[NLRS] Typical SMA relay - Question

[John P. Toscano]

Mike King - KM0T wrote:
> 
> Hi all, working on getting back on 902.  Am looking at a SMA relay
> for TX/RX from the amp.  (I think my N type relay did not have enough
> isolation and fried the front end of the RX.)  Anyway, Isolation at
> 900 mhz for the typical transco SMA relay is way up there, 80 db+
> according to the dowkey catalog, but I cant find any power handling
> data on those relays.
> 
> Anybody have any data on power handling at 900 Mhz for them?


Hi, Mike.
Sorry, I can't answer that question.  But here is a relay you might
to consider if you still have room for a bigger one with N
connectors:

  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. . .

By the way, the above message will need to be viewed with a
FIXED-WIDTH FONT to make any sense.

73 de KB0ZEV