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[TowerTalk] Relay source wanted

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Subject: [TowerTalk] Relay source wanted
From: (Tom Rauch)
Date: Wed, 27 Jun 2001 00:32:32 -0400
> Just plain-Jane open frame, unsealed type - actually 5, 12 or 24 VDC coils
> are fine.
> -Mike

Did you say if transmitting, receiving, and how much voltage you 
might expect to have or the frequency range??

What works well for receiving are normal DPDT dip package relays, 
I have many dozens in use with some being used for at least 15 

Many control relays are suitable for transmitting applications, no 
need to buy anything exotic for HF applications using low or 
modest impedance lines. Loss in any relay will be immeasurable at 
HF, so the only real concern is the SWR bump they add and the 
voltage and current ratings.

I use Magnecraft W389CX-7 DPDT relays for most switching 
applications not handled by RCS-8V relay boxes or vacuum relays 
(where speed is required). 

That Magnecraft W389 relay is rated for 1HP 600VAC motor 
control applications. Since that relay easily handles 10kW into 
matched loads, it has a lot of headroom for SWR or operator 
errors... like hot switching at a kilowatt or two. I pay under $10 new 
for them, and they last forever. They not only reasonable in price, 
they have a plastic dust cover with mounting tabs.

If you want a single-pole double-throw relay, especially one for 
VHF, look at form-X contacts. This style contact pulls a shorting 
bar between stationary contacts, so they have the advantage of 
almost zero lead length through the relay. Since no thin long wires 
carry RF, they are generally usable to a few hundred MHz.

When picking a relay you want to look at physical spacing 
between contacts and the swinger's metal armature. Make sure the 
relay has thick (16 ga or larger) but very flexible leads, and wide 
contacts and contact support bars and terminals.
This is generally satisfied by relays used for motor control and 
ballast operation. You can bet if the insulation passes UL testing 
for 300-600VAC switching operation, and if contacts are rated at an 
AC switching current of 15 amperes or higher at any voltage (that 
rating is the actual hot-switching rating, which you will hopefully 
never do), the relay will be an excellent transmitting relay.


73, Tom W8JI 

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