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Uniden Advanced Technical Topics For all threads regarding technical performance of specific models or general higher tier, technically oriented discussion of the technology used in Uniden scanners. Please use the Tech Support forum for all normal questions.

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Old 07-03-2014, 2:57 AM
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Default BCD436HP vs BCD396XT Ear Phone helps reception

There are a couple of threads about reduced sensitivity of the 436HP vs 396HP at low VHF. I have been one of the posters. But I thought this deserves a new thread. Administrators: Move to correct place if necessary.

I had my headphones on this morning listening to 436HP in office. Usually I just listen with the speaker. For some reason, the 436HP seemed a bit more sensitive. OK, put it away, and brought it home for some testing this evening.
The gist of the other threads, been experiences by several people, is that since the update to ver 1.03.00 on 436HP, that sensitivity has dropped on VHF reception.
For the last couple of hours, I have again been comparing the 396XT vs 436HP on low VHF and weak weather channels about 80 to 100 miles away. As I reported previously, the 436HP does not hear as well as the 536HP. This is across the board with RS Coil antenna, Austin Condor, and Diamond RH77CA on both scanners for comparisons.
However, with each of the above antennas attached, when I put my headphones in jack of 436HP (good set of headphones I use for CW DX), any slight background noise on the 436HP seems to drop to nothing, and the sensitivity for the weak stations on VHF/Wx seems to be more in line with the 396XT. I had to do a couple of double takes, I repeated this with each antenna and the headphones (cord length about 4 feet) and each time the sensitivity on 436HP seems to pops up a few dB.
Trying the same thing with the 396XT, no difference with headphones in or out. Same good sensitivity.
But repeatedly, when could not hear distant Wx stations on 436HP without headphones, plug the headphones in, and signals pop up to about same level on 396XT.
Before someone says, well you hear better with the headphones, maybe true, but I have been around radio for 52 years, and I tell you, plugging the headphones drops any noise on the 436HP and seems to improve this lower sensitivity issue that we have discussed since ver 1.03.00
Can someone else with similar issue confirm this with a "plug in headphone (at least 3 or 4 foot cord) test." If this is true, wonder why it is so. But if it is true, it may also be good news.
Steve AA6IO
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Old 07-03-2014, 3:29 AM
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Without knowing the internal design of the 436 audio circuit(s) I am only guessing here; it might be that the headphone cord is providing an improved ground plane for the antenna.

You don't specify the frequency but mention "low VHF" which I take to mean 30MHz to 50MHz. That band is difficult to receive with handhelds and short portable antennas with limited ground planes. An antenna in that range needs to be several feet long for a quarter wave and the ground plane should be comparable to that. Of course that's nearly impossible for portables. But adding any extra length of wire to the ground plane of the radio will help.

Try the following:

Get a long length of wire (at least as long as your headphone cord) and strip off enough insulation at one end to wrap tightly around the ground of the antenna connector. Extend out the wire (with the antenna connected as best possible so that the radial wire can be accommodated) away from the radio at various angles and see how the reception changes relative to how it is with no radial. It should improve with the radial wire especially on low band.

Why is the 396 good without the headphones and has no noticeable difference when the headphones are plugged in versus what you experience with the 436 I don't know for sure. My guess is that the headphone circuit is slightly different and the radio may have more internal metal in the case or internal shielding which makes it appear as a better ground plane but I'm really grasping at straws here without more info.

-Mike
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Old 07-03-2014, 4:28 AM
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Mike,
Actually, these frequencies are high VHF around 155 Mhz with a lot of the older analogue stations still here in LA County. But what you say makes good sense, and I will give that a try in next day or two.
Regards
Steve AA6IO
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Old 07-03-2014, 7:05 AM
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Default Counterpoise

Here is a link for making a handheld counterpoise.

HT Antenna Modification - Get Better Performance From Your HT Antenna
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Old 07-03-2014, 7:13 AM
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Ki6asp
Thanks
AA6IO
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Old 07-03-2014, 1:44 PM
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Just preliminary testing, but using the mono earphone with the 436 does seem to help with reception. Using RH77 antenna. Will keep on checking at different locations and with other antennas. No change in reception using the 386xt with the same antenna. I'm on VHF High and UHF "T" band.

Great find!
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