BCD436HP/BCD536HP: Reception better lying flat

belvdr · Feb 21, 2018

Hello all,

Last night, I was playing with my 436 while debating what to do on, what appears to be, the simulcast issue.

I only have the Ohio MARCS-IP system programmed in, specifically Cincinnati and parts of Hamilton and Butler counties. I was picking up Cincinnati with no issue, but could not hear Butler County. I would see the alpha tag for Hamilton FD but no audio. Frustrated, I laid the scanner on its back to walk away and audio started pouring through. If I stood it upright, the audio disappeared.

Any thoughts on why this would occur? I can’t imagine a better antenna would help but I have been surprised in the past on how a good antenna can help.

brucebuck1010 · Feb 21, 2018

Yep, been there done that. Also, I've used 90 degree adaptors to get different angles on the antenna. Also used paper clips to various degrees. Used beam antennas mounted on a tripod. Its not about maximum signal strength. It's about trying to get a signal from only one tower. I'm in Mongomery Co OH, and I gave up on my 436 for MARCS. I now use a Unication G4 with almost perfect reception.

belvdr · Feb 21, 2018

brucebuck1010 said:
Yep, been there done that. Also, I've used 90 degree adaptors to get different angles on the antenna. Also used paper clips to various degrees. Used beam antennas mounted on a tripod. Its not about maximum signal strength. It's about trying to get a signal from only one tower. I'm in Mongomery Co OH, and I gave up on my 436 for MARCS. I now use a Unication G4 with almost perfect reception.

I'm also considering the same. It really hasn't performed well enough on MARCS to justify the cost.

pinballwiz86 · Feb 21, 2018

I don't have simulcast issues on my two local P25 systems, or in St. Louis when I travel..so this is an idea.

But, doesn't each P25 tower have it's own NAC code? Program that in to your scanner, so it ignores the simulcast from another tower on the same frequency.

jonwienke · Feb 21, 2018

belvdr said:
Frustrated, I laid the scanner on its back to walk away and audio started pouring through. If I stood it upright, the audio disappeared.

Any thoughts on why this would occur? I can’t imagine a better antenna would help but I have been surprised in the past on how a good antenna can help.

I some cases where there is a difference between simulcast tower signal strengths, but they are close enough in strength to cause interference, attenuating the RF signal just enough to push the weaker signal to the noise floor will improve the decode error rate. In your case, laying the antenna horizontal just happened to attenuate the signal just the right amount. A variable attenuator would allow you to adjust the attenuation amount to find the sweet spot between obliterating all of the towers' signals (too much attenuation) and having simulcast interference (not enough).

A better approach for a base station is to purchase a Yagi or similar directional antenna, and aim it so that you are primarily receiving a signal from one simulcast site. But of course that is not practical for handheld or mobile use.

jonwienke · Feb 21, 2018

pinballwiz86 said:
But, doesn't each P25 tower have it's own NAC code? Program that in to your scanner, so it ignores the simulcast from another tower on the same frequency.

Seriously?

Every tower in a simulcast system broadcasts the exact same data (including NAC) on the exact same frequency as every other tower. That is what causes the reception problem--identical signals from different towers arrive out of phase with each other, and interfere with each other.

belvdr · Feb 21, 2018

jonwienke said:
I some cases where there is a difference between simulcast tower signal strengths, but they are close enough in strength to cause interference, attenuating the RF signal just enough to push the weaker signal to the noise floor will improve the decode error rate. In your case, laying the antenna horizontal just happened to attenuate the signal just the right amount. A variable attenuator would allow you to adjust the attenuation amount to find the sweet spot between obliterating all of the towers' signals (too much attenuation) and having simulcast interference (not enough).

A better approach for a base station is to purchase a Yagi or similar directional antenna, and aim it so that you are primarily receiving a signal from one simulcast site. But of course that is not practical for handheld or mobile use.

Stuffing the yagi into the car is such a pain though.

So, aside from a yagi, a better rubber duck is likely not to help this, correct?

pinballwiz86 · Feb 21, 2018

jonwienke said:
Seriously?

Every tower in a simulcast system broadcasts the exact same data (including NAC) on the exact same frequency as every other tower. That is what causes the reception problem--identical signals from different towers arrive out of phase with each other, and interfere with each other.

Seriously.

belvdr · Feb 21, 2018

jonwienke said:
Seriously?

Every tower in a simulcast system broadcasts the exact same data (including NAC) on the exact same frequency as every other tower. That is what causes the reception problem--identical signals from different towers arrive out of phase with each other, and interfere with each other.

Calm down, man.

It's all good.

I think it is a valid question, because I do not have an intricate understanding of these systems. It's possible that guy/gal is in the same boat as me and is just trying to help.

jdolina · Feb 21, 2018

Have you tried setting the simulcast site to manual 8. I then go into analyze which helps find the best antenna placement. This has worked well for me with Marcs-ip simulcast sites.

belvdr · Feb 21, 2018

jdolina said:
Have you tried setting the simulcast site to manual 8. I then go into analyze which helps find the best antenna placement. This has worked well for me with Marcs-ip simulcast sites.

Manual 8? Are you referring to the threshold?

eorange · Feb 21, 2018

brucebuck1010 said:
Yep, been there done that. Also, I've used 90 degree adaptors to get different angles on the antenna. Also used paper clips to various degrees. Used beam antennas mounted on a tripod. Its not about maximum signal strength. It's about trying to get a signal from only one tower. I'm in Mongomery Co OH, and I gave up on my 436 for MARCS. I now use a Unication G4 with almost perfect reception.

I'm curious when you say you have almost perfect reception. I have 100% perfect reception with MARCS...what are you experiencing?

jonwienke · Feb 21, 2018

belvdr said:
I think it is a valid question, because I do not have an intricate understanding of these systems.

As a general rule, you should not offer advice unless you have an understanding of the subject matter. it generally causes more problems than it solves.

brucebuck1010 · Feb 21, 2018

belvdr said:
Stuffing the yagi into the car is such a pain though.

So, aside from a yagi, a better rubber duck is likely not to help this, correct?

Back when I was fumbling around with MARCS-IP on my 436, I pretty much had best results with the Miracle Baby antenna, made by Comet. Hope that helps!

-Bruce

belvdr · Feb 21, 2018

jonwienke said:
As a general rule, you should not offer advice unless you have an understanding of the subject matter. it generally causes more problems than it solves.

I agree, but sometimes one doesn't know that they don't know. At the same time, a perceived snarky response also causes more problems than it solves.

I appreciate the help.

brucebuck1010 · Feb 21, 2018

eorange said:
I'm curious when you say you have almost perfect reception. I have 100% perfect reception with MARCS...what are you experiencing?

Where I live (southern Montgomery County, OH), I am pretty much equidistant between two towers, so I get terrible reception with the 436 on Ohio MARCS-IP- I miss so much that it's not worth it. But the Unication P4 (with it's many limitations) works very well for me. YMMV

-Bruce

belvdr · Feb 21, 2018

brucebuck1010 said:
Back when I was fumbling around with MARCS-IP on my 436, I pretty much had best results with the Miracle Baby antenna, made by Comet. Hope that helps!

-Bruce

Thanks for the tip! I have heard good results from this one too:

https://www.universal-radio.com/catalog/scanants/6119.html

jonwienke · Feb 21, 2018

belvdr said:
Manual 8? Are you referring to the threshold?

Yes. 8 may or may not be the best setting. If you press the scroll knob, then Function, then the scroll again, the 436 will display P25 decode parameters, including the threshold level and decode error rate. Activate this display before you switch to Manual, and watch the threshold level to see where it is when you have the lowest decode error rate. That will be your best Manual threshold value.

jonwienke · Feb 21, 2018

brucebuck1010 said:
Back when I was fumbling around with MARCS-IP on my 436, I pretty much had best results with the Miracle Baby antenna, made by Comet.

The Miracle Baby is just a tiny antenna that attenuates the signal because it isn't very sensitive. IF you are located in a simulcast area where attenuation has a chance of helping, it may help if it attenuates the signal just the right amount. But the odds are that in most cases it will not help. A variable attenuator is more likely to be helpful because you can adjust the amount of attenuation. A directional antenna is even more likely to be helpful, except for mobile/handheld use.

belvdr · Feb 21, 2018

jonwienke said:
Yes. 8 may or may not be the best setting. If you press the scroll knob, then Function, then the scroll again, the 436 will display P25 decode parameters, including the threshold level and decode error rate. Activate this display before you switch to Manual, and watch the threshold level to see where it is when you have the lowest decode error rate. That will be your best Manual threshold value.

Awesome, thanks!

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