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Design >> RF Design >> Receiver protection circuitry options
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Message started by megabodger on Mar 5^th, 2008, 4:01am

Title: Receiver protection circuitry options
Post by megabodger on Mar 5^th, 2008, 4:01am

Hi,
I'm looking at the possibility of putting the Rockwell Collins Civil Aviation TCAS system on to UK Tornado GR4 strike aircraft. The major problem that I have is interoperability with other systems - in particular coupling between close sited L band antennas. Coupling levels of up to +34.5 dBm are predicted into receivers that are only good for +15 and +20dBm.
I cannot modify the bits of kit themselves to beef up the receivers and can only put something in line with the antenna feeds. Moving the antennas further apart is not an option either.......................

All the bits of kit supply suppression pulses, so what I'm looking at are simple shunt (or possibly series-shunt) PIN switches to short the antenna(s) down to earth whilst the other unit(s) is transmitting...........

Worst case is the IFF tx, which, when talking to Civil aircraft, is +59dBm with a duty cycle of about 1%, giving +39dBm into the TCAS antenna (TCAS rx is good for +35dBm) about 250mm away. Spot Frequencies are the Civil IFF freqs of 1030 and 1090MHz. Switch off-to-on and vice versa is needed in under 100nS to meet a 4MHz data rate - and I don't need to listen between pulses

Now, I'm a Systems Engineer, not a professional RF engineer but I've tinkered with RF and Military radar for about 30 years including home RF design up to 440MHz. What I'm proposing seems to me to be useable. An alternative proposed to me by a potential equipment supplier - phase/amplitude cancellation, also looks promising.

Any comments/suggestions before I go and talk in depth with potential manufacturers/suppliers?

Regards
Steve