Where to Find Wire and Cable + T/R Switch Question

[W1UJR]

For the 30K-1 project I need the following wires and cables, something my local electircal jobber is clueless on.
Suggestions?

1) The silver plated wire used for interconnects on the RF deck, round in crosssection, you see this same type and diameter on a number of old boatanchor items, Johnson Matchboxes, transmitters, etc. I need about 10 feet for RF innerconnects on the 30K output network.

2) 5 wire control cable, rubber insulation, stranded, needs to carry 120VAC. Rotor cable is too light, something like 14-2 but with at least 5 wires inside and a flexiable rubber jacket. I need 25 feet of this.

Tech question, aside from a Dow-Key, what do you guys favor for robust T/R switching?
Thinking of something which I can wall mount and use with either coax or balance feedline.

73 - Bruce W1UJR

[WBear2GCR]

Dunno where to get silver plated solid wire.
But you can take a bit of copper wire , coil it up, bring it to an electroplater and have them dip it in the tank for a few seconds... a minute would be more than enough to put a silver flash on the outside. Longer and you get a nice plating... if ur in Mass there are still electroplaters there, especially in Westfield and Springfield area...

A commercial electrical supply will probably have the requisite "control cable"...

For T/R I really like the electronic (tube) T/R switch that was made by Dow Key.
I have one.
It works ok fine!
The schematic is on BAMA, and also in the older Orr books in a similar version.
Wierd looking schematic, but the principle is this:
the transmitter is always connected directly to the ant, the receiver is connected through two stages of tube, the tube acts as a preamp when there is no RF present on the input end (where the xmitr and ant are connected) when RF comes down the pike, it biasses the two sections of tube OFF heavy, keeping dangerous RF away from the receiver. For mute you need another means. It will pin the S meter if you don't mute, but it won't blow the input coil on a tube receiver or the input xistr in a solid state rig (afaik).
The advantage of it is you can run break-in as fast as ur receiver can recover, and there is no pesky contact to key before the RF comes down the pike, and no arc potential on key-off of the xmitter...

Then you could update the idea and add in PIN diodes... not sure but they may have PIN diodes that will handle the full bore legal limit these days...

     _-_-WBear2GCR

[WA1GFZ]

Gee Bruce,
I saw a nice coax relay at Hostraders looked like a dow key. I think Dave Sneider had one on his table. looked new. Check Granger or Newark for multi conductor.

[k4kyv]

For T/R relay, I use a heavy duty open frame DPDT relay built in the late 30's just for the purpose.  Picked it up n.o.s. at a hamfest years ago.  It has a contactor type 110 v.a.c. coil - the core is like the E-laminations of a transformer, and the plunger is like the I-laminations.  The contacts are mounted on HD ceramic bars; the spacing between open contacts is more than 3/4".  The contacts themselves are almost 1/2" in diameter.

The relay was designed to directly switch open wire feeders.  But I use mine between the transmitter and the tuner, so I use only one pole of the relay.

The contacts are connected to the relay terminals with flexible stranded copper wire.  That was the weak spot.  After I had used it a  couple of months, that stranded copper wire broke due to metal fatigue,  from being flexed every time the relay was engaged/disengaged.  But I happened to have on hand a few feet of pure copper wire rope.  Have no idea what it was originally designed to be used for, but I unwound a short length of one bundle of strands, which looks to be the equivalent of #12 or 14 wire, and used that to replace the original stranded wire.  The wire rope strands are much finer in gauge and the bundle is much more flexible than the original used with the relay.  I have now used that relay for about 3 years with no further wire failure.  If it does eventually fail, I probably have enough replacement stock in that wire rope to last several centuries.

The wire lead to the unused contact is long gone too, but I  haven't replaced it.  No need to unless I decide to use both poles of the relay someday.

I used to use a dow-key, but my BC1-T turned the whole thing into a solid block of charcoal.  That's when I decided to change to the open relay.  Plus there is enough spacing of the contacts that there is little danger of a flashover during TX that would fry the front end of the RX.

One problem with the big relay is that it is noisy.  It engages with a loud "klunk" and sometimes the a.c. coil buzzes.  So I  mounted the whole thing inside a wooden box, where it is suspended with springs removed from one of those el-cheapo spring loaded movable-arm lamp holders.  I use 8 springs in all, arranged in the same fashion as the old fashioned shock-mounted double button carbon microphones that were suspended in a ring with springs.  The wooden box has a door with hinges and latch, resembling a small medicine cabinet (something else I picked up years ago at a flea market and kept around, doubtful that I would ever have a use for).

When the door is closed, noise from the relay is barely perceptible.

[Jim, W5JO]

Bruce the silver wire is called Buss Wire and can be found here:

http://coaxman.com/listitems.php?list=magnetwire&pagenumber=1

There are three pages so look through them.  Prices are reasonable and he will ship. 

73  Jim
W5JO

[WA1GFZ]

Bruce,
Fair Radio also has a nice coax relay on their features page. It looks new with UHF connectors.

[W1UJR]

Bruce,
Fair Radio also has a nice coax relay on their features page. It looks new with UHF connectors.

Thanks guys, very helpful indeed!

I could not find the silver plated wire on the Wireman site, perhaps you can zero me in on it.

Frank - I'm looking for a nice heavy duty relay to use for T/R switching on the 30K, something like the old KW Matchboxes used. I seem to have an issue using unbalanced feed, gets RF into the audio.

-Bruce

[Jim, W5JO]

Well the buss wire isn't on the site.  Just call or email him.  I know he has it, I bought a large spool from him at a hamfest in July.

wire@coaxman.com

866-745-9473

[Todd, KA1KAQ]

Bruce, why don't you drive down this weekend and raid the parts boxes in the cellar? I have a large box full of open frame relays, all shapes and sizes. Should be something in there that works, maybe even an old Leach or Potter/Brumfield keeping with the age of your rig. If you time it right, you can see the RayKit RA-1000 leave.

Come on DOWWWN!

[WA1GFZ]

Sorry Bruce I forgot you need 2 poles.