 2005 8:58 PM
Subject: [Amps] hit a wall on bi-directional couplers


> All,
> 
> I have hit a wall on bidirectional couplers for HF. I have breadboarded 
> the bi-directional portion of the following attached bi-directional 
> coupler circuit. It appears in principal to be the same as the circuit 
> in the arrl antenna handbook.

Hello again Dan,
    I have not seen the circuit you refer to in the handbook. My latest
copy is 1977.

> 
> http://www.ramseyelectronics.com/downloads/manuals/PM10DC.pdf
>
The circuit shown in fig. 1, page 5 looks like a 180 degree hybrid.

> I did not terminate either coupler output, I simply sampled them for 
> voltage with a high impedance scope probe.

Hybrids are difficult to construct. Symmetry is a must.
It is wise to use attenuators on the output ports when making
measurements with them.

   The net net is there is no 
> difference between the outputs and they are both high, about 3 db down 
> from the input.

If you terminate port A and feed port B you have a 2 way power divider
that will give you equal outputs at D and C  and they will be 3db down.
Plus insertion loss.

   I did not use a 'binocular' transformer but used two 
> tube types in the same configuration.  I was very careful to wind the 
> transformers exactly as described in the text.  The feed through is a 
> piece of copper wire centered in the transformer by an insulator. The RF 
> output is terminated in 50 Ohms.
> 
> I would appreciate pointers, advice, links to primers, or links to 
> alternatives.  Thanks - Dan kb0qil
> 

If what you are really looking for is a bi directional coupler for your
vector voltmeter I would suggest a Model CH-130 made by ANZAC.
The coupling is 30db but it will handle 500 watts and covers the entire hf band.
Must be one out there somewhere. 

Mike k1ern