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AM Detector for Collins KWM-2




 
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Author Topic: AM Detector for Collins KWM-2  (Read 3196 times)
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ve1hd
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« on: November 22, 2009, 09:38:25 PM »

Does anyone have a circuit for an AM detector for a Collins KWM-2. Preferably one that could be sonnected without mods to the appearance of the radio.

Thanks ... 73 ... Clarence ... VE1HD
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K3ZS
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« Reply #1 on: November 23, 2009, 10:05:16 AM »

If you had an AM detector, it wouldn't sound good on AM because of the SSB bandwidth.   I have a Tempo One and a National NC-200 transceivers with the AM mode, but no wider bandwidth on the IF.  They transmit OK but sound like crap on receiving.
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N2DTS
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« Reply #2 on: November 23, 2009, 10:43:53 AM »

Not sure how you would do it on the kwm-2, you have to consider the agc.
For some receivers, you can take the IF output and build a detector, or use a sync detector like the Sherwood unit.
From memory, the kwm2 is ssb only, unlike the 75s series which had AM receive, with provisions for a wider AM filter.
At 2.7kc, the KWM2 would only do one sideband.

While I like the look and build quality, the kwm2 series was really poor on cw (they send an audio tone!) and no AM at all....
Receiver specs are very poor in every respect.
The top Collins ham receiver seems to be the 75s3b at number 37 on the list, BELOW some heathkit receivers!!!!

http://www.sherweng.com/table.html
 
Brett



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The Slab Bacon
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« Reply #3 on: November 23, 2009, 10:45:38 AM »

You could just stash a switch somewhere to cut off the BFO.
But if I remember correctly the kwummy-2 has a 2.1kc IF filter.
You would have to slope tune it to get anything that even remotely sounds like AM audio.
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K3ZS
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« Reply #4 on: November 23, 2009, 03:46:38 PM »

I think there is a Q-Multiplier output built in on the KWM-2.   An external IF amp, detector and audio amp could probably be connected there.   Maybe just an old AM radio could be used.   
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IZ0MFI
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« Reply #5 on: December 01, 2009, 12:53:11 PM »

Hello guys,
My name is Marco and im writing from Rome Italy, I'm a Collins rigs lover but i've added the AM mode in mine cool benchlab KWM-2  Grin.
I replied the 75s3 AM demodulator and can be achieved using one of dual diode in the AGC detector and few AB resistors and CornDub mica caps. I using a 4 Khz mech filter from '390 urr.
You can see here:
http://www.youtube.com/watch?v=_ZXxkYvzIZ8
or here the internal pictures:
http://groups.google.it/group/boatanchor-roma/browse_thread/thread/78d3dc0aa46ef547#
It's seems very good expecially in the crowded 40 mt band.
'73 Marco
 IZ0MFI
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W1BCC
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« Reply #6 on: March 14, 2020, 09:12:09 AM »

I realize it's 11 years later, but this thread is the only hit from a Google search.

Recently I acquired a 1961 KWM-2 which has a AM/SSB switch mounted under the cover.  Doesn't appear to be home brew as construction, bracket and lettering look professional.

It does work in the AM position.  Listening to a local AM 75m net.

No idea how it works. 

If anyone has seen/heard of this mod, please let me know.

73,

--Brad  W1BCC


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WBear2GCR
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Brrrr- it's cold in the shack! Fire up the BIG RIG


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« Reply #7 on: March 14, 2020, 09:39:15 AM »


What does the "DX Adapter" do??
EDIT: ok, found that, allows split frequency operation...

Are you showing us that or the copper box??

Maybe a wider shot, if it is the copper box... also what is the tube?
Any markings on the box??
How is the AM mode enabled?

                       _-_-bear
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_-_- bear WB2GCR                   http://www.bearlabs.com
W1BCC
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« Reply #8 on: March 14, 2020, 10:17:23 AM »

Thanks for responding.

T and R crystals installed in the "DX Adapter" are both 8677.5 (14.2).  The sockets are jumpered to the 1C and 2C crystals.  As you might see in the pics, it has an on/off switch.  Once the low receiver sensitivity issue is corrected (I hope), I'll do some testing.

Thinking that maybe the original owner had a stash of 20m crystals that he would swap in and out?

The "AM/SSB" switch is mounted to the bracket which supports the "DX" adapter. 

The copper plated box is part of the Waters Notch filter/Q-mulitplier mod.  Again, can't test yet due to low rx sensitivity.

BTW, it also has the Waters EVT which seems to work quite well.

Had to have been a seriously cool rig back in 1962.....


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WBear2GCR
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« Reply #9 on: March 14, 2020, 11:00:57 AM »

The AM/SSB bracket is homebrew.

You'll need to trace the wires and see what is being done. Write out the schematic.
Or find the old article that it may have followed.

Be sure to check all of the tubes.

The relay is/was a known issue - cleaning the contacts properly may restore
the operation.

Does it have a calibrate position?
How does that work? Normal readings, or low?

Look at the schematic and note where that injects.
Try it, of course, on all bands.

You can follow that CAL signal down the tube chain with a scope and find out
where the level drops off...

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Patrick J. / KD5OEI
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« Reply #10 on: March 15, 2020, 11:25:35 PM »

If you had an AM detector, it wouldn't sound good on AM because of the SSB bandwidth.   I have a Tempo One and a National NC-200 transceivers with the AM mode, but no wider bandwidth on the IF.  They transmit OK but sound like crap on receiving.


The KWM-2 I had long ago was ok on AM voice but it was before I was spoiled on any kind of natural sounding audio for that. It'll never sound like an SX-28! Didn't have that mod either.
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