Update on vintage station change over circuit

[w1vtp]

Here is the latest in documentation for the vintage change over circuit.  I added some noted into the PDF so let me know if you do not see them.  The changes are necessary because I want to use this circuit with my Viking I and it does not have an internal circuit for muting a receiver on transmit.

Al

[steve_qix]

I had a bit of trouble following everything, but I'm gathering the delay relay keeps the RX muted and ANT relay in the TX mode for some number of milliseconds after you go to receive?

That's pretty what I do with my "master" shack T/R system.  Everything goes through this system - all transmitters are receivers.

When going from RX to TX, the ANT relay, RX mute, all RF drivers and related turn on.  100ms later the TX enable circuit (relays) are energized and enable transmitters.

When going from TX to RX, the transmit HV and other transmit circuits are de-energized, and 250ms later the drivers, RX mute and ANT relay all de-energize and everything is in RX mode.

Any sequencing within transmitters themselves is in addition to this system.  I have used this for at least 40 years - built it when I was in college in the early '70s.  In my opinion, a must for all shacks that use independent transmitters and receivers.

[w1vtp]

All this accomplishes is that the Collins / EFJ Viking transmitter is delayed from transmitting for an adjustable amount of time.  There are better circuits out there than mine.  Some of you might recall that I am having some problems with the 32V1 arcing when going from RX to TX.  This was implemented to eliminate the possibility that there was a momentary high VSWR presented to the 32V1. 

It also brings to mind this neat adjustable delay relay that some the newer AMers might not be aware of.  The update served to publish my notes for anyone who might be interested.  This does not apply to my class E station - only the vintage station be it the 32V1 or the EFJ V 1, 75A2 or SP600.

[N2DTS]

I just key and unkey everything at once, except the step start relays power the screen circuits.
I have not had a problem with anything in 30+ years, am I missing something?

[steve_qix]

I don't know about missing something, but you got lucky I guess.  Back in my tube days, when I started running real power with plate modulated transmitters (1kW DC input), I would notice arcing at the T/R relay - indicating there was still some power coming from the transmitter when going from transmit to receive.

It is just not possible to switch a plate modulated transmitter instantly off.  There is energy stored in inductors (like the mod transformer/mod reactor) and capacitors that has to go somewhere.

A graceful transition from transmit to receive takes some measure of time.  There should be a predictable load on the transmitter during this transition.  This dictates some form of delay from transmit to receive.

Now, there are LOTS of kinds of transmitters that CAN be switched off pretty much instantly.  Grid modulation, linear amplification of a low power transmitter, pulse width modulators and pretty much anything that doesn't use mod iron can be so switched and there will likely be no problem of stored energy that needs a place to go.

And of course one can take special measures within the transmitter itself such as loading the mod transformer or spark gaps, etc. etc. etc. that certainly help.

My personal preference is a graceful, predictable transition from transmit to receive and visa versa.

[N2DTS]

Sounds like a good idea then.
My rigs can run up to 1kw carrier output and I have not had problems.
My TR relay is a giant ceramic base DPDT contactor, its been the same for 30 years.
The only issue I notice is the sdr plays my TX audio for 1/4 second after I unkey.
Due to usb delay it lives in the past...

The DPDT part grounds the RX on TX and grounds the TX on RX.

 

[KA2DZT]

My xmtr uses a step-start to power up the HV.  Well it's a bit more complicated than that.  My xmtr runs at two power levels.  One is a 6146 modded by 6550s.  Second level is a 813 modded by 811s.  The drive comes from the 6146.  The xmtr can move from one power level to the other by moving a few switches on the front panel.  A single toggle switch controls xmit and receive in both power levels.  A single DowKey relay controls the antenna line and mutes the receiver by way of the extra contacts on the relay.  A B+W antenna switch which is mounted on the back of the xmtr switches the 813 in line.  The B+W switch is controlled on the front via a long shaft.  On this shaft is a micro-switch which closes and activates a number of 6v relays.  These relays do a number of different things. Shut off the 6550s. Drop the B+ on the 6146 from 650V to 300V.  Turn on the 813 and 811s and audio driver for the 811s.  The same low level audio chain is used for both modulators.  Make ready the HV supplies to come on (via the step-start) the next time the xmit toggle switch is turned on.

Anyway, just a brief description on how my HB rig works.  I don't use any delay timing on anything except the step-start for the HV supplies.  I haven't had any problems with anything.

Steve mentioned the back EMF when the HV drops.  I use a 50Hy reactor for the 813/811s.  I think, because the HV remains connected, the filter caps absorb any back EMF.  This also hasn't been a problem.  Any forward transients (if any) are just absorbed by the final.

Fred

[N2DTS]

Wow, that is cool, run the exciter or the big rig with the flip of a switch!

My 32V3 used to arc the plate tune cap when run at 700 volts, but the cap was pushed off center by its shaft, I have to get really crazy to arc it since setting the shaft to pull on the cap a bit.