BCD436HP/BCD536HP: Bcd436hp deaf inside city

[Ronnierozier2]

Central Mississippi in the Ms delta. Just picked up a bcd436hp. Have an issue I would like some insight on. I’m in the middle of town in Greenwood MS and cannot hear a thing on my local law enforcement MSWIN system is what they talk on. What’s odd is to hear any law enforcement I must drive a few miles outside the city in any direction to start hearing traffic. Once outside of town I get the DAT icon with some bars. At my home with a mag mount 35’ in the air on top of my roof I get nothing still. I’m on top of my roof at this very minute typing this post.

any ideas what’s going on? Howdo the police talk on their radios when I can’t even get a signal on my roof? I had a police friend of mine swing by and his portable has lots of traffic when my 436 has none. I have an sds100 on order that will be here Thursday.

any insight would be appreciated.

 

[StoliRaz]

Is it a simulcast system by any chance?

 

[Ronnierozier2]

Is it a simulcast system by any chance?

It’s not I’m about 75 miles north of the nearest simulcast site. I think it’s signal related cause I just went 4 blocks down the read and started hearing traffic. When at my house the DAT icon never shows up but 4 blocks away it starts to show up with bars in the top right corner then I hear traffic

 

[kb5udf]

I have a 436 and the portable SDS. Both of them get overloaded by cell towers with FirstNet. In your county you are trying to receive a control channel around 769.5mhz or so. A wall of strong signals may be <2mhz below that, in the form of first net, which is a cell/data type service, desensing your receiver. That's why it might be working better out of town, because of less sites.

Suggestion for at home. Put the factory antenna back on, and move around the house. You may find a few "magic spots" where reception is fine, sometimes an inch or so can make al the difference.

 

[Ronnierozier2]

I have a 436 and the portable SDS. Both of them get overloaded by cell towers with FirstNet. In your county you are trying to receive a control channel around 769.5mhz or so. A wall of strong signals may be <2mhz below that, in the form of first net, which is a cell/data type service, desensing your receiver. That's why it might be working better out of town, because of less sites.

Suggestion for at home. Put the factory antenna back on, and move around the house. You may find a few "magic spots" where reception is fine, sometimes an inch or so can make al the difference.

I’ll give that a try, im a little hesitant due to the fact I have a metal roof. I even went up on the roof today about 30’ with a mag mount and it was no better. But 1 block over at a friends house I was able to stand under his carport and get a pretty good signal. 3 bars on all my DAT channels.

 

[donc13]

I’ll give that a try, im a little hesitant due to the fact I have a metal roof. I even went up on the roof today about 30’ with a mag mount and it was no better. But 1 block over at a friends house I was able to stand under his carport and get a pretty good signal. 3 bars on all my DAT channels.

A mag-mount needs to be grounded to the same "ground plane" as the radio. In your case, the roof itself. The magnet only holds the antenna in place.

Not knowing if your roof is electrically connected to a 4' or longer ground rod literally into the ground around your home....I am not going to suggest a way to ground your antenna. Get a qualified and licensed electrician to insure both the cable ground lead and the roof are properly connected to the same electrical ground.

 

[mmckenna]

A mag-mount needs to be grounded to the same "ground plane" as the radio. In your case, the roof itself. The magnet only holds the antenna in place.

Not knowing if your roof is electrically connected to a 4' or longer ground rod literally into the ground around your home....I am not going to suggest a way to ground your antenna. Get a qualified and licensed electrician to insure both the cable ground lead and the roof are properly connected to the same electrical ground.

Not quite.

The magnetic mount antennas achieve their connection to the ground plane via capacitive coupling between the antenna base and the material it's sitting on. To RF, the small gap between the magnetic base and the roof (even if there's paint/powder coating) is virtually invisible to the radio. There's a very slight impact when comparing magnetic mount antennas to a permanent mount antenna, usually about 0.1dB of additional loss on the mag mount. 0.1dB isn't something that you'd hear with your ears, and it's not the cause of this problem. The issues with mag mounts usually arise when transmitting and there isn't a good DC ground. DC ground and RF grounds can be different things.

Grounding is good for lightning protection, and safety, that's why it's required by the NEC. For a temporary test installation like this, it's not going to make a difference.

I suspect the issue is the scanner front end getting swamped by a nearby 700MHz cell site. Grounding isn't going to fix that, and neither will installing a permanent antenna.

An RF filter that will have a sharp rolloff below the 700MHz LMR band would probably resolve the issue.
When you move away from your location, and proximity to the cell site, it's allowing your scanner to hear the system you want to listen to.
I've had this happen with other radios. I had an ADS-B receiver (1090MHz) completely swamped by a Verizon LTE site that we were sharing out tower with. I was able to fix it by moving the ADS-B receiver to one of my other sites.

 

[captainmax1]

I am temporarily living in a duplex community for a year or so. Since no masts are allowed, I have attached 3 mag mount antennas out a back window onto the steel roof for 144, 440 and 800MHz. I get great results with local repeaters 10 miles away on 144, 440 UHF/VHF/DMR and pretty good reception with repeaters 20 miles away on the mainland. The 800 MHz mag mount gives me full bars for my local P25. I have 8 scanners running through an 8 port Stridsberg multicoupler. I also get full bars when my BCT15X is on Marine and good results with Air, GMRS/FRS/MURS etc. I am sure the steel roof contributes to the good coverage. Just got to figure out something for HF. Thinking about running a 50' wire under the soffit hidden behind the bottom edge of the facial board.

 

[Ronnierozier2]

A mag-mount needs to be grounded to the same "ground plane" as the radio. In your case, the roof itself. The magnet only holds the antenna in place.

Not knowing if your roof is electrically connected to a 4' or longer ground rod literally into the ground around your home....I am not going to suggest a way to ground your antenna. Get a qualified and licensed electrician to insure both the cable ground lead and the roof are properly connected to the same electrical ground.

I can tell you with certainty that the roof isnt grounded. Never got around to doing it. Oddlyenough im an electrical engineer by trade working for a power generation company….no not Entergy lol

 

[donc13]

Not quite.

The magnetic mount antennas achieve their connection to the ground plane via capacitive coupling between the antenna base and the material it's sitting on. To RF, the small gap between the magnetic base and the roof (even if there's paint/powder coating) is virtually invisible to the radio. There's a very slight impact when comparing magnetic mount antennas to a permanent mount antenna, usually about 0.1dB of additional loss on the mag mount. 0.1dB isn't something that you'd hear with your ears, and it's not the cause of this problem. The issues with mag mounts usually arise when transmitting and there isn't a good DC ground. DC ground and RF grounds can be different things.

Grounding is good for lightning protection, and safety, that's why it's required by the NEC. For a temporary test installation like this, it's not going to make a difference.

I suspect the issue is the scanner front end getting swamped by a nearby 700MHz cell site. Grounding isn't going to fix that, and neither will installing a permanent antenna.

An RF filter that will have a sharp rolloff below the 700MHz LMR band would probably resolve the issue.
When you move away from your location, and proximity to the cell site, it's allowing your scanner to hear the system you want to listen to.
I've had this happen with other radios. I had an ADS-B receiver (1090MHz) completely swamped by a Verizon LTE site that we were sharing out tower with. I was able to fix it by moving the ADS-B receiver to one of my other sites.

Not exactly true. On a car, with a 12v powered receiver in it, the negative line is grounded to the vehicle frame and sheet metal. In a car with a self powered portable, the difference between a mag mount antenna and an NMO mounted identical antenna is easily 3db to 9db GREATER depending on frequency. On a conventional 150MHz channel from about 20 miles away (sitting in my driveway) I went from not hearing anything to loud and clear reception. Similar results on an 800MHz trunked system.

Mag-mounts and self powered receivers have zero connection between the vehicle frame (or steel roof) and the ground side of the cable attached to the portable's antenna jack.

I know this for a fact, I have tested it (several years ago) with a Larsen Tri-Band on a mag mount vs an NMO mount with my BCD-396T

 

[kb5udf]

I did a little more looking around. Site Map: Mississippi Wireless Information Network (MSWIN) Trunking System, Jackson, Mississippi
Looks like if you are in greenwood, there are 3 sites around you, but not particularly close. Your scanner might benefit from a directional antenna.
If cell/firstnet is the problem, an omnidirectional antenna won't help. But if you are a lucky a beam/yagi pointed at the right site, assuming there are no offending signals in that direction, may give better reception.

 

[mmckenna]

the difference between a mag mount antenna and an NMO mounted identical antenna is easily 3db to 9db GREATER depending on frequency.

You likely had other issues if you were seeing 3-9dB of difference.

 

[donc13]

You likely had other issues if you were seeing 3-9dB of difference.

Nope