HP-2: Home Patrol 2 VHF Hi reception noise

[Hdc30474]

I discovered something interesting today with the HP2. I was being frustrated by noise on VHF Hi and it killing NOAA weather broadcasts.

Of course I have tried other aftermarket antennas. Sitting on a NOAA weather channel, I noticed when I changed the volume, most of the noise went away. The noise was much less when the volume slider was displayed and not the entire display. Dimming the display does not help, so it isnt the backlight.

The antenna was picking up noise from the display. Extending the antenna a few inches above the scanner using a series of SMA adapters cleared up a lot of the noise. So, next will will fabricate a base for the antenna to attach to with a short length if RG-174 connected to the scanner.

If you are having the same trouble with noisy reception, maybe this bit of info will help. I first noticed far better reception using it mobile with a fender mount antenna. There is a bit of negative gain in that antenna system.

I also just now discovered I can now receive an adjacent county 800 MHz system I could not before. I could receive it well with the SDS100 and BCD325P2. So it isnt just VHF.

 

[dmfalk]

Sounds like the antenna is the culprit. What antenna have you been using, with your HP-2?

 

[KevinC]

Sounds like the antenna is the culprit. What antenna have you been using, with your HP-2?

Interesting. A passive antenna causing noise.

 

[dmfalk]

Interesting. A passive antenna causing noise.

More like RFI from the receiver coming through the antenna, like feedback. (Not properly grounded.) If using a different antenna doesn't change the situation, then there might be an internal problem, something inside not properly grounded and leaking RFI.

 

[Hdc30474]

Sounds like the antenna is the culprit. What antenna have you been using, with your HP-2?

As mentioned, other antennas were tried. Anytime they are connected next to the scanner. I had one antenna on a short cable and placed it near the displand and it wiped out everything. With the antenna connected as usual, I place a piece of aluminum foil over the display and it greatly reduced the noise. Stock antenna, antenna from BCD325P2, Remtronics 800 MHz which usually does well on VHF on other scanners, telescopic antenna.

The display is emitting the RFI. Try your scanner in front of your computer or laptop display. You will get the same thing. I will try the BCD325P2 with stock antenna that never has an issue next to the HP2 display.

 

[Hdc30474]

Interesting. A passive antenna causing noise.

Passive antenna is not of course generating noise. It is receiving noise.

 

[dmfalk]

I initially suspected the antenna as the culprit, since it would be easy to have a broken ground connection at the antenna. It is a grounding issue, and it might be a broken lead to the shielding, somewhere in the scanner. (I have an HP-2. I haven't had this problem.) You might need to send it to Uniden for a repair. Might. *shrug* You shouldn't be experiencing this kind of RFI leak.

 

[Hdc30474]

It appears to be the display is simply emitting RFI. When placing the antenna of the BCD325P2 near the display of the HP2, the NOAA channel goes from clear to very noisy.

 

[Hdc30474]

I initially suspected the antenna as the culprit, since it would be easy to have a broken ground connection at the antenna. It is a grounding issue, and it might be a broken lead to the shielding, somewhere in the scanner. (I have an HP-2. I haven't had this problem.) You might need to send it to Uniden for a repair. Might. *shrug* You shouldn't be experiencing this kind of RFI leak.

Do you have another scanner you can check for noise as I did with a BCD325P2? This may be a diificult one to explain to Uniden service. I bought it Aug 3 2024, so it is still under warranty. Thanks.

 

[Ubbe]

The display is emitting the RFI.

It's probably not the display in itself but RF leaking through the display as the rest of the scanner are shielded but the display are like an open hole where RF from the internal electronics are leaking out. It was something similar with the BCD436 but there the RF leaked out from its battery compartment and the BCD436 lost reception when used with its own antenna. Uniden never acknowledged that as a problem and when they test a scanner they use a coax cable connected to the scanner and to their communication analyzer. So if you send it in for repair it might come back with a note saying its working to its specifications.

/Ubbe

 

[Hdc30474]

It's probably not the display in itself but RF leaking through the display as the rest of the scanner are shielded but the display are like an open hole where RF from the internal electronics are leaking out. It was something similar with the BCD436 but there the RF leaked out from its battery compartment and the BCD436 lost reception when used with its own antenna. Uniden never acknowledged that as a problem and when they test a scanner they use a coax cable connected to the scanner and to their communication analyzer. So if you send it in for repair it might come back with a note saying its working to its specifications.

/Ubbe

I figured that is what would happen if I sent it in. The RF noise is similar to what I have always witnessed coming from computer displays. They emit a lot of RFI. I can have a handheld airband transceiver next to my laptop, and as soon as the laptop lid is closed, the RFI disappears. AM reception gets a lot of interference from computer displays. When I worked in Air Field Systems maintenance, I could come into the office with my handheld airband transceiver and it would break squelch and go nuts as I walked near any flat panel display. I am very interested to know if anyone else can test placing the antenna of a nother handheld scanner tuned to a NOAA weather broadcast near the HP2 display.

 

[Ubbe]

I am very interested to know if anyone else can test placing the antenna of a nother handheld scanner tuned to a NOAA weather broadcast near the HP2 display.

I did that to my HP-1 and couldn't detect any RF from it but huge amount of RFI at a lot of 162MHz frequencies from other gears, like computer screens and Sat/TV boxes. I only use external antennas and best possible shielded coax from each scanner as I know I have all these RFI sources. If a SMA connector unscrews a couple of turns I instantly suffer from these RFI sources when its ground no longer are perfect.

/Ubbe

 

[Hdc30474]

I did that to my HP-1 and couldn't detect any RF from it but huge amount of RFI at a lot of 162MHz frequencies from other gears, like computer screens and Sat/TV boxes. I only use external antennas and best possible shielded coax from each scanner as I know I have all these RFI sources. If a SMA connector unscrews a couple of turns I instantly suffer from these RFI sources when its ground no longer are perfect.

/Ubbe

Thanks! I am not sure if the HP1 is comparable to the HP2 in design or construction. I do use the HP2 mobile for a statewide 700/800 Mhz P25 system with 245 sites. I use a GPS receiver with it mobile. It works just fine in that setup, and works well connected to an external antenna with an antenna amplifier that compensates for feedline loss. But, using a side connected antenna it gets RFI from that display. My BCD325P2 gets the same type of interference if the antenna is within about 2 inches or 5 cm of the SDS100 display. It can be about twice that distance from the HP2 display and get about the same level of RFI.

 

[Ubbe]

I did try my SDS100 as well, and also other scanner displays but none radiated anything that could be detected by me when sniffing around with a BC346XT with its squelch open and tuning in 12,5KHz steps while having computers and media boxes turned off. I can then only hear if there are some carriers, modulated with data or silent, that interfere.

I probably need to receive some constant signal with the 346 and check if it looses reception when its antenna are close to a display. I can set a signal generator to full power with an antenna on it at a frequency but it seems its also interfering with 800MHz frequencies, so it's on every frequency that the display on a HP-2 and SDS100 generates noise that blocks out reception?

/Ubbe

 

[Hdc30474]

I did try my SDS100 as well, and also other scanner displays but none radiated anything that could be detected by me when sniffing around with a BC346XT with its squelch open and tuning in 12,5KHz steps while having computers and media boxes turned off. I can then only hear if there are some carriers, modulated with data or silent, that interfere.

I probably need to receive some constant signal with the 346 and check if it looses reception when its antenna are close to a display. I can set a signal generator to full power with an antenna on it at a frequency but it seems its also interfering with 800MHz frequencies, so it's on every frequency that the display on a HP-2 and SDS100 generates noise that blocks out reception?

/Ubbe

I first was aware there was a reception problem when the HP2 could barely receive NOAA weather broadcasts on 162.4 and 162.525 MHz that the BCD325P2 was receiving full quieting. Of course I tried them side by side using the same type antenna and changing position and location.

I am using the same Uniden BNC rubber duck antenna on the HP2 and BCD325P2. I have a few of these. That antenna works far better than the stock HP2 antenna. For a broadband handheld antenna, I think they are under appreciated. I am refering to the BNC rubber duck antenna that comes with the BCD325P2.

What clued me in on the HP 2 display was when I adjusted volume on the HP2, and then when the display was reduced to showing the volume slider instead of all the usual things normally on the display, the reception on the HP2 cleared up. So I focused on the display as being the noise source. By using a series of SMA barrel connectors stacked, I moved the antenna a few inches above the HP2 and farther away from the display and the reception of 162.4 and 162.525 weather broadcasts cleared up.

While receiving 162.4 and 162.525 with the BCD325P2 and placing its rubber duck antenna within 5 cm of the HP2 display, the reception gets very noisy. This also occurs placing it in front of the SDS100 display, but closer at half the distance.

Using a short SMA patch cable and BNC adapater to connect the BNC rubber duck antenna to the HP2, and placing the antenna about 10 cm in front of the HP2 display causes very high noise level in the reception of 162.4 and 162.525.

I have been unable to receive an adjacent county 800 MHz P25 trunked sytem on the HP2 that is clear on the BCD325P2 using those same antennas. When I extended the BNC rubber duck antenna connection of the HP2 farther away from the HP2, I was able to receive it.

 

[Ubbe]

I have been unable to receive an adjacent county 800 MHz P25 trunked sytem on the HP2 that is clear on the BCD325P2 using those same antennas. When I extended the BNC rubber duck antenna connection of the HP2 farther away from the HP2, I was able to receive it.

Antennas work together with a groundplane, that usually will be the metal chassi of the scanner. Extending the antenna will detune it and work very differently compared to having it in its original position. So that can be an antenna issue.

When having the display interference issue, are the SDS100 and HP-2 run on battery without any cables connected to them or do they have USB or power supply cables attached to them? I will try and mimic your installation and test with a signal generator how much a display interfere with RF reception, if it might be some general RF "smog" type of noise covering all frequencies. Usually USB data cables emit a lot of RFI and the best type are those that have a ferrite core around them at its ends.

/Ubbe

 

[Hdc30474]

Antennas work together with a groundplane, that usually will be the metal chassi of the scanner. Extending the antenna will detune it and work very differently compared to having it in its original position. So that can be an antenna issue.

When having the display interference issue, are the SDS100 and HP-2 run on battery without any cables connected to them or do they have USB or power supply cables attached to them? I will try and mimic your installation and test with a signal generator how much a display interfere with RF reception, if it might be some general RF "smog" type of noise covering all frequencies. Usually USB data cables emit a lot of RFI and the best type are those that have a ferrite core around them at its ends.

/Ubbe

All battery. I should have mentioned that. However the USB cable I use with the HP2 when it is operated on external power, does have a ferrite core near the USB mini end.
Regardless of any antenna resonance change when connecting through a short patch cable, it is quite evident the display is emitting enough RFI to have a negative effect, and as long as the antenna is not near the HP2, reception is noticably improved. It also interferes with the BCD325P2 when it is placed near it. I cannot tell you the signal level that is actually getting to the antenna input of either scanner when receivng the weather broadcasts. However, even when the RFI is isolated, the BCD325P2 is still more sensitive than the HP2 receiving the weather broadcasts at 162 MHz and the adjacent county 800 MHz system.

I do not have a signal generator that I can use to measure sensitivity. I wish I still had access to the test equipment at the ATC squadron I retired from. For general testing, I use the uncalibrated output of an antenna analyzer. That antenna analyzer goes to 170 MHz, but the harmonics are still at a very useful level. My oscilloscope is limited to 100 MHz, so I have no way to accurately measure the output. A good used commercial grade signal generator is on my wish list, but it would get used so little I have not yet justified the expense.

One other thing mentioned earlier. With the antenna attached directly to the HP2, if I place a piece of aluminum foil over the display, the noise is greatly reduced, but not as much as getting the antenna farther away from the HP2.

It is a curiosity, and I appreciate your effort. My current opinion is that what I am experiencing is a design characteristic of the HP2, and not a defect with this particular unit.

 

[Hdc30474]

This just got a lot more interesting. I ordered a small mobile magnet antenna mount with a BNC base on Amazon with 15 foot RG-58 and BNC connector, to see how effective giving some additional distance between the antenna and the HP2 would affect reception. I intended to shorten the 15 foot cable, but I tried it with the 15 foot cable using the Uniden rubber duck antenna. Reception of weather broadcasts improved greatly and were almost as good as the BCD325P2 which has the same antenna connected directly.

Even with the antenna sitting on the magnetic base and right next to the antenna input, it still worked as well. However, if placed near the display it gets noisy again. The base was not sitting on anything metal. But when I moved it to a metal table, it improved. The additional cable is probably providing a counterpoise.


I expected the adjacent county 800 MHz to be worse with the 15 foot cable due to feed line loss, but it wasnt. When I shortened the cable to 3 feet, it did not change the performance on 162 MHz. It did slightly improve 800 MHz.

It seems maybe the case of the HP2 provides no counterpoise at all. I have not removed the cover to see if there is any metal frame at all, or is everything just mounted to plastic.

Connecting the antenna directly to the HP2 and attaching an 18 inch (7 cm) piece of wire for a counterpoise seems to help very little.

 

[Hdc30474]

Conclusion, the BCD325P2 is far less prone to nearby RFI and a bit more sensitive with the same remotely connected antenna. Wish I had a signal generator.

HP2 works great with an outside antenna or in the car on a mobile antenna. But on a directly connected antenna, it suffers.

This was first noticed when we rented a vacation house last Christmas. From that location, the HP2 could not pick up the nearest NC Viper site (not simulcast), or any NOAA weather channels. The SDS100 and BCD325P2 could. All radios using their supplied antennas.