BCD436HP Poor VHF performance

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Boatanchor

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BCD436HP Poor VHF performance?

OK guys, we need to nail this one down.

Either:

A/ The receiver really is deaf on VHF,
or
B/ The supplied antenna is useless on VHF (Appears not to be the case)
or
C/ The radio itself is generating noise which is then degrading reception on the stubby antenna.

So, in an effort to try and nail this down, we need someone to do a few basic tests on a BCD436HP.

Firstly, there must be someone out there who has access to a half decent signal generator to check the receive sensitivity.

My prediction is that the BCD436HP will produce the specified sensitivity figures when connected up to a calibrated signal generator..

However, now the tricky bit..

There is a distinct possibility that either CPU or DC-DC converter noise, generated inside the scanners plastic case, is being produced and radiated at such a level that it is then degrading receive performance on the VHF bands when the scanner is using a stubby antenna connected directly to it's SMA connector.
Such noise would be less evident, when doing bench testing using signal generators and shielded cables, since there is less opportunity for the noise to be induced into the front end.

Below is an internal shot of the BCD436HP daughter/RF board (courtesy of N9JIG).

The receive front end bandpass sections, one of which is covered in black goop) at the centre/top of this board. At the bottom of this same board is a NJM2360A based, DC-DC boost converter producing 20V. DC-DC converters such as these are typically used to generate the higher voltages required to run wide band VCO's and other tuning systems. Such converters are notoriously noisy due to their square wave switching that generates lots of harmonics and noise. This particular DC-DC converter is not shielded at all. No shielding in this area does not necessarily mean that this converter is the source of any noise, but it certainly is a prime suspect.

There is one very simple test to see if in fact the BCD436HP is 'noisy'.

A VHF stubby antenna, connected via a short length of coax, to a sensitive spectrum analyser (one that has a low noise floor and can see noise/signals at less than -90dBm) placed against the BCD436HP case may see broadband noise and possibly local oscillator and frequency reference carriers.

Another option would be to use the same antenna arrangement connected to a good quality SDR receiver such as a FunCubeDongle. If the BCD436HP is generating noise on VHF, the noise should appear on the SDR receivers spectrum display/waterfall.

If broadband noise is present, it is likely to be at very low levels however, it doesn't take very much noise to degrade receive performance on a receiver when the antenna is only 3 inches away from the source.
 

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sibbley

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My 436 is pretty bad on VHF and UHF analog with a duck. I don't have any test equipment and decided not to spend any more money by taking the radio to a shop to have it tested. I have literally tried about 20 different types of duck with this radio. Even 3 specifically tuned to the UHF and VHF frequencies I mostly monitor.

With that said, I've had excellent luck using mobile and attic antennas with the 436. Like I said above, pretty bad with a duck. A duck like the RH77 helps a little, but not much.

I've tried using a counterpoise either attaching headphones or an actual wire cut to 18". Both help, but still not up to par with my 346 or 396 on the same frequencies. The 3 mobiles and the radio shack antenna I put up in the attic (I don't remember the model number, but it's a cheap one), work very well on VHF and UHF.

I've used the mobiles either while in the car or attached to a cake pan in the house (all 3 are magnetic). I get really good reception with each of those. But, who want's to carry around a mobile antenna.

I know this is not what you were looking for, but this is how I sort of solved my issues with reception.
 

jonwienke

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I don't have reception issues on VHF or UHF with a whip antenna or an external mobile/base antenna.
 

AA6IO

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I also don't have test equipment. But as you probably know from another thread, I recently bought the WS-1080 to compare it with the 436HP. Indeed on VHF and some UHF, the WS-1080 (rebranded PSR-800) is more sensitive. About on the same level as my 396XT. Both are more sensitive on VHF and some UHF than the 436HP. Even ran 1080 against 436HP on LAPD P25 at 484 and 506 Mhz. 1080 picked up channels more often. However, when it did pick up channels missed by 436HP, the P25 decode was not very good. P25 decode still best on 436HP vs. 1080 and 396XT. (All tests tonight with RS center load antenna indoors near a big window in our family room.)
The 436HP sensitivity thing is an issue. This is with my firmware reverted to 1.02.03. With 1.03, it was even worse.
Interestingly, on distant weather stations, 1080 was also more sensitive than 436HP. However, when I moved the 436HP away from my body, some VHF and weather stations seem to pick up to near same level as 1080. 436HP seems very finicky with regard to position, near body, away from body, direction, etc, whereas the 1080 and 396XT do not seem to be affected much by positioning.
Maybe that suggests some clue about what is going on with 436HP.
Steve AA6IO
 

jonwienke

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I'm running firmware 1.0.3 (supposedly the worst for VHF reception) and I can pick up broadcasts from 6 of 7 weather channels with the 436HP when connected to my ST-2 base antenna. It's not mounted outside, it's tied to the railing in my attic stairwell in a brick building with a corrugated metal sheet roof--far from an ideal location. I don't doubt that some 436's have reception issues, but it's certainly not something that affects EVERY unit.
 

AA6IO

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Oh by the way, as Sibbley stated, I also get pretty good VHF with 436 when outdoors, especially with the big cake pan and mag mount antenna that I also use in the car. Once you get that signal at a certain level, the 436HP does real well. In Los Angeles, that is not really a major issue. But for more distant analog VHF, the other two scanners above beat the 436HP in a marginal situation (eg, RS center coil or my RH77 antennas when indoors). For P25, when the signals are reasonably good, you cannot beat the 436HP for decode quality in my opinion.
Steve AA6IO
 

sibbley

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I'm running firmware 1.0.3 (supposedly the worst for VHF reception) and I can pick up broadcasts from 6 of 7 weather channels with the 436HP when connected to my ST-2 base antenna. It's not mounted outside, it's tied to the railing in my attic stairwell in a brick building with a corrugated metal sheet roof--far from an ideal location. I don't doubt that some 436's have reception issues, but it's certainly not something that affects EVERY unit.
I would tend to agree with you. It's probably not every unit. I think it depends on the area in which the radio is used. When on the road away from my "home" area, the 436 performs pretty well across the spectrum. Not perfect, but much better than at home.

I only get 1 weather channel at home. I can get that with a duck, and of course the mobiles or attic antenna. With a duck, usually 4-5 bars and just a hint of noise. It's the lower powered VHF that is a huge issue for me.
 
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