Frequency problem

[chad_96]

I have a frequency that I have noticed is causing a lot of garble. Of the 9 frequencies within the site, this 1 frequency is the only frequency that is consistent with garble and 100+ on D-errors.

I would assume that this problem is being caused by interference of some kind. What I can't find information on is if this would be something to try and do 1 of 2 things with. 1st being using IFX, if that's something that IFX could possibly help. 2nd, since it's not labeled a control channel, I'm curious as to if that channel can be removed from the frequencies, without causing an issue with receiving?

That specific frequency is used a fair amount as well as a couple others I noticed. However, I'm not sure on what can be done to try and either remedy the issue, or if it can just be removed without issue?

For reference, I will attempt to load the image with the frequency (851.450) highlighted. This is on the La Junta Site in Otero County, Colorado and on the Colorado DTRS statewide system.

 

[ScannerSK]

I've noticed the same at my location, that specific voice channels are harder to decode than others. This could be due to any number of reasons. It could be due to interference however that would likely affect the users on the system as well so that may not be the actual cause unless the interference is very localized in nature.

The control channel tells the scanner which voice channels to tune into to receive the desired traffic. There is no way to turn off a specific voice channel on a P25 system. You could use a different control channel if another tower/site is usable in your area which would have a different set of voice channels.

The most likely thing to help is repositioning the scanner/antenna. I reposition my scanner while the problem voice channel has live traffic being carried on it to obtain the best reception.

Other things to try would by the IFX as you mentioned or adding the attenuator to that site. Keeping the squelch turned down as much as possible, typically 2 on most Uniden scanners, may help and adjust decoding settings (P25 decoding threshold, etc.) if the scanner has them.

You could even try using multiple antennas tied into the scanner input or a directional antenna such as a Yagi if feasible in your situation.

Shawn

 

[chad_96]

I've noticed the same at my location, that specific voice channels are harder to decode than others. This could be due to any number of reasons. It could be due to interference however that would likely affect the users on the system as well so that may not be the actual cause unless the interference is very localized in nature.

The control channel tells the scanner which voice channels to tune into to receive the desired traffic. There is no way to turn off a specific voice channel on a P25 system. You could use a different control channel if another tower/site is usable in your area which would have a different set of voice channels.

The most likely thing to help is repositioning the scanner/antenna. I reposition my scanner while the problem voice channel has live traffic being carried on it to obtain the best reception.

Other things to try would by the IFX as you mentioned or adding the attenuator to that site. Keeping the squelch turned down as much as possible, typically 2 on most Uniden scanners, may help and adjust decoding settings (P25 decoding threshold, etc.) if the scanner has them.

You could even try using multiple antennas tied into the scanner input or a directional antenna such as a Yagi if feasible in your situation.

Shawn

Hey, thanks for the reply.

I have tried the attenuator, as I have just installed a 800mhz vertical antenna on a mast outdoors, and after reading and sampling/testing found the attenuator helps tremendously on my local and closest site of the 2 sites I monitor.

After working through sampling filters for the 2nd site, I found the filter that works great, but, that 1 frequency is giving me a hard time and is one of the voice channels used 50-60% of the time, and the only frequency I noticed to have the massive garble and huge D-Error rate.

I've seen where some people have mentioned removing voice channels, but never seen much as to what the outcome would be by doing so. Just that it was not a good idea. My intuition would be to try the IFX setting on that particular frequency as it could be from interference. Haven't had a chance to try it yet however.

Wasn't sure if others had noticed an issue with a frequency though, and thought I would see what type of advice or remedies are out there to attempt to get it fixed or better of nothing else.

There is 1 site in that area, but it's further from me, which I don't think would be an issue reaching with this new antenna as I receive stuff from 40 miles away and that site is roughly 18-20ish miles away versus the 16ish that I currently use from that area.

Anyhow, thanks for the information and advice!

 

[chad_96]

Deleted all the channels labeled in black as I'm told they are not needed at all because the system computer will automatically assign them.

Not sure if that would cause any type of interference or issues with having them programmed in or not. Will do some testing and see if there's any change now that I removed that frequency as well as the other black listed frequencies, and then try adding them to the IFX add list in Sentinel if not.

 

[BinaryMode]

If your scanner is capable, try changing the IF for that one frequency. It can be done in the ProScan software where you add the individual frequencies.

Intermediate Frequency Exchange - The RadioReference Wiki

wiki.radioreference.com

Example for a P2 scanner: Easier to Read BCD325P2 Digital Scanner Manual

Edit-

Yeah, what was said above 9 minutes ago.

 

[ScannerSK]

No difference should be noticed. Uniden scanners just lock onto the first site frequency that has control data being broadcast on it and then proceeds to ignore all the other frequencies. The only exception is when the data stops being received and then the scanner will attempt to find another frequency with control data being broadcast on it.

 

[wtp]

from the manual
Intermediate Frequency Exchange for a conventional channel on or off
so it would not be able to do anything on a trunked system.
the one thought i had is that there might be a birdie on that freq.
take the antenna off and set up a custom search to cover that frequency. (851.4 to 851.5)
if you get an open mic sound on it, that would be it.

or the quick way, depending on the model,
take the antenna off,
when scanning hit the hold button, type in 851.45 and hit hold again.

 

[chad_96]

from the manual
Intermediate Frequency Exchange for a conventional channel on or off
so it would not be able to do anything on a trunked system.
the one thought i had is that there might be a birdie on that freq.
take the antenna off and set up a custom search to cover that frequency. (851.4 to 851.5)
if you get an open mic sound on it, that would be it.

or the quick way, depending on the model,
take the antenna off,
when scanning hit the hold button, type in 851.45 and hit hold again.

Thanks for sharing that. I couldn't find much, of description, pertaining to exactly what IFX did. Just that most threads mention it didn't work for them.

I will give your advice a try and see what I come up with.

Thank you

 

[RMason]

I recall you have the sds100. To better understand the scope of the issue, you may want to take the sds100 close to LaJunta to help determine if the issue is dependent on your location (weak signal, local interference, obstruction from the mesa, etc).

 

[chad_96]

I recall you have the sds100. To better understand the scope of the issue, you may want to take the sds100 close to LaJunta to help determine if the issue is dependent on your location (weak signal, local interference, obstruction from the mesa, etc).

Yes, and have finally got it dialed in, the best I can.

This issue is on the SDS200 I finally got set up. Running a 800mhz vertical antenna with LMR-400 coax and a 4' LMR-240 ultra flex jumper.

Works great minus the 1 frequency on the La Junta Site that gives a lot of garble and D-Errors get up to 100+ in a few seconds.

Other than that, thing runs great. Am getting ems/fire from 40 miles away like it's next door clear as a bell.

 

[tvengr]

Try using the 4 red control channel capable frequencies only. All of the frequency info is carried on the control channel. Delete the other frequencies. The 851.45 frequency may be a data frequency which the scanner is mistakenly trying to use as a control channel. Try using all of the filters to see if any solve the problem. Avoid using the Auto filter. It will slow down your scanning. Try using IFX on the 851.45 frequency. In the Sentinel profile editor, you can set a list of frequencies for IFX under the Miscellaneous tab.

 

[chad_96]

Try using the 4 red control channel capable frequencies only. All of the frequency info is carried on the control channel. Delete the other frequencies. The 851.45 frequency may be a data frequency which the scanner is mistakenly trying to use as a control channel. Try using all of the filters to see if any solve the problem. Avoid using the Auto filter. It will slow down your scanning. Try using IFX on the 851.45 frequency. In the Sentinel profile editor, you can set a list of frequencies for IFX under the Miscellaneous tab.

Yes, I deleted all but the red channels last night. I had totally misunderstood and thought I had read that those channels should be programmed. So I'm going to run it today with that change and see how it does.

As far as filters, I have noticed that when it comes to 800mhz systems, the WIDE filters seem to be the best to go with. I am going to run both of them as well and see. Wide invert seemed to be the best, though. Minus that frequency that was giving me trouble. I was more so wondering if maybe me having that frequency programmed was causing issues as the control channel was also assigning it as the voice channel through the data. But it didn't do it with other voice channels.

Anyways, IFX as I'm told will do nothing for me as I am monitoring a trunked system (post #7) I thought about trying it to see what if any difference it made for me initially, before I was given that information.

 

[tvengr]

Anyways, IFX as I'm told will do nothing for me as I am monitoring a trunked system

IFX can eliminate interference on a conventional frequency as well as on a trunked frequency in a site. I often have good results with the wide invert filter.

 

[chad_96]

IFX can eliminate interference on a conventional frequency as well as on a trunked frequency in a site.

Hmm.. well I guess if it can possibly eliminate interference on a trunked frequency I need to get in gear and try it for the sake of trying.

I have monitored for a couple hours and noticed other than that frequency, I get 0-10 D-error on the other frequencies (voice channels), mostly 0. So I would assume by what I've read and seen, interference is more than likely a cause to that situation, in one form or another.

Thanks for the advice, I'm going to try to get that programmed with the IFX this afternoon and see what happens.

 

[tvengr]

Does the interference disappear when you leave the house? Another thing to try is to unplug other electronic devices in the house. USB switching power supplies can generate wideband interference. It could be a computer or even the local oscillator on another scanner or receiving device radiating a signal.

 

[chad_96]

I have a television and stereo on the same room. TV is wifi enabled. Tried unplugging it and the radio. Figured the wifi could be interfering with the frequency possibly. Nothing notable changed. What I have found today is that the same frequency isn't as bad, as the D-errors take longer to add up and cause thr garble. But overall same.

It seems that the frequency in question is the most used voice channel the system is picking. I would say 70% of the time. And out of every 10 transmissions on that frequency, 7 of the 10 times it garbles and has high D-Error rates. The other 3 times there will be 0 D-Error on that same frequency.

I'm thinking the only thing to do is try IFX on that frequency, and if that doesn't do anything, it is just the way it is and nothing different can be done, but accept it as it works. I just think there's interference as often as it does. I know that that's just the way a scanner operates, and won't be 100% perfect. But I still believe it can be less often and better, possibly...

Edit -
Also, the scanner in question is an SDS200 and I don't use it mobile. I am using a dpdproductions outdoors 800mhz vertical antenna mounted on mast.

 

[BinaryMode]

Is the correct modulation set?

What I would do is try another scanner if you have one or an SDR with a trunk tracking program like SDRTrunk or OP25 or DSD+. See if that frequency is still a problem. If it isn't then the firmware of the scanner may need to be updated or the scanner is bad.

Do you have a multimeter? Select the continuity or ohm setting and measure the middle connector and outside of the cable connector. If there's continuity or an ohm reading your coax cable or antenna may be the issue.

NooElec or RTL-SDR are the popular cheap SDRs that'll work.

I'm curious as to if that channel can be removed from the frequencies, without causing an issue with receiving?

No. That's a voice channel/frequency. And sometimes control channels/frequencies can be a voice channel. I've seen this in my ProScan history log where the control channel changed frequencies. Doesn't happen often but can. Even if you use control channel only monitoring, the scanner will tune to that problematic frequency as it's a voice channel.

 

[chad_96]

Got the issue figured out and fixed. Been up and running all day without issue. Frequency that was troublesome is now performing very well, along with the others. Little to no D-error, have noticed no garble today on anything minus a little that started to and then corrected itself.

Thanks for everyone's help and advice.

Chad

 

[RMason]

Got the issue figured out and fixed.

Glad to hear. What was the issue and fix?

 

[chad_96]

Glad to hear. What was the issue and fix?

Well first, I noticed that of what seemed like an endless sea of forum posts inread there was 1 common theme.

That theme when it pertains to 800mhz systems always ends with a filter setting in the "Wide" selection. After having Wide invert work best, I had 1 frequency that was just giving me hell. Seconds into a transmisson D-Error shot up 100+, garbled and seems the system always picked that frequency.

After talking with some people who messaged, and giving me insight and advice, I sat here all day re-testing every filter, and noting everything I could.

End result was..I was using the correct filter the whole time for that troubled site. I turned the Attenuator on with that filter, and haven't noticed a problem since, minus a few little garbled transmissions that correct themselves. Picking up radio traffic from 40 miles away crystal clear as well!

Now to shorten the 60' of LMR-400 coax to the 20' that I need in my end setup...if I can find someone in my area that knows how, that is...