T/R switch construction

[Opcom]

Now that the ol' Tucker is making RF properly, time to build a T/R switch.

First thing, the RF switching - should a vacuum relay be used for this and/or why?
I thought about a regular 600VAC 20A contactor to connect the TX to the coax, and a small DPDT relay (like a 10A job) that would control it could alternately connect the RX to the coax and short the RX input when in TX mode.

Next, what is the scheme, without using semiconductors, to make relays activate in one order while activating, and let go in reverse order when de-activating. like so:

key: 1 on - 1+2 on - 1+2+3 on - 1+2+3+4 on (on the air)

unkey: 4 off - 3+4 off - 2+3+4 off - 1+2+3+4 off (receive mode)

RC timing will do.

There has to be a known relay logic for this kind of program, that is, the first electric computers used to be made of relays, so..  

[KC2ZFA]

maybe you can daisy-chain the simplified k4kyv method I recently referred to here: http://amfone.net/Amforum/index.php?topic=29412.msg228076#msg228076

[ke7trp]

You can use the relays fine. No need for vac relays.  What you are needing is a sequencer.  Are you going to use an external Exciter or does this rig have a built in exciter?

Mine is a project box that contains Three SO 239s. One for ANT, one for REC and one for the RF Deck. 

It also has RCA jacks for the PTT, Exciter keying,  and two spare RCA jacks, one NO and one NC for muting of Recievers and or other uses.  There is also an RCA jack that switches the coil on the HV relay for the plate supply.

The inside is very simple. A relay, some big diodes and a large Capacitor for time delay.  Its about $10 to $20 in parts.
C

[WQ9E]

What all are you switching?

For some high power rigs I use a vacuum relay with an electrolytic cap in parallel with the coil for the actual antenna transfer and a standard cube relay to key the exciter and mute the receiver.  The vacuum relay is faster than the standard relay on make so it won't hot switch on make.  The capacitor across the coil provides a slight delay on break to prevent hot switching on PTT release.  Depending upon what else you need to do any other active sequencing may not be needed.

[Opcom]

switching the antenna between the transmitter and the receiver, wish a rating of 6KW PEP, actual level will be legal limit. Wish to short/GND the receiver's antenna port before the TX begins and release this after it ends.

switching a 400-1000V screen voltage at 150mA or less.

switching some 12VDC and 120VAC relays and 120VAC primaries, 5-6A, (no issue there)

[WQ9E]

Patrick,

With that setup,  you should be able to start with one relay controlled by your PTT switch.  This is the relay that will ground the receiver input with one set of contacts.  Contact set two will control coil voltage for a DC coil vacuum relay for antenna switching and this relay should have a small electrolytic cap across the coil to provide a short delay on release.  Since it is a vacuum relay make time is very fast and it will switch before the remaining standard relays controlled by your main relay.  Contacts 3 and 4 should be used for the 120 VAC and 12 VDC feeds to the remaining relay coils including the one that handles the screen supply.  If you need to switch the screen supply high voltage output (instead of the input) you will need a HV relay if you go to the high end of your expected range.  But at around 700 volts or less a regular relay with 240 volt AC rated contacts and a snubber (series resistor and capacitor) across the contacts will be fine.  Gonset used a relay with snubber for the final HV feed in the G-76.

How is your plate supply handled?  You need to make sure that there is no chance of the screen being powered up without plate voltage supplied.

Is this a class C plate modulated setup?  If the final operates in linear mode then a regulated screen supply with protection scheme like that used in the G3SEK tetrode board scheme is a good idea.

[N4LTA]

Ever consider an Ardinuo Uno board for $25. Very easy to program and many I/O to sequence the relays.


Pat

[KA3EKH]

I built up a separate panel that has control of the T/R relay  in the transmitter the  panel works a second relay to switch the receiver input to ground and interrupt the receiver audio output and also hold the T/R relay in the transmitter in for about half a second after the PTT line changes because I use the interlock circuit of a converted broadcast transmitter to control the plate of the transmitter and being that the filters in the transmitter still had some voltage in them did not want the transmitter switching from the antenna too soon. Don’t know what transmitter you will be using and how you will be controlling it but assuming being the “Bunker” it wont be some pettily little 50 watt rig or some rice box so do it with relays, capacitors and maybe time delay relays. Microcontrollers or store bought sequencers, come on man! You have an image to uphold. Let me know if you need any 24 VDC TD relays or 120 VAC stuff, have lots of plug in stuff with sockets.
RF

[Opcom]

I built up a separate panel that has control of the T/R relay  in the transmitter the  panel works a second relay to switch the receiver input to ground and interrupt the receiver audio output and also hold the T/R relay in the transmitter in for about half a second after the PTT line changes because I use the interlock circuit of a converted broadcast transmitter to control the plate of the transmitter and being that the filters in the transmitter still had some voltage in them did not want the transmitter switching from the antenna too soon. Don’t know what transmitter you will be using and how you will be controlling it but assuming being the “Bunker” it wont be some pettily little 50 watt rig or some rice box so do it with relays, capacitors and maybe time delay relays. Microcontrollers or store bought sequencers, come on man! You have an image to uphold. Let me know if you need any 24 VDC TD relays or 120 VAC stuff, have lots of plug in stuff with sockets.
RF

Well I do not know about an image to uphold. I'm never on the air, the big stuff is not up, and I have so little time to solder or wrench. No image can come from that! There is large size stuff here but not as large as some. But true, no 50 watt stuff and SS rigs except as an exciter.

I am trying to do this without adding solid state items to the transmitter. I know I could use some TDRs but it should be possible to do it as shown in the attachment, thanks to some advice here. Now it looks like not so much sequencing and the huge number of contacts because everything is separate.

The transmitter is not really a transmitter, it is an RF amp and a modulator. Therefore there is an exciter to key and receiver to mute and protect. Also a spotting function for the VFO, as it will have its output shut off during receive (another set of contacts) and the drive amp, a broadband solid state item, it will be keyed via its 12V power supply. Plus the speech amp needs muted so it can't drive the modulator grids. I can break a C.T. or kill screens for that.

The "transmitter" has been keyed by closing the plate relays and screen relay together. This makes lots of green flashes in the relays so although I like that I have to be practical and find a way to just key the screen grid of the class C stage, and short the modulator during receive so any audio won't be passed to a no-load situation.

There is screen protection via a latching relay that is released when the G2 current is too high. It opens the screen power supply HV transformer.

A couple of 4PDT relays with the capacitve time delay as previously shown could be added to what has been drawn.