[NLRS] Typical SMA relay - Question

[Chris Cox]

On Sat, 18 May 2002, John P. Toscano wrote:

>   http://www.tohtsu.com/products/czx-3500.htm
> 
> At 1000 MHz, the isolation is at least 65db and the power handling
> capacity is 800 watts.  Will that work for you?  (Insertion loss
> rated at 0.25 db.)  Downeast Microwave sells them for $105, as does
> RF Parts.
> 
> I suppose if 65 dB isn't enough, and you can stand the insertion
> loss, you could put 2 relays in series on the receive side:
> 
> 
>              |------ Transmitter
>              o
> Antenna ---o/
>              o
>              |       o----- 50 ohm dummy load (low power)
>              ------o/
>                      o----- Receiver
> 
>        CZX-3500    SMARLY
> 
> The leftmost relay would be the N relay with major power handling
> capacity, and any leakage through to the receive side of the
> N relay would be fed through the high-isolation SMA relay to a
> dummy load, which could probably be a BNC terminator resistor
> from a 10Base2 thin coax Ethernet network.
> 
> How much power do you run on 900 MHz?  500 watts at 65dB isolation
> is less than 0.2 milliwatts, or under 200 microwatts. . .
> 
Mike,

I don't think an SMA relay will handle the power, but John's suggestion is 
good.  Just one caveat; ensure that you don't dimply fix the SMARLY to the 
N relay.  You need to use either a 1/4 or 1/2 lambda coax section between 
them to get the true additional isolation.  The choice of 1/4 or 1/2 
depends on the specific relays as to whether they short the open contact 
to ground or leave it floating.  Specific details are in the RSGB (G3SEK) 
VHF/DX manual.

 -- 
73  Chris Cox  N0UK, G4JEC, ex-AB0CN, ex-G8PTC  RNARS #1157  EN34jv

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