The AM Forum

I recently read the post on Johnson T/R relays and discovered they didn't work well stock on 160. I may modify mine, but what would be better external relays to use?

Dow Key relays work well if they haven't been abused.

(http://www.wb2rcb.com/images/dow.jpg)

What was wrong with them on 160? I find with the type that Pete has posted, that often it's a good idea to pry off the end button and spray clearer in it,then manually work the relay so the contact will mate and then it will be good to go almost for an unlimited amount of service.

He's referring to the Johnson electronic T/R switch. Specs. are from 3.5 to 30 MHz.

This hot box:

(http://www.n4mw.com/trsw-1.jpg)

Oh, those, I read story's where they were a source of TVI back in the day?

The Johnson (and other electronic) TR switches are very useful if you are running full break-in CW but otherwise I prefer a mechanical relay.  The Dow Key style are convenient since the connectors are already in place but they don't always age that well and tend to be pricey.

For less than legal limit rigs I use regular cube type relays mounted in a box with appropriate connectors.  I think even your local Radio Shack store still carries suitable relays.  A 2 pole relay is sufficient, one pole to switch antennas and the other pole is wired for receiver muting.  For my Viking 1 and Viking 2 I use 4 pole relays and one additional pole is used to keep the external VFO keyed on CW since I don't operate full break-in and this gets rid of VFO chirps.

I use a vacuum relay with my Desk KW and Viking 500.

The EFJ relay (and others following old QST and handbook design) are clever but it is my understanding (i.e. I have read this and have not verified) that they are okay with tube receivers but may blow out solid state front ends because the tube in them that's exposed to the tx RF doesn't cut off instantly.   so supposedly you're okay with a rx like my 75A-3 that is rated for up to 50 v. RF on the ant. terminals but a modern little chippie silicon surface mount box would sizzle unless you operated QRPeeeee. 

The Dow Key with the sliding tit in the RX side has excellent isolation even on 10M but the earlier ones would often fry a tube receiver with high power, fine at 100W.

They are easy to repair and align and spare coils and external contacts are easy to find on a fried junker. Always have a DVM when at hamfests.

A problem using them is when a seperate TX/RX uses one with external contacts to feed into and control a commercial amp using the much faster open frame or vacuum relay. The TX is transmitting into an open circuit for a bit and some dont like that.

Proper sequencing can be a PITA at times as Ive found out on VHF/UHF with tower mounted preamps.  And never in the summer and usually in an ice storm :'(

With the other way around, a rice box on AM will often be hot switching most linears which results in arcing caps and bandswitches.....SB-220's in particular....that one nut case claims are parasitics ::)

Carl

    Not enough info in the OP. Power level would be
helpful. but never the less a Junkston TR Box ain't
the solution...

/Dan

Thanks for the info. Everything I own is tube type, and made in the USA before 1960. At present I am running barefoot rigs and will be switching the 100 watt transmitters eventually into my old home brew 4-1000a amp after I resurrect it from storage in my garage.
73,
Ed-kv5i
P.S.
The thread I was reading was concerned with 160 meter receive attenuation through the Johnson switch (I have two). I doubt I will get much, if any, DX  this time around, but I had over 50 countries before on cw, and if I can hear em', I want to do my best to work em'  ;)

I use mine on 80 meters and it works fine, I'll try it on 160 to see what happens.  Pete, you are right about hot box, I was alarmed how hot it got!  For QSK CW I use a vacuum relay, but have experimented successfully with PIN diodes.  Only problem is lightning taking out the diodes.

On 3.5 to 30 MHz the Johnson T/R switch has about 3 to 6 db of receive gain. On 160, it tends to act more like an attenuator. Strong local signals can still be heard but, for the most part at least with the two I have, receive sensitivity is greatly reduced. Most likely, some diddling with the T/R's receive output circuitry would be required to also cover 160 without signal reduction.

DowKey made an electronic TR switch as well.
I have grabbed the schematic online.

More compact slightly different circuit.

Today one *might* make a PIN diode bias switched TR.
Although I haven't seen one made commercially, which I wonder why.

The other thing one could do is to use something like a Tranzorb across the
receive line to clamp any over voltage on the input of a receiver. Maybe this
is a good general purpose idea. I have no idea if merely dropping such a device
there will somehow have a negative effect on distortion or something else. That would
be good information.

Actually, a series fuse (small) with a transzorb following would add a bunch of
overvoltage/current protection. The idea being if the tranzorb was hit hard enough to
clamp and long enough it would blow the fuse before the current limit of the Transzorb
was reached causing it to blow.

Random thought.

I'm happy with the Johnson T/R switch I borrowed. Have not used it on 160M or modded it.
I believe it is important for best gain if the TX plate circuit is on the same freq. as the desired RX frequency. The gain goes down if the TX is unplugged from it. -at least on the one here.

I still plan to use a mechanical relay at some point. The Johnson let me get the TX on the air right away.
It held up to a 700W carrier 100% modulated during tests with a dummy load.
No idea about TVI, thanks for that tip.

That's true with the transmitter tuning and both being on the same band. Actually, if you change bands, you can use the receiver (tune for maximum noise) by adjusting the plate and load caps of the transmitter to get them close to where they should be. No issues with TVI; would have to roll back the clock 50 years.

I use two of these for my T/R switch for my Valiant.  Just mount them in a metal box.  If you have 12V available from the rig, you can get 12V relays and use that instead of 120V.  If you only have 6V, then make a voltage doubler and then you have 12V.   Use the doubler I have attached so you don't have to float the ground

73 de AB3FL

I like the Dow Key transfer relay, I use that on 2M so I can easily run barefoot and switch between 100W/1500W or bypass the RFC brick and run 10W out of the transverter.

I smoked my Johnson T/R relay with the GPT-750 running into a resonant ant on 80m a few years ago.

I went back to using a good dow key relay for T/R, and no problems. You could use any suitable open frame or cube type relay with heavy enough contacts to do the job on HF as well. Use what you might have on hand.

Al VE3AJM

I have used Dowkeys on almost everything and still have alot of them running. They are GREAT, however, They dont make new ones and old ones are iffy at best.  Sometimes, You get a good one that some HAM has been inside trying to clean and fix.  Hams wont throw anything out, most are hoarders.  SO they will keep and later pass on a damaged or worn out dowkey.

I have an NC183D here that has no RX and that was likely because of a failed dowkey. keyed down on the valiant, the dowkey shot the Disk, spring and plunger out across the room in the middle of a QSO.  Later, I find out the rim of the solenoid can had marks all around it where someone pry'd it apart for repair or cleaning.

Many a receiever has been blown over a bad/failed dowkey relay.

If they made brand new 110 volt dowkeys I would buy them and be set. But they dont.

I have gone to the Cube relays with socket here for some rigs. They are cheap, Easy to wire up and seldom fail. If they do, Just unplug the relay, throw it out, and put a new relay in.  You can get relays that have lots of contacts for switching all kinds of things like muting the receiver, AM sync detector, ssb adapter, or speaker.

I have two Johnson TR switches here.  They run Very very hot,  One smoked all of the sudden on 160 meters. 

One I used behind the J500 and the first time I keyed, It sent a sample of the power to the receiver and blew my ESP preamp out. 

I put the Johnson TR switches back in the closet and just use the cube relays in a small project box with SO 239 panel connectors.

C

Back many threads ago, I mentioned that I always wire in a #47 lamp in series with the tube receiver antenna terminal and/or a pair of back to back diodes from the antenna terminal to ground. Saves destruction of whatever receiver antenna coil happen to be connected to the input antenna terminals.


DowKey stills makes RF switches/relays but they're not cheap and don't look like the traditional ones from the 50's and 60's.


Could it be because the Johnson T/R switch wasn't designed as manufactured to run on 160 meters. Their spec calls for 3.5 to 30 mc.

If you're into the tradional look of DowKey type relays, you might consider the Tohtsu Coaxial Relays:

(http://www.rfparts.com/coaxial/relays/cx600mb.jpg)

The complete list of them are here: http://www.rfparts.com/coaxial.html

Pete

Can you post up the link for the Dowkey 110 volt/so239 relay for us?   Also while you are at it, Can you post up the link for the RF parts listing for the 110 volt/so239 relay? 

Thanks

C

Why in the world would you use 110 volt AC coil on any relay when presently low voltage coils are readily available on relays that do the same thing?  I always side on safety and never on the "I am invincible" theory. All my old Dowkey relay 110 AC coils were thrown away years ago and replaced with 6 or 12 volt DC coils. The RF Parts CX-600M (UHF connectors) is a great Dowkey replacement for use on the HF bands and even up to the VHF region.

Ok.  I just wanted to show that they do in fact DO NOT make these dowkeys anymore. Hence the reason we have gone to reliable and cheap Cube relays.

Thanks Pete :)

C 8)

LOL
As I said in an earlier post: "DowKey stills makes RF switches/relays but they're not cheap and don't look like the traditional ones from the 50's and 60's." Live on  8)

Got the valiant and NC183D fixed after the dowkey stuck.  W0VMC needed some tubes so we did a swap for one of his Coaxial relay boxes.

Its very nice wrinkle black, has Normaly open and closed terminals and also has an rca/phono connector for accessories.  No idea what they cost. It works perfectly.  I threw the dowkey out.

In the past I just built my own Coax relay box with connectors.  But this worked out for me since I have had zero free time to work in my shop. 

Gonna be on 160 tonight with it :)  Maybe I can make some contacts.  Should be fun.

C

With the prospect of your 4 by 1, I recommend building a vacuum relay into a metal P-box punched to take your favorite bulkhead connectors and a grommet for 24V power into the relay.

Fair Radio Sales has good prices on Jennings (or equivalent) HV relays. Very fast acting, which addresses the problem of keying up without a load on relays with a slower changeover.  You can find them at hamfests too if you want to take a chance.

Here's the one I use --

https://www.fairradio.com/catalog.php?mode=viewitem&item=5308

Got a small, thick aluminum box with recessed lid and did it up.
I think I got the Hammond 1590 for the job, and got a set of Amphenol chassis mount RF connectors for common, tx and rx.

http://www.hammondmfg.com/dwg.htm

With good layout and your best soldering, there shouldn't be a significant loss through 10 meters.

I've used a E F Johnson electronic switch for several years with my NCL2000 and its never been a problem, and they are rated for 4KW PEP 80 thru 10 meters.    The box does in fact get pretty darn hot.

(http://i670.photobucket.com/albums/vv62/mikeinkcmo/Radios/E%20F%20Johnson/EFJohnsonTRSch.jpg)

I also use those die cast boxes, they are very nice.

Yes. They do work but not on 160.

C

If you aren't working QSK CW, the need for an electronic TR switch is about zero. For AM it would seem they would be more bother than they are worth.

Your suggesting to use a manual coax switch?

C

No, a relay vice an electronic TR switch. Then again, with some of the old buzzard transmissions, a manual switch probably wouldn't be much of an inconvenience for some.

Oh.  Yes. I agree Steve.  QSK would be the only real use I guess.

C

Unless you are Ralph, W3GL - the fastest PTT in the world!  ;D