With C1 installed, the 436 has excellent performance on UHF analog and digital.
I recently took advantage of the $325 Amazon pricing and purchased a BCD436HP.
I updated the firmware and database, have loaded a Favorites List with some of my local channels.
At this point I am terribly underwhelmed by the reception performance of the 436. My local police and fire reception is perhaps 40% of the quality of the 396. It is static filled and hard to listen to. There is an occasional clear comm on some freqs, but they are few and far between.
I have verified the frequencies and settings are identical for both scanners, and that attenuator is off on both (that was my first thoguht).
I have also tried swapping the antenna's between the two radios (which seem to be the same antenna) with no change in performance.
I am suspecting a loose or bad connection between the antenna and the board.
Any thoughts if I am missing something or if I need to send it to Uniden for a service?
Thanks in advance for your input, insight and advice.
I have had the opportunity to test numerous 436 scanners against other Uniden models while doing internal GPS mods, and my testing indicates that when working properly, the 436 will match or beat the RF performance of mobile models.
Using separate antennas is never a valid methodology. Even if the antennas are exactly the same, the path from transmitter to receiver never will be. Use a single antenna and a splitter for a valid test, and of course make sure attenuation is off.
It is possible your 436 is missing C1 and is emitting mostly-UHF ststic from the battery compartment. This can interfere with reception when using the stock antenna, but has no effect when using an external antenna connected with a length of coax, and minimal effect when using an antenna like the Diamond RH77CA connected via the factory SMA-to-BNC adapter (using the adapter gets the antenna far enough from the noise that it doesn't interfere). Tune a SDR or another radio to an unused freq in the 400MHz range, set modulation to AM, turn the squelch all the way down, and put the antenna by the 436 battery compartment. If C1 is missing, vou will see or hear a significant increase in noise--a SDR will show about 15dB increase in the noise floor when the antenna is within a few inches of the battery compartment.
When I install an internal GPS, I install C1 if it is missing, and the UHF static from the battery compartment goes away. C1 has been missing in about 50% of the scanners I've modded--Uniden made some changes and newer boards have it and older ones do not.
Do a comparison with both scanners connected to the same external antenna with a splitter. If the 436 still has trouble, it may be defective. If that fixes the disparity in RF performance, then your 436 may be missing C1, and using any antenna other than the factory ducky (particularly ones with BNC connectors like the Diamond RH77CA) will make the disparity go away.
Newer scanners have it installed at the factory. Scanners 1-2 years old may or may not have it. Scanners more than 2 years old generally don't.
If your scanner doesn't have it installed at the factory, I do it for an additional $5 when I install an internal GPS, unless you have an older scanner (2+ years) that doesn't have the soldering pads for it.
From what I'm understanding, from having read many threads about 436HP reception, this radio was designed for the future, digital. I did not see whether you indicated whether your bad reception was digital or analog.
The digit after the Z indicates the year of manufacture. If it's a 7, that indicates a 2017 vintage and it will likely have C1 installed If it's a 6 or a 5, maybe, maybe not. If it's a 4 or lower, not likely. I log the serial numbers of the scanners I mod, and track whether they need C1 installed or not. As I get more data, I can be more specific.
.01 microfarad is what I've been using, and it has worked on every scanner I've modded so far.
Sending in your 436 for the clock repair makes sense. But if the antenna connector is loose, you can tighten it yourself if you can find a pair of needlenose pliers or a spanner with tips that fit in the slots in the metal ring around the SMA connector. It's actually a special nut that holds the connector in place.
Take the antenna off and look at the metal ring around the sma connector. It is a nut that you turn by engaging the slots in the top surface with a tool.