Re: {Collins} Directional Coupler Problem

Upon closer inspection of the innards, I find two components not shown on
the schematic I got from the archives. One end goes to the junction of R3, R5
and L1. The other end goes to ground. There is a twin brother at the other
junction (R4, R6 & L2). They look like old style Tantalums, complete with
little white particles on them.

And, upon even closer inspection, one has a hole blown in it !!

So, I think the first order of business is to identify the mystery component and
replace both of them. Then I'll retest and report the results.

Anyone have a schematic showing these two parts ??

Thanks, Dick, W1KSZ

On 5/20/2015 8:36 PM, Bill Carns wrote:
Q2 2005 Signal had a great article by Rod Blocksome of Collins Radio
(Rockwell Collins) on how to calibrate the 312B-4 (or any Collins Wattmeter
using a Bruene Coupler).

This is the first step..  It sounds like someone has been tweaking on it..
Start with the recalibration and then let us know what you have achieved -
or what the status is.
It is possible that someone has over-stressed the coupler and that the
diodes need replacing..
Recal first, and if you can't get it aligned, then start by replacing the
diodes and recal again Dick.


Bill Carns, N7OTQ (Trustee K0CXX)
Past President, Collins Collectors Association
Founding Board, Collins Radio Heritage Group
Editor, Signal Magazine
Wimberley, TX
512 618 2762  (Cell)
512 847 7010  (Home)

-----Original Message-----
From: Collins [] On
Behalf Of Richard Solomon
Sent: Wednesday, May 20, 2015 9:01 PM
To: Collins
Subject: {Collins} Directional Coupler Problem

I picked up a nice looking 312B-4, was touted as working ... but the Power
Measurements are wacky.

Now, I have an HP Power Meter that just came back from the Cal Lab so I am
confident my power readings are OK.

Now, I put 110 watts (@ 21 MHz) through the coupler and get the following

Forward: 200 Watts   reads around 80 Watts
                2,000 Watts  reads around 60 Watts

I reverse the coax cables to read the Reverse Scale.

Reverse: 200 Watts  reads around 40 Watts
               2,000 Watts  no reading, nothing

I checked the resistors in the coupler, reading from the terminal strip
(first I disconnected the leads) to the junction post in the coupler. I used
a cal'ed Keithley 196.

All readings were within a few %.

Any ideas what can be wrong ??

Thanks, Dick, W1KSZ

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