Most relays are not constructed of materials suitable for RF. Plastic rather
than ceramic is an example. They use a leaf spring material that can handle
current just fine at 60HZ or DC but it has a higher resistance than copper. And
since the current doesn't flow thru the entire cross section, only on the few
microns of skin depth the RF resistance is much higher. To get the gap needed
you would need open frame relays, which take up a lot of space. I have had one
surplus relay bandswitched amplifier which used the open frame relays that used
to be used as ladder line antennas switching relays. But it was a very large
box with a pair of 813s in it.
73
Bill wa4lav
________________________________________
From: Amps [amps-bounces@contesting.com] on behalf of Al Kozakiewicz
[akozak@hourglass.com]
Sent: Sunday, January 19, 2014 10:43 AM
To: MU 4CX250B
Cc: amps@contesting.com
Subject: Re: [Amps] Building an Amp 101
To make it clear, I've never tried this so I'm not speaking from personal
experience.
But it seems logical to me that if a vacuum relay is required for the voltages
and duty involved, then a bandswitch is out of the question as well, isn't it?
My thought is that, putting aside questions around stray-L that might arise
from the insertion of a relay, it's easier to find a relay with sufficient
contact spacing than it is to find a bandswitch with a large enough diameter to
maintain the same spacing between contact elements.
I guess these sorts of problems is why it's called engineering and not science!
Al
AB2ZY
-----Original Message-----
From: MU 4CX250B [mailto:4cx250b@miamioh.edu]
Sent: Sunday, January 19, 2014 9:32 AM
To: Al Kozakiewicz
Cc: amps@contesting.com
Subject: Re: [Amps] Building an Amp 101
Relays are certainly a possibility, Al, but for a nine band amplifier things
get a bit complicated. My latest project ( 90% completed) is a duo - band
80m/160m amplifier with a pi- L tank circuit, and for that I am using two DPDT
vacuum relays, each of which cost over $100.
Scaling that up to a nine band amplifier doesn't seem very practical or
cost-effective.
73,
Jim w8zr
Sent from my iPhone
> On Jan 18, 2014, at 8:52 AM, Al Kozakiewicz <akozak@hourglass.com> wrote:
>
> Why not use relays appropriate for the switching duty? Then the bandswitch
> can be just about anything or even remotely controlled. Plus you can locate
> the switch where it's convenient to operate instead of being constrained by
> the necessity to place it close to the RF components.
>
> Al
> AB2ZY
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