[Moon-net] 13 cm system question.

[peter blair]

Hi Trevor, Sorry to hear about the blown preamps. I dont have experience at 
microwaves of the Transco Y relay you mention but I offer the following 
comments.  I suspect that unless they are SPECIFICALLY  designed for 
microwave operation type N relays will have poor isolation as this will be 
determined only by the residual capacitance between the off contact and the 
common movable blade.  I checked one N type that I have, which IS designed 
for microwaves, and the isolation is >60dB. Most microwave relays I come 
accross are SMA relays which use much smaller diameter contacts and have 
smaller "exposed" areas and in some the off contact is grounded as well. I 
just did a quick measurement of isolation on one of the SMA types that I use 
and the isolation is also >60dB.
 I know this  may not be of much help at this point but I try to keep all 
the receive side on 23cm and above in SMA from the feed probe to the preamp 
input. The SMA connector design has lower loss than the N ( in my 
experience) and the smaller size reduces discontinuities and in fact allows 
you to terminate cables into preamps without connectors to get the ultimate 
in low loss.
 I suggest that  the solution is probably to find an SMA relay, they turn up 
here in our table top sales for about £20-30. Typical manufacturers are 
Teledyne and Radiall.You can use either a simple change over type or a 
transfer type, many of the ones that turn up these days are latching types 
but they are easily dealt with by adding another dc relay.Maybe look on 
e-bay?
 Seasons greetings, Peter G3LTF

----- Original Message ----- 
From: "Trevor Benton" <tbenton at bigpond.net.au>
To: <moon-net at list-serv.davidv.net>
Sent: Wednesday, December 26, 2007 8:58 AM
Subject: [Moon-net] 13 cm system question.


> Hello all & I hope everyone is having a good xmas.  I anticipated
> becoming operational on 13cm about now but have struck an
> unexpected snag in the form of two blown preamp devices in a
> short period of time which usually is due to either incorrect
> sequencing or insufficient isolation.
> The sequencing is ok & the same as I have used for other systems
> with never a damaged preamp.
> I measured the isolation between ports of my Super VE4MA feed
> with septum & found it to be 22 db.  Next I measured at 2301 MHz
> the isolation of the Transco Y relay [type 11300] & discovered it
> was only 18db.  My spare 11300 Transco is even worse at 15.5 db.
> With 40 db of isolation & 120w at the feed this means the ATF36077
> is seeing 12 mW at its gate with the spec sheet indicating the "absolute
> maximum" not to exceed 10dbm.
> I have been unable to get isolation fiqures for the Transco Y relay
> at 13cm though the info is out there somewhere however I would
> have thought it would be considerably better than 18db?
> In any event another SPDT relay with female N connectors is required
> before any progress is made & I welcome suggestions.
> Tnx for your time.
>
>  73`s, Trevor,  VK4AFL.
>
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