BCD996P2: Significant Loss of Signal on a VHF P25 Simulcast System

Status
Not open for further replies.

Duster

CA/NV/KS/NE DB Admin
Database Admin
Joined
May 16, 2003
Messages
787
Location
Placer County, California
Hello,

I searched and could not find a previous thread about this, but I've heard a lot of chatter in the forums on the topic. I'd like to get some ideas on fixing it.

I monitor our local SO both for work and pleasure. They are on a countywide VHF P25 Simulcast, multi-zone system (Placer County, CA, CIRN in case you're wondering). It worked very well for a long time, but over the last year, I started to notice a loss in reception on the P25 side. I was a little slow to catch it, because they simulcast the primary dispatch channel on an analog frequency as well, which I usually monitor away from the truck, so I didn't catch the issue in a timely manner. It became readily apparent when I started focusing on the P25 system, because they were threatening to turn off the analog simulcast.

Here's what it is doing: It receives very well, as long as I am within 1/2 mile to a mile of an actual site. Once I get out past that range, I lose the P25 signal (I can tell by also monitoring the analog side). There are places where I will get P25 reception, but just in pockets, and sometimes from the mountain top zone, when I am clearly closer to a local tower. I think these are just ducting locations where I happen to get a really strong signal, like maybe it's overriding surrounding noise.

There has been a lot of mention in the forums that the 996P2 really chokes on monitoring simulcast VHF P25, and I've heard speculation that it has to do with overloading the receiver, heterodyne from multiple sites, etc etc etc. Anyone have any ideas on how to test and/or fix this? And if it is a known issue, is there a fix/patch in the pipeline?

Also, I monitor several P25 systems both here at home and over several states when I travel, and they seem to monitor fine (I don't have an analog backup to monitor, but I don't seem to lose conversation threads on them). BUT, they are all 700/800 systems, not VHF.

Ideas?

Thanks in advance.

David
 

Ronaldski

MI DB Admin
Database Admin
Joined
Aug 23, 2005
Messages
2,510
Location
Bay City MI
Have same radio as well. Assume you applied latest firmware to it?

Try items at my FAQ link 2,3,7,8,11,13 - I know #11 strange, but someway, somehow the connections get dirty, even in no smoking areas.
 

WoodburyMan

Member
Premium Subscriber
Joined
Dec 9, 2017
Messages
358
Location
Woodbury, CT
I'm interested in this as well. We have two repeater based (non trunked, but 2 site simulcast) and one simplex P25 VHF frequencies (152-155mhz) in my town. I have issues with all three P25 signals, where I will miss large chunks of conversations and the SDS200/100 I have cannot lock on. The Analog simulcast they have of one channel comes in just fine at -80db with no distortion.

I have tried every filter I can on it. No dice. Wide Normal seems to work the best. I've also played with my antenna setups a lot, many different antennas, and many different locations, with no improvement. I have P25 UHF and two 700-800mhz P25 systems I regularly receive no problem. It just seems to be VHF that has a problem.
 

iMONITOR

Member
Premium Subscriber
Joined
Sep 20, 2006
Messages
8,849
There has been a lot of mention in the forums that the 996P2 really chokes on monitoring simulcast VHF P25, and I've heard speculation that it has to do with overloading the receiver, heterodyne from multiple sites, etc etc etc. Anyone have any ideas on how to test and/or fix this? And if it is a known issue, is there a fix/patch in the pipeline?

Also, I monitor several P25 systems both here at home and over several states when I travel, and they seem to monitor fine (I don't have an analog backup to monitor, but I don't seem to lose conversation threads on them). BUT, they are all 700/800 systems, not VHF.

Ideas?

Thanks in advance.

David
What are you using for antennas, mobile and at home?
 

iMONITOR

Member
Premium Subscriber
Joined
Sep 20, 2006
Messages
8,849
I'm interested in this as well. We have two repeater based (non trunked, but 2 site simulcast) and one simplex P25 VHF frequencies (152-155mhz) in my town. I have issues with all three P25 signals, where I will miss large chunks of conversations and the SDS200/100 I have cannot lock on. The Analog simulcast they have of one channel comes in just fine at -80db with no distortion.

I have tried every filter I can on it. No dice. Wide Normal seems to work the best. I've also played with my antenna setups a lot, many different antennas, and many different locations, with no improvement. I have P25 UHF and two 700-800mhz P25 systems I regularly receive no problem. It just seems to be VHF that has a problem.
Same question...what antennas?
 

jonwienke

More Info Coming Soon!
Premium Subscriber
Joined
Jul 18, 2014
Messages
13,098
Location
VA
There has been a lot of mention in the forums that the 996P2 really chokes on monitoring simulcast VHF P25, and I've heard speculation that it has to do with overloading the receiver, heterodyne from multiple sites, etc etc etc. Anyone have any ideas on how to test and/or fix this? And if it is a known issue, is there a fix/patch in the pipeline?
It's a known issue, but there is no fix. Except for the SDS100 and SDS200, no scanner receives simulcast well consistently. It's not heterodyne, overloading, or whatever, it's the receiver not being designed to handle simulcast. Some models are less bad than others, but none are reliable or consistent.

I'm interested in this as well. We have two repeater based (non trunked, but 2 site simulcast) and one simplex P25 VHF frequencies (152-155mhz) in my town. I have issues with all three P25 signals, where I will miss large chunks of conversations and the SDS200/100 I have cannot lock on. The Analog simulcast they have of one channel comes in just fine at -80db with no distortion.

I have tried every filter I can on it. No dice. Wide Normal seems to work the best. I've also played with my antenna setups a lot, many different antennas, and many different locations, with no improvement. I have P25 UHF and two 700-800mhz P25 systems I regularly receive no problem. It just seems to be VHF that has a problem.
If you're having reception problems with the SDS models, then consider the usual suspects--overloading, poor signal quality, interference, etc. In your case, it sounds like there is a strong interfering signal nearby, or else you're using an indoor antenna and need to go to an outdoor antenna. VHF is more likely to have RFI from LEDs and household electronics than UHF or higher bands, and is more likely to be attenuated by metal in buildings. If you're using an indoor antenna and have a lot of computers and other electronics in your house, you're probably giving your scanner the RF equivalent of a Dutch Oven.
 

WoodburyMan

Member
Premium Subscriber
Joined
Dec 9, 2017
Messages
358
Location
Woodbury, CT
It's a known issue, but there is no fix. Except for the SDS100 and SDS200, no scanner receives simulcast well consistently. It's not heterodyne, overloading, or whatever, it's the receiver not being designed to handle simulcast. Some models are less bad than others, but none are reliable or consistent.


If you're having reception problems with the SDS models, then consider the usual suspects--overloading, poor signal quality, interference, etc. In your case, it sounds like there is a strong interfering signal nearby, or else you're using an indoor antenna and need to go to an outdoor antenna. VHF is more likely to have RFI from LEDs and household electronics than UHF or higher bands, and is more likely to be attenuated by metal in buildings. If you're using an indoor antenna and have a lot of computers and other electronics in your house, you're probably giving your scanner the RF equivalent of a Dutch Oven.
Indoor antenna most likely. The system I have setup is a 8 Element Directional Yagi for 700/800mhz beamed out the window, and a Diamont 19" HT antenna for VHF/UHF ham bands (tuned close enough to what I'm receiving...for the most part) taped to a window going to a Y adapter. I lose 3db or so vs each antenna by itself but gives me both bands well. The Yagi has *no* receive for anything under 400mhz or so, where it picks up some 400mhz+ plus very faint. I tried just my 2m/70cm antenna by itself, same results. My problem is more with distortion. There are two sites these 152-155mhz P25 signals are coming from, one site is 3.8mi away, but it's line of sight is blocked by two large hills. (450ft my elevation, 450ft at the site, but two 600-700ft hills in the way.). The second site is only 1.8mi from me, but is blocked by two LARGE hills immediately to my west that rise to 1,000ft+. Although I get analog, and it sounds fine, getting garbled P25 from two sites confuses the SDS for sure. It can handle distorted P25 from one site, but two may be too much. I have tried outdoor antennas with it to, same results. The only thing that worked was a Directional Yagi for 2m, pointed in a direction not directly at either site. I would be picking up scatter from one of the sites, with less distrotion somehow where it would work.

Oddly, my SDS100 can do this P25 distortion a little better than my SDS200.
 

jonwienke

More Info Coming Soon!
Premium Subscriber
Joined
Jul 18, 2014
Messages
13,098
Location
VA
Your yagi is probably picking up a reflection of the signal bouncing around the hill between you and the transmitter. Your problem isn't simulcast so much as the hills blocking the signal to your indoor antenna. Get it up on a pole outside, and things will work much better.
 

Duster

CA/NV/KS/NE DB Admin
Database Admin
Joined
May 16, 2003
Messages
787
Location
Placer County, California
Have same radio as well. Assume you applied latest firmware to it?

Try items at my FAQ link 2,3,7,8,11,13 - I know #11 strange, but someway, somehow the connections get dirty, even in no smoking areas.
Yep, most current firmware, all updates are present. I'll check out your FAQ page. Thanks!
 

Duster

CA/NV/KS/NE DB Admin
Database Admin
Joined
May 16, 2003
Messages
787
Location
Placer County, California
What are you using for antennas, mobile and at home?
I should have added this...

This is a mobile install. Mounted in a 2007 Tahoe, with a good professional grade tri-band (VHF/UHF/800) antenna, permanently and professionally mounted on the rear roof. I don't remember the brand of the antenna, but it came highly recommended by my local techs for monitoring from CHP Lowband to the local P25 800 systems. And except for this single system, it has worked as advertised.
 

jonwienke

More Info Coming Soon!
Premium Subscriber
Joined
Jul 18, 2014
Messages
13,098
Location
VA
Simulcast is the problem, and the only solution is to replace the 996 with a SDSx00 model. Especially if all the non-simulcast traffic comes in fine. Being close to a transmitter means all the other transmitters on that frequency are drowned out, and you're effectively no longer simulcast.
 

WoodburyMan

Member
Premium Subscriber
Joined
Dec 9, 2017
Messages
358
Location
Woodbury, CT
I should have added this...

This is a mobile install. Mounted in a 2007 Tahoe, with a good professional grade tri-band (VHF/UHF/800) antenna, permanently and professionally mounted on the rear roof. I don't remember the brand of the antenna, but it came highly recommended by my local techs for monitoring from CHP Lowband to the local P25 800 systems. And except for this single system, it has worked as advertised.
Do you happen to know what model antenna?

I'm looking for a good VHF/UHF/800 to eventually mount outside as a base antenna. (Adding a ground plane kit to them of course if they're mobile antennas).
Your yagi is probably picking up a reflection of the signal bouncing around the hill between you and the transmitter. Your problem isn't simulcast so much as the hills blocking the signal to your indoor antenna. Get it up on a pole outside, and things will work much better.
Yeah that's my thoughts. It's just strange the analog simulcast from the same sites come in -80db or so with an indoor, and even the P25 VHF comes in -85 to -90db, but the SDS100/200 just can't get a lock on them. It's some weird combination of signal blocking and probably getting simulcast distortion from both sites. The directional blocks it out so I'm only getting a singe site, plus it gives me a better signal on the single site. Eventually I plan on mounting something outdoors, I need a VHF/UHF antenna for local amateur repeaters too that could double when I'm not TX'ing which would be 99% of the time. I shut my scanner off whenever I'm TX'ing too to save the receiver on the SDS's...
 

jonwienke

More Info Coming Soon!
Premium Subscriber
Joined
Jul 18, 2014
Messages
13,098
Location
VA
Shutting the scanner off during TX is pointless. The same antenna voltage hits the protection diodes and first stage RF amplifier transistor whether the scanner is on or off. And those are what fry from excessive input voltage.
 

JWJ

Member
Joined
May 15, 2005
Messages
10
Location
Centreville, AL
The following is the type of info that makes me enjoy Radio Reference,com forums and reminded me to make sure I was paying my dues. (occasionally I will let my premium membership lapse) Thank you

The same antenna voltage hits the protection diodes and first stage RF amplifier transistor whether the scanner is on or off. And those are what fry from excessive input voltage.
 

WoodburyMan

Member
Premium Subscriber
Joined
Dec 9, 2017
Messages
358
Location
Woodbury, CT
Do you happen to know what model antenna?

I'm looking for a good VHF/UHF/800 to eventually mount outside as a base antenna. (Adding a ground plane kit to them of course if they're mobile antennas).

Yeah that's my thoughts. It's just strange the analog simulcast from the same sites come in -80db or so with an indoor, and even the P25 VHF comes in -85 to -90db, but the SDS100/200 just can't get a lock on them. It's some weird combination of signal blocking and probably getting simulcast distortion from both sites. The directional blocks it out so I'm only getting a singe site, plus it gives me a better signal on the single site. Eventually I plan on mounting something outdoors, I need a VHF/UHF antenna for local amateur repeaters too that could double when I'm not TX'ing which would be 99% of the time. I shut my scanner off whenever I'm TX'ing too to save the receiver on the SDS's...
Well, between using IFX, turning filter OFF, and getting a new VHF/UHF antenna.. it seems to work. I got a fairly large mobile antenna, NMO mount, thats 2.5ft tall thats tuned specifically for MURS and GMRS frequencies, just about the HAM band, right near the frequencies I want to hit. Anything outside that it blocks. For now I have a metal base on it, but plan to get a actual ground plane hit and mount it outside. But I just got P25 signals from the local repeater fine and dandy. It doesn't get any 700/800mhz bleed over to interfiere with the directional 700/800 Yagi i have it Y'd into.

Shutting the scanner off during TX is pointless. The same antenna voltage hits the protection diodes and first stage RF amplifier transistor whether the scanner is on or off. And those are what fry from excessive input voltage.
Eeep. Alright, then looks like I'll be pulling the antennas as well. Thanks!
 

jonwienke

More Info Coming Soon!
Premium Subscriber
Joined
Jul 18, 2014
Messages
13,098
Location
VA
I don't know what maximum RF power input the scanner can handle, but it's at least 250mW. I measured the bleedover in my truck using a watt meter and a dummy load connected to the scanner antenna cable when I keyed up, and it varies by band, but isn't more than that.
 

Duster

CA/NV/KS/NE DB Admin
Database Admin
Joined
May 16, 2003
Messages
787
Location
Placer County, California
Do you happen to know what model antenna?

I'm looking for a good VHF/UHF/800 to eventually mount outside as a base antenna. (Adding a ground plane kit to them of course if they're mobile antennas).
Sorry for the delay replying to this. I haven't been on in a while.

The antenna I'm using is a Comet SBB-14 Tri-Band Ham Radio antenna. That antenna has been discontinued, and the current model is a Comet SBB-15...runs about $80-85. I like that it works very well across the bands...of particular note to me is that it receives Low-Band almost as well as my dedicated TK-690 Low Band Radio, and receives 700/800 trunked systems very well also. It is an excellent receiver antenna across all bands.

Link to my vendor below:

 

WoodburyMan

Member
Premium Subscriber
Joined
Dec 9, 2017
Messages
358
Location
Woodbury, CT
Sorry for the delay replying to this. I haven't been on in a while.

The antenna I'm using is a Comet SBB-14 Tri-Band Ham Radio antenna. That antenna has been discontinued, and the current model is a Comet SBB-15...runs about $80-85. I like that it works very well across the bands...of particular note to me is that it receives Low-Band almost as well as my dedicated TK-690 Low Band Radio, and receives 700/800 trunked systems very well also. It is an excellent receiver antenna across all bands.

Link to my vendor below:

Thank you sir!

I actually found out the problem I had was because of my dual antenna setup. I had a direction 8 element yagi for 700/800mhz going into a splitter/combiner with my Diamond 140mhz/440mhz antenna. The Diamond picked up SOME of the 700/800mhz as well, very weak, and was causing the distortion. I use a duplexer I had for my HF rig that splits a antenna into HF+6m and VHF/UHF (1.3mhz to 90mhz and 125mhz-470mhz) and connected just the 125mhz-470mhz side to my splitter, and it works as a band filter to get the High-UHF 700/800mhz signals out.
 

jonwienke

More Info Coming Soon!
Premium Subscriber
Joined
Jul 18, 2014
Messages
13,098
Location
VA
You don't want to use a splitter for that sort of thing, you want a diplexer to ensure that only one antenna's signal is present in the output at any given frequency.
 
Status
Not open for further replies.
Top