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Author Topic: QSK T/R Switch for Boat-Anchors  (Read 25317 times)
KG6YV
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Posts: 593




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« Reply #15 on: October 27, 2010, 01:14:51 PM »

SInce this is the boat anchor forum,

What about recreating the E.F, Johnson T/R switch which was very popular in the 1960's.  They were an electronic
T/R switch that used two tubes I believe.  The antenna remained connected to the transmitter and the tubes switched out the receiver electronically when they sensed power from the transmitter.  They were very fast.

Of course one can be built with modern components but recreating a tubed version like the JOhnson might be fun and fitting for a BA station.

Greg
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N2EY
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Posts: 5063




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« Reply #16 on: October 28, 2010, 03:28:23 AM »


What about recreating the E.F, Johnson T/R switch which was very popular in the 1960's.  They were an electronic
T/R switch that used two tubes I believe.  The antenna remained connected to the transmitter and the tubes switched out the receiver electronically when they sensed power from the transmitter.  They were very fast.

That can be done; the manual for the EFJ switch is on the BAMA site. There were many homebrew designs for electronic TR as well. But it is only part of the solution.

Running full QSK with BA gear requires a suitable transmitter and a means of muting the receiver. All the TR switch does is keep the transmitter's RF out of the receiver.

Under some conditions, electronic TR switches can generate TVI, and if used with a very good receiver the performance of the receive system is made worse by the TR switch. Relay systems don't have those problems.

73 de Jim, N2EY
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KE4JOY
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Posts: 1418




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« Reply #17 on: October 29, 2010, 02:19:27 PM »

Really well done article. I'm getting ready to build one of these.

I'll have to admit Ill be excited to put an old SB303 into a more usefull service. (I only have one antenna)

Quick questions.

In reviewing the parts list I have to ask, what are the two IC sockets at the end of the list for?

When looking at the photos I noted a seemingly extra screw on the back just below and to the left of the 'rcvr' so239.

Lastly what gauge wire for the connections to the SO239s ? Looks like 14 stranded.
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AD5X
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Posts: 1621




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« Reply #18 on: October 29, 2010, 05:40:07 PM »

The IC sockets are for the relays.  Of course you can solder directly to the relays, but I like use sockets.  The extra screw(s) fill holes as the box was previously used for another project.  And 20-gauge wire is fine for the interconnects.

Phil - AD5X
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KE4JOY
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Posts: 1418




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« Reply #19 on: October 30, 2010, 05:31:18 AM »

First thing on the list (after the relays) is a pair of machine pinned relay sockets.

Last thing on the list is a pair of IC sockets.

I dont have the list in front of me but thats the way I remember it.
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AD5X
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« Reply #20 on: October 30, 2010, 10:29:20 AM »

Sorry.  Dubplicate.  Either part number is fine.

Phil - AD5X
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KE4JOY
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Posts: 1418




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« Reply #21 on: October 30, 2010, 01:35:13 PM »

I have some IC sockets in the parts bin. Many thanks !
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KE4JOY
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« Reply #22 on: November 07, 2010, 11:27:25 AM »

Learn from my mistakes  Cheesy

Just a little heads up to hopefully avert a little grief for anyone building this.

The little Omron relays coils have a polarity as mentioned in the article.

The relay case has a schematic screened on top of it indicating the polarity. This schematic is a MIRROR IMAGE (fine print says bottom view).

So don't do what I did and get it all wired up, transistors working, output to leds, put it in the case and wire it up plug in the relays and ... nothing. Only after I looked at one of the relays under a magnifying lens did I see the 'bottom view'.

I had wired the relay coils backwards. Did not damage them but now I have to disconnect all the panel jacks etc and do some rewiring on the bread board. I was ready to screw on the cover  Tongue
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K4ELO
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Posts: 60




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« Reply #23 on: November 11, 2010, 06:02:21 PM »

Nice article Phil and a good project.

I never did get around to building the digital T/R switch I designed and we corresponded about a couple of years ago.  Got way overwhelmed with computer project work/travel and never got around to building it.  Maybe when I retire next year Smiley.  But yours is a lot simpler and that makes it more elegant to me.

But that does remind me of a large (maybe 5"x6") homebrew vacuum relay T/R switch I purchased from someone way back in the early 1970's.
It used some kind of very large (probably surplus) vacuum relay, but it did handle a lot of power.
I remember using it with my Drake 4B line and it switched the L4-B at a kw with no problem.  Nice qsk at qro, but I did have to add a simple single transistor receiver muting circuit to it.
I think it's still hanging around in my junk box somewhere and now that I have some boat anchors again, I'll have to dig it up.

73
Wayne
K4ELO
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KE4JOY
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Posts: 1418




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« Reply #24 on: November 19, 2010, 09:24:53 AM »

Well I basically stripped the boards and started over with the proper polarity on the relay coils.

It works a treat. I was a little hesitant at first as I don't really have any way to 'test' the sequencing of the relays but bit the bullet and put the RF to it and no problems.

I'm using it with a SB303 which is a solid state receiver and so far haven't cooked its front end nor have I noticed any degradation in sensitivity.

Anyhow thanks for the very enjoyable and usefull project!
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