Tuning a UHF Bandpass Filter - RX Preselectors and What They Do

Another "short" video explaining my procedure for tuning RX cavity filters - in this case, a classic Motorla CLE1170A RX preselector commonly used in MTR, Quantar, and GTR repeaters.
Intro music: Funk Inc - Kool is Back (1971)
W9CR Wiki: wiki.w9cr.net
IMSAIGuy: ‪@IMSAIGuy‬

[@IMSAIGuy]

Thanks for the shout-out

[@W9CR]

One of the main reasons for the filter before the first RF amp in the receiver is that the first RF amp generally has a 100+ MHz of amplification. The RF amp has a max total output power, and strong signals will "rob" power from the intended signal, and can cause a weak signal to be covered up due to compression of the dynamic range of the RF amp.

[@ScottEvans-vk7hse]

Yes need to tweak my pre-selector on my Quantar... Seeing this has reminded me!

[@W9CR]

Tuning the filter off center is a great way to do this. I've done it several times, and while not ideal for insertion loss/s11, it's about balancing the system. Putting a notch on the transmitters for the receiver frequencies is still something to consider, as all solid state amps will make broadband noise.
Fuck those Mini-UHF connectors. The QMA is worse for vibration (mobile) use.
I just use a standard screwdriver, the tuning slug is at ground. One of the better ways to tune a many pole filter is in the time domain, if your VNA has transform on it. Not needed with this small filter, but with a 8 pole filter, or some of the 900 MHz stuff, it's needed. On the VHF Range 2 (150-174 MHz), I set the center for 146 MHz and as that's 5 poles, it makes it much easier to tune the range 2 down to cover the ham band. It's about the only way to tune it decently.

[@zapityzapzap]

I know what your project is...maybe because I believe you have discussed it on another site but still. I've always tuned these things according to the Quantar Site Manual. Seems to work pretty well. Only catch 22 is I use the tracking generator instead of the method using the signal level and frequency generator. I have so many of those probes laying around from all the Quantars.

[@dwgelle]

Very good! Keep em coming!

[@jeffnewport8287]

good info! KD9YTP