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Relay and Two Bands

PostPosted: Tue Feb 09, 2010 8:02 pm
by DMOD
I can't recall exactly where (maybe Steve's multi-device trx?), but I saw that a relay was used to short a 15uH tuning coil so the 5uH coil (80 meters?) could be used.

If anyone has used this, was this relay anything special and did it cause any detuning or arcing problems?

I have the Digial VFO, the PDM generator board, and the PDM driver board completed for my ClassE trx.

Thanks

Phil - AC0OB

Re: Relay and Two Bands

PostPosted: Wed Feb 10, 2010 6:56 am
by KD3CN
Phil,
Check out the pictures on this page:

http://www.mouser.com/catalog/catalogUSD/641/1770.pdf

For this relay I started out with a SPST like figure 'A'. It smoked when rf arced down from the conductor on the top down into the coil. I changed it out and used a DPDT like the one pictured in figure 'B', and it works with no problem. I believe what I'm using is the Magnecraft 12VDC model W199X-12.

Looking forward to hearing the new e-rig on the air!

Karl

Re: Relay and Two Bands

PostPosted: Wed Feb 10, 2010 7:40 pm
by kf1z
I agree with Karl....

I use the Magnecraft relays with good results...

You want good wide contacts... and no part of the contacts or contact arms anywhere near a ground structure.

I was there to see Karl's relay smoke... it was nearly impressive...

The Magnecraft relays show up from time to time on ebay...
I usually buy up all the 12vdc coil units that show up :D

Normally less than $15... new price retail is around $30.

Re: Relay and Two Bands

PostPosted: Wed Feb 10, 2010 8:12 pm
by kf1z
On a recent build, I used a $4.00 relay from FairRadio.

It's a 30 amp contact, 12vdc coil.... SPST....

All it does is short the "160 meter" coil for 75 meter operation...

Works fine, no tuning or arcing problems...

Image

Re: Relay and Two Bands

PostPosted: Wed Feb 10, 2010 9:16 pm
by K6IC
Nice looking work Bruce !

That relay looks like a 'Double Make' which is probably the best form for this service. Two gaps when open, and a very short, wide RF capable (phosphor Bronze ?) shorting conductor, If my vision has not failed again.

73 Vic

Re: Relay and Two Bands

PostPosted: Wed Feb 10, 2010 9:46 pm
by kf1z
Those sketches in the PDF Karl linked to don't do those relays justice!

Here ya go...
OK FINE on the left...

DON"T use it on the right!!
(for high-current DC ok... but not RF!)

(I'm sure you know this Phil... but for the sake of others too...)


Image

Re: Relay and Two Bands

PostPosted: Wed Feb 10, 2010 9:48 pm
by kf1z
BTW

I usse the W199x-12 (on the left) for my TX/RX antenna relay.... no problems there either.

Re: Relay and Two Bands

PostPosted: Thu Feb 11, 2010 12:06 am
by DMOD
Thanks to all for the show and tell and the parts you used.

Phil - AC0OB

Re: Relay and Two Bands

PostPosted: Sun Feb 14, 2010 4:47 pm
by G1YLB
Hi

Sorry to hi-jact the thread, but what snubbers are you guys using on the relay coils, I just managed to pick up a couple of Mannecraft W199X-12. I'm just starting to put together Steve's PWM design :D

Thanks

Steve

Re: Relay and Two Bands

PostPosted: Mon Feb 15, 2010 9:14 am
by kf1z
Hi Steve,

I'm not using anything much at all... just a diode.

My large relays are all actuated by small relays, or switches.

The smaller relays have diodes across them, and are driven by a sequencer with stout transistors.

Re: Relay and Two Bands

PostPosted: Thu Feb 25, 2010 7:34 pm
by DMOD
Nice looking coils as well there Bruce.

What were the dimensions of the coil forms you used?

Thanks

Phil

Re: Relay and Two Bands

PostPosted: Fri Feb 26, 2010 6:10 pm
by kf1z
I'll have to measure the dimensions to be sure Phil...

BUT,

One was a can of green-beans...

The other, a propane torch cylinder.