800 MHz simulcast

Viking · Post by **Viking** » Fri Aug 27, 2004 9:20 am

Any simulcast experts out there????

I have been playing a little with our 800MHz simulcast system. When I listen to it while driving (older Motorola spectra radio) it has a crackling noise. It sounds fine when I am sitting still.

thebigphish · Post by **thebigphish** » Fri Aug 27, 2004 9:37 am

do other vehicular mounted RXers sound ok? do stationary units in buildings sound ok? i'd be more inclined to think that it's a RX problem on your unit.

and...how is the simulcast set up? a few more details....

Post by **xmo** » Fri Aug 27, 2004 11:38 am

A certain amount of 'crackling noise' is going to be present when driving through simulcast overlap areas. A significant amount of 'crackling noise' and other audio distortions in overlap areas are classic signs that the system is due for optimization.

Contact the system support techs and tell them your experience. They will know the system well enough to tell you if what you are hearing is normal or indicates a problem. They might appreciate the heads up - but I would still recommend a cautious approach - don't start out by telling them their system is all hosed up - just tell them your experience and see what they say.

abbylind · Post by **abbylind** » Fri Aug 27, 2004 1:05 pm

Yep, we have a 800 simulcast here
On the freeways when you are moving along you can hear the "bacon frying" in the background on analog transmissions
On digital transmissions its quiet.
Nature of the beast.
Fowler

Post by **batdude** » Fri Aug 27, 2004 8:48 pm

and i used to think i was on crack while driving around in whorelando florida

lol

i thought my spectra was goin' nutz

doug

N4DES · Post by **N4DES** » Sat Aug 28, 2004 2:51 am

Noise is typical with simulcast. You will also find that it will move with conditions. In the mornings I drive daily thru an overlap area on the way to work, on the way home in the afternoon on the same road no simulcast chatter.

Some of our users don't like it but when I explain to them the benefits of simulcast they agree that it's something that they can live with.

As long as it doesn't distort or override the target audio I wouldn't worry about it.

nmfire10 · Post by **nmfire10** » Sat Aug 28, 2004 4:12 am

I rather have a little noise instead of nothing. Are the effects the same if you used UHF Simulcasting?

Cam · Post by **Cam** » Sat Aug 28, 2004 3:00 pm

nmfire10 wrote:I rather have a little noise instead of nothing. Are the effects the same if you used UHF Simulcasting?

Yep, the noise comes from the two or more signals being rx-ed by your radio and the timing being some what off. The band has nothing to do with this.

Cam

bernie · Post by **bernie** » Sat Aug 28, 2004 10:33 pm

My two bits worth:
The noise while you are moving.
On single site systems in areas where the signal from the site is not full quieting you will hear a tone if driving directly to or from the site.
This is a known feature.
On lower frequency systems this is a fluttering sound.
This is why EDACS has a problem at about 14MPH under these conditions.
The tone interfers with the signalling.
This is most likely normal for your system.
The key is moving. As I understand it you are moving through "standing waves".
If there was a sync, or phasing problem it would occour while stationary.

My observation: In simulcast systems there will always be areas where coverage is difficult or impossible.

Viking · Post by **Viking** » Fri Sep 03, 2004 4:04 pm

Thanks for your inputs.

The reason why I posted the question was, that I have a few 150MHz simulcast channels, that dont have the crakling. They have overlap zones, but they dont have the cracling when you drive.

I was thinking that it has something to do with the difference in wavelenght???

bernie · Post by **bernie** » Fri Sep 03, 2004 5:10 pm

My two bits worth:
Yes, that is my theory.