[TowerTalk] Help need Vacuum Relay Isolation 1.8 to 30 MHz

[Jim Lux]

What brand and model relay?
This is a spec that is usually given in the data sheet.
A typical value might be something like 40 or 50 dB isolation. (see, for
instance, http://www.mgs4u.com/relay.htm )
Or.. http://relays.tycoelectronics.com/datasheets/hc1_3_5.pdf
Gives a couple pF as the capacitance between contacts. At 30 MHz, that's
about 2-3Kohms.. into 50 ohms, that's about 34 dB...
Or.. http://www.jenningstech.com/pdf/coax/Coaxial.pdf
shows attenuations of 30dB for 300 MHz for the smaller ones.. The isolation
is probably in the 40-50 dB range for 30 MHz (factor of 10 frequency, factor
of 10 impedance, 20dB signal difference)

So.. 1500 W, less 40 dB isolation, is 0.15 Watts.  That's a pretty hefty
signal (+21 dBm) especially compared to the -100 dBm or less you're seeing
from the desired signals.

Do you have some additional isolation in the form of traps, etc.?

Granted, a "real relay" in a "real system" might work better.

The other technique is to run two relays in series.... some switching
topologies will do this naturally.



----- Original Message -----
From: "RCARIELLO" <RCARIELLO at si.rr.com>
To: "Towertalk" <Towertalk at contesting.com>
Sent: Tuesday, January 04, 2005 7:18 PM
Subject: [TowerTalk] Help need Vacuum Relay Isolation 1.8 to 30 MHz


> Vacuum relay RF isolation 1.8 to 30 MHz frequency range?
> I am planing to construct an antenna switch for a Multi-2 operation. Each
> antenna will be shared with two stations. Using two single pole normally
> open vacuum relays on series. The center connection going to the antenna.
> The open ends of each vacuum relay going to a station.
>
> At the 1500 watt power level will the single open vacuum relay provide
> enough isolation?
>
> How much isolation can I expect?
>
> Thanks for your help,
> Rich AA2MF
>
>