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T/R for Central Electronics 600L w/tranceiver? IDEAS?




 
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Author Topic: T/R for Central Electronics 600L w/tranceiver? IDEAS?  (Read 435 times)
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WBear2GCR
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« on: November 26, 2019, 03:09:47 PM »

Looking for ideas, schemes.

Have a good (now that I fixed it) working Central Electronics 600L amp.
Want to use it with a transceiver.
It was designed for use with the CE Multi-Phase 20V exciter.

The schematic is attached.

The amp has "Input", "Output" and "Antenna".
"Antenna" was intended to be used with a receiver.
The tube is set up for grid block keying/control.
There are no "T/R" relays internal.
Stock, it would have been used with an external Dow Key relay going to
the receiver...

So, the short version of what it seems is needed goes something like this:
(working backwards from the keyed up state)
- drop exciter RF
- dump in grid block (turn off tube)
- switch "T/R relay" - transceiver for receive to Antenna (jack or coax)

Keying up:

- connect ("T/R") amp to coax/disconnect receive line from coax - transmit line to input
- send RF from transceiver
- unkey grid block (enable amp)

Of course there are a few variations on the connection scheme.
The transceiver could stay connected to the "Input" on the amp at all times,
BUT the "loop back" from the Antenna jack or alternately direct to the coax
(see schematic) must not arc, pass too much RF even on a transient, lest
the amp oscillate and/or the receiver input get fried.

Part of the circular nature of the thinking revolves around what keys what.
As in, one could "key" the amp and have that key the transceiver, or key some
sort of external relay, etc...

Assume I have Dow Key relays, and electronic T/R, suitable open frame relays...
but the idea is that the transmit jack and the receive port on the transceiver is
the same, and likely switches WAY faster than the linear or the Dow Key can.

I'd greatly prefer to NOT have to buy a uproc operated "sequencer" and really would
prefer some more basic approach. Transistors, and even some 555 timers or opamps
seem more robust to me. Don't mind building a circuit with relays...

Any ideas on how to make this go?

                             _-_-

PS. patent is attached for your reading enjoyment! Cheesy

* CENTRAL ELECTRONICS 600L schematic.pdf (691.13 KB - downloaded 31 times.)
* CENTRAL ELECTRONICS BATCHELOR COUPLER US2864060.pdf (1462.89 KB - downloaded 36 times.)
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WD5JKO
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« Reply #1 on: November 27, 2019, 07:03:38 PM »



Bear,

  The 600L is a neat amplifier, but the watts out per pound ratio is lopsided to something like 4:1. I have one, and it will do 100 watts carrier AM, and fully modulate 100%. That runs the 813 pretty hot, and cooling is marginal...needs the K1JJ Lantern glass chimney and more airflow, or something to that effect.

  About 10 years ago I did a project similar to what you are describing. The transceiver driving the 600L was the Retro75. The 600L gain is high, and the Retro75 did not like the 600L as a load. Placing a 2W 50 ohm termination at the 600L input with a coax 'T' helped a lot. Varying the 12v to the Retro75, like 10-14v would set the 600L carrier output.

  I made a relay box with two DPDT Octal based 12v coil relays. With a toggle switch, I keyed everything, non sequenced, brute force. Maybe not optimal, but effective. The whole station is intact today, but the Retro75 had a modulator problem that I never corrected. I made notes, and will look for them...Not sure if I still have them.

  If I cannot find the notes, perhaps I can reverse engineer what I did, and get back to you.

Jim
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AJ1G
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« Reply #2 on: November 28, 2019, 06:46:42 PM »

Hi Bear!  Youíve done a great job in getting what you call the 600-Elephant up and running.  I especially enjoyed your description of how you determined that a tube devoid of markings in a box of 811s was in fact your needed 812.

BTW the 600L was developed to work with the nominal 20 watt  PEP SSB output of the 20A exciter, hence the grid driven AB1 design.  I use mine with a number of receivers, including my NooElec RTL SDR with one of those octal based Potter and Brumfield DPDT relays, mine has a 115V AC coil.  It was originally configured as the antenna relay when running the 20A barefoot.  The relay coil is powered from the 20A which is equipped with a two prong AC receptacle on the rear panel that is energized when the
20A function switch is placed from standby to transmit.  This also removes the 600L blocking bias supplied from the 20A.  One set of the external relay contacts is used to switch the antenna from the receiver to the transmitter and the other set of contacts shorts the line level receiver output on transmit.  When I added the 600L amplifier I simply added it between the 20A output and the cable from the 20A to the transmitter contact of the antenna transfer circuit.  The 20A function switch controls the switching.  In CW mode on the 20A the key controls the exciterís internal TR relay, including the contacts that actuate the external antenna and muting relay. On voice modes you must remove the CW key to allow the key jack contacts to close to permit the internal TR relay to pick up.  This brute force relay keying actually works pretty well,
including on CW,!where the external antenna/muting relay is following the keying.  No clicks and a nice note.  I donít torture the relays above about 18 WPM with a straight key though.

You of course will likely need to figure out how to get the antenna to the transceiver on receive and insert the amp between the transceiver and antenna on transmit, I assume another relay will be needed, I think that is how my SB-301/401 worked with an SB-200 amplifier.

One of the receivers is the NooElec
SDR.  I have not had any issues with simply switching the antenna from SDR to the 600L output, would likely be safer to also short the SDR RF input to ground on transmit.

Good luck!  74 de Chris AJ1G


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Chris, AJ1G
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« Reply #3 on: November 29, 2019, 12:29:46 PM »

I don't know if ALL Dow-key relays are like this, but mine shorts the receive terminal when it's in the transmit position. It's a cleverly designed SO-239 connector with an internal spring that causes a short circuit to protect the receiver during transmit. That, and the isolation it affords, should be enough to protect the front-end.

As far as sequencing, most transceivers have a relay with a set of dry contacts on the T/R line to control amplifiers and such (I've had to add them to rigs that don't). If you key the transceiver itself, and let the amp just follow along, there should be no issues. The transceivers internal T/R delay would be enough. They'll be no residual RF from the amp (unless it's oscillating, which is a different problem). Even if the amp stayed keyed during receive it would have no output because it has no drive.

So what's the worry?
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WBear2GCR
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« Reply #4 on: November 29, 2019, 03:29:36 PM »

Don,

yeah, thanks for the refresh on the spring thing in the DowKey relays.
Short or not, it still lets a boatload of RF through to the receiver front end.
I've had quite a number of them in service, and they all let about the same
amount of RF through. My thinking is that the increased RF from the linear
(would it really be increased compared to my Valiant II with sweep tube modulators?)
might be more than the typical solid state front end "likes" to see.

The key to the issue for me is that it looks like I need to switch the transceiver's
coax line between the input of the amp and the antenna/output of the amp.
The "receive" condition is connected TO the ANT (or the provided "T/R" jack on the
amp).

You may be correct as far as the timing being ok as-is, but that bears more investigation.
Hot switching and insufficient isolation? I want to use a "belt and suspenders" to make sure
it won't happen, no matter what rig is used to drive the amp.
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« Reply #5 on: November 29, 2019, 08:01:43 PM »

Bear,

I'm using a TS-940S as a receiver with a DX-100 transmitter. The only thing that stands between the 100 watts output of the transmitter and the receiver is a dow-key relay. The receiver stays on during transmit and I only mute the audio from it. During transmit the receiver registers 35dB over S9. Hardly a boatload... whatever that is.

Why not make a measurement and see what you get?


Don
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« Reply #6 on: November 29, 2019, 08:41:54 PM »

If you like relays, there are plenty of 'AMF Potter Brumfield' and other time delay relays surplus. There are adjustable, fixed, activate on power-off, activate on power-on, etc etc. These interface well with standard relays and you can make quite an automatic-resetting sequencing system with them. The 120V coil ones are most common but it does not matter because outside of the control system you can use whatever you wish to close and open the sensing contacts.
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MikeKE0ZUinkcmo
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« Reply #7 on: November 30, 2019, 06:21:52 AM »

If the particular transceiver has a separate Rx only Aux antenna input option, an old Johnson 250-39 T/R switch would work.  

Mine is inline ahead of the antenna tuner, with the receiver output port feeding a distribution amp, so regardless what transmitter/amp I'm using, all the receivers are "safe".

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« Reply #8 on: November 30, 2019, 10:06:52 AM »

Bear,


I'd greatly prefer to NOT have to buy a uproc operated "sequencer" and really would
prefer some more basic approach. Transistors, and even some 555 timers or opamps
seem more robust to me. Don't mind building a circuit with relays...

Any ideas on how to make this go?
____________________________________________
check out these guys

https://www.downeastmicrowave.com/Default.asp

and look at this

http://01895fa.netsolhost.com/PDF/Manuals/TRS.pdf

    Mine sequences 4 channels (Relays) in just
under 1.5 secs.  you can adjust it.     It gets my
GasFet preamps out of the way on 144mhz.

/Dan
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WBear2GCR
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« Reply #9 on: November 30, 2019, 11:25:59 AM »



Yes!

Excellent! Exactly what the "doctor ordered"!

Took me a minute or two to see what the deal is.

It works as a comparator... the string of resistors connected to the inverting terminals
is a voltage divider. So, as the keying transistors supply voltage, they have to charge the
cap (C1) up. That's a ramp voltage. So as the voltage ramps, it corresponds to
the voltage at each sequential (-) terminal on each opamp, causing the opamp to kick
the relay. One at a time...

At first I was looking for individual R/C time constant networks!
Not finding them...

One could always use two opamps or more (as needed) at each position - corresponding
to time in the sequence. And, one can scale the resistors to move the timing between
relays (or use trimmers in there too...)

Personally, I'd use single or dual opamps, never quads.
Just my preference, in case of a failure, much easier to deal with - unless you happen
to have a drawer full of quads.

Yep, I like it! Cheesy

Thanks, Dan.

            _-_-bear
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N8ETQ
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« Reply #10 on: November 30, 2019, 05:46:31 PM »

One could always use two opamps or more (as needed) at each position - corresponding
to time in the sequence. And, one can scale the resistors to move the timing between
relays (or use trimmers in there too...)


     Or, as I did just pad in a Cap..

It's very versatile and configurable.  Mine has been online for
at least a decade.

/Dan
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