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Author Topic: T/R Switch  (Read 2364 times)
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W7SOE
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« on: November 13, 2006, 05:15:13 PM »

I will be setting up my AM station, my first, in the next few weeks.  K4KYV was kind enough to send me his T/R relay sequencing scheme, very clever!  My station will consist of a E.F. Johnson Viking II as a transmitter and either a SX-42, R-388, or Heathkit SB-300 as a recever, whichever is working first!

Looking at the schematic of the T/R sequencer it appears that it does not switch the antenna and transmitter directly, rather it they would require their own relays.
So it seems to me that I should replace the HV (plate) switch of the Viking II with a relay that is driven by Output One of the sequencer.  (Or, I suppose, that I could place the relay in parallel with the plate switch as then I could still switch it on manually)

Output Two would drive the antenna relay.  Does this have to be a special relay?  I keep hearing of these Dow Key devices....

I plan on having the three sequencing relays, the antenna relay, and a 28V switching supply in one box with connectors on the back for TX, RX, antenna, and terminals to connect to the TX relay that will be in the Viking II.

Does this seem reasonable?  Sanity check please...


73

Rich

W7SOE
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n3lrx
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« Reply #1 on: November 14, 2006, 12:22:45 AM »

Not sure how the receivers mute but on the back of the Viking there is a ceramic Xtal socket, (HC/3 type) during Xmit there is 120VAC on that socket. Provided you have a 120VAC coil on the relay you could use that as your keying source for the relay.

That's provided that Don's contraption is not something that requires tinkering with the plate switch. As for the receivers some have a mute connection on the back, some are make connection to mute, some are break connection to mute.. Depends on your receiver. I just used a simple 120VAC DPDT relay on my Viking, Receiver ant. is connected to the normally closed position on the relay, Transmit on the Normally Open connection. The antenna is connected to the floating contact. When the relay is energized it switches over. For receiver mute you use the other side of the relay and make or break connection on transmit depending on the receiver.. No fancy delays though.. You hit the plate switch and for a millisecond or two you're dumping into no load. But once the relay clamps you're connected.
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Rob K2CU
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« Reply #2 on: November 14, 2006, 12:36:36 PM »

Most vintage rigs required an external antenna changeover relay. The Dow Key relay provided a clean way on handling the RF since it had coax connectors built in. IF you can fit a multipole relay under the chassis of your transmitter without mucking things up that's great. My 1960's setup used a Dow Key relay that had additional DPDT switch contacts. I had a transmit/Receive switch on my homemade station console. Transmit would send 110 VAC to the coil of the Dow Key. One of the auxillary contacts on the Dow Key worked the mute line to the receiver. The other closed the circuit for B+ to the transmitter.  It was simple.  When I wanted to add PTT, I added a low voltage DPDT relay. The PTT or T/R switch would energize the 24 VDC relay. One of its contacts would power the Dow Key. A second contact was added to the transmitter B+ path, so the B+ went through both relays. As soon as the PTT was released, the first relay would depower the xmiter and the Dow Key. The slight delay of the two relays provided the function of not powering the transmitter until both were closed, yet depowering as soon as the first was opend. This ensured that the transmitter never tried to put power into an open line.

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W7SOE
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« Reply #3 on: November 14, 2006, 05:55:42 PM »

I have a beautiful 24V DPDT relay here, 10A per contact.  I plan to run the contacts in parallel and install it in the JV II transmitter to switch the plate voltage on and off.  I don't think there is room under there for the antenna switch-over relay.

So the setup (right now) is the plate voltage relay in the transmitter which is controlled by one of the three sequencer relays.  The sequencer relays (and the antenna crossover relay) would be in an external box.   Hmmm, better make a picture....  attached.

73

Rich


* sequencer.jpg (34.12 KB, 960x720 - viewed 268 times.)
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ve6pg
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« Reply #4 on: November 16, 2006, 08:56:22 AM »

..I JUST USE SIMPLE 117 VOLT RELAYS...ONE PER TRANSMITTER...VOLTAGE FROM THE BACK OF THE APACHE, VIKING2, OR DX100 KEY THE RELAY, AND SWITCH ANTENNA FROM RECEIVE TO TRANSMIT, AND MUTING THE NC300 AS WELL...NEVER HAD A PROBLEM...TIM...SK..

* Antenna Relay.doc (35.5 KB - downloaded 121 times.)
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...Yes, my name is Tim Smith...sk..
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