[TowerTalk] 4 square switching relays

[jimlux]

Pete Smith wrote:
> http://www.arraysolutions.com/Products/rf_relays.htm#top%20of%20page
> 
> You might have to ask, though, whether such relays are overkill.  For many 
> years TopTen has used $2 sealed relays in their antenna switches and A/B 
> boxes - there are quite a few of them out there in the contesting world.
> 
> 73, Pete N4ZR
> 
> At 07:53 PM 3/25/2009, W6SX wrote:
>> At 11:50 AM 25 03 2009, GALE STEWARD, K3ND wrote:
>>
>>> This link shows a pic of the Array Solutions 4-square box. It looks
>>> like they are using fairly large open-frames relays. Maybe this will
>>> give you some ideas.
>> Here's the link with the pictures.
>>
>> http://www.arraysolutions.com/Products/foursquare.htm
>>
>> Anyone have more details on the relays?
>>
>

It's not so much whether they are sealed or not, or even what the 
DC/60Hz ratings are.  You're using a relay that is designed for low 
frequencies for signals that are substantially different, so there's a 
fair amount of empirical cut and try.

I think what makers of such boxes do is buy a few relays, build some 
boxes, sell them, and see what the market tells them.  If the first few 
customers complain about the relays failing, they find another kind of 
relay, build new boxes, send em out, etc.  (or, the first boxes are 
being built for a buddy, or a semicustom sort of installation).

W8JI specified a particular design for the Ameritron RCS-8 switches, 
which MFJ gets custom.  He had reasons for his specs, but, on the other 
hand, I don't know that the reasons were based on analysis, or just 
experience with other relays.

Given the thin margins in the ham business, I doubt anyone has 100 
relays undergoing life tests.  The companies that DO extensive life 
testing charge accordingly (e.g. HP, Dowkey, Sector, etc)

Things you want to think about:

Capacitive coupling from RF path to coil/frame/across contacts.  It 
doesn't take much to make your isolation terrible. RF coupling into the 
coil can also lead to insulation failures.

Current handling and contact material.  An antenna relay has to handle 
both high powers (>10s of watts) and very low powers. This is unlike 
most power relays, which don't really care about microvolts or microamps.

There's a fair amount of discussion about particular relay types in the 
archives of the list, so some searching around would be useful.

Jim