Feedback issues

[kyparamedic]

I hope this is the right forum, I wasn't sure where else to put this. I work for two different services, one of which uses an 800 MHz EDACS system and another that uses conventional VHF. On the VHF radios, it seems that if we're even in earshot of another radio on the same channel, we get major feedback. On the EDACS system though, it seems that the other radios have to be turned up really loud or you have to be right next to it to get any feedback. Is this just my imagination or do 800 MHz systems have less feedback issues? Why is this? Also, if there were to be a slight offset or delay in the transmission such as when you're talking on a cellphone and listening to yourself on the other end, would this eliminate feedback or would it still occur?
Thanks.

 

[scanfan03]

I hope this is the right forum, I wasn't sure where else to put this. I work for two different services, one of which uses an 800 MHz EDACS system and another that uses conventional VHF. On the VHF radios, it seems that if we're even in earshot of another radio on the same channel, we get major feedback. On the EDACS system though, it seems that the other radios have to be turned up really loud or you have to be right next to it to get any feedback. Is this just my imagination or do 800 MHz systems have less feedback issues? Why is this? Also, if there were to be a slight offset or delay in the transmission such as when you're talking on a cellphone and listening to yourself on the other end, would this eliminate feedback or would it still occur?
Thanks.

Feedback has nothing to do with the frequency. I think it is just how loud the repeater is on the VHF channel versus the 800 MHz channel. You also have to look at how loud you were talking on each radio. If you put a delay on, it will cause an echo and then feedback (depending on how long the delay was).

 

[kyparamedic]

Ok, thanks for the explanation. So the repeater can actually be set for a higher volume? I don't completely understand this but I don't know a whole lot about radios. On the VHF system, just keying up the mic anywhere near other radios causes horrible feedback unless the others are turned down to an almost inaudible level. I've just noticed that there seems to be less feedback issues on 800MHz systems.

Thanks.

 

[scanfan03]

Ok, thanks for the explanation. So the repeater can actually be set for a higher volume? I don't completely understand this but I don't know a whole lot about radios. On the VHF system, just keying up the mic anywhere near other radios causes horrible feedback unless the others are turned down to an almost inaudible level. I've just noticed that there seems to be less feedback issues on 800MHz systems.

Thanks.

You have to look at how loud you were talking into each radio. Also, in my county (this isn't a rule) the trunked is a lot quieter than the local VFD's conventional, sometimes.

 

[kyparamedic]

Is the repeater volume some type of independent setting? I just know that it seems that if another radio is even in earshot when we are transmitting there is awful feedback. Maybe it has to do with the sensitivity of the mics. The police operate off a separate repeater and it seems that they are able to stand pretty close to each other and transmit without problems although sometimes the other officers cover up their mics. Most of them use the same radios that we do however.

 

[N_Jay]

It also could be that in the EDACS system (or radios) there is some digital audio processing that adds a slight delay, minimizing the chance of feedback.