Filtering for 23cm hilltop operation

[VK3JBL]

I'm just finishing up a W1GHZ 23cm rover transverter with the aim of backpack-able portable operation in vk3. I've built a 4 pole interdigital filter to kill the LO leakage and other spurious emissions after the PA (if 100-200mW can be considered power). What I'm not sure of is whether to put it inline with both RX and TX to protect the receiver from GSM base stations on 950. Is this required or recommended in vk3?

I've measured the insertion loss around 1.5db which is a bit high, but this is the first one I've built.

Touchwood I'll get my vk3 call in time for the winter field day, and get back on the air after 13 years.

Andrew

[VK3QI]

Andrew,

It would all depend on where you operate from and in the case of operation from a site that shares a Mobile Phone system, the relative separation distance, both horizontally and (especially) vertically.

I have operated from Mt Cowley in SW VK3 from the foot of the 200 foot Telstra tower and there was absolutely no indication of overload on 1296 from the Mobile Phone system (or any other service for that matter).

Other VK3's who have operated from other co-sited hilltops might have other experiences, but more it is more likely to occur on 2 and 70 where antennas are less directional.

Cheers

Peter VK3QI (VK3ER/p)

[VK3KH]

Andrew,
I agree with Peter. I have operated 23cm from many locations around Victoria, and have never had any problems with receive from any outside source.
If you are concerned, why not build a Minikits 23cm preamp to put in your transverter. This will give you more gain, and the design includes a filter that protects from everything below 1000MHz.
Look forward to working you on the winter FD.

Michael VK3KH

[VK3JBL]

Thanks for the replies. I'll leave the filter for TX only then.

I actually ordered the mini kits preamp earlier this week and it's in the mail. I'm just contemplating fitting it and a 1W mitsubishi module in the box.

Andrew