SDS100/SDS200: SDS100 Overload

[xusmarine1979]

Hi all, hope all is well.

Does anyone know the approximate db range that the radio becomes overloaded by a signal? Or how many db it takes to reduce the overload?

I listen to Ohio MARCS mostly, Stark and Summit County's 700/800MHz system and a handful of smaller FD's on UHF. So since both county's I listen to are simulcast, I'm thinking about tuning an antenna more toward UHF since the radio seems to overload more on 800. 700 and below seem mostly fine.

I've tried the various filters, IFX and whatnot, but I think I'd prefer a stubby antenna that may help on 800.

I know I can use the attenuator, but at times I do have a weaker signal in bigger buildings and just isn't practical for me.

So what I'm aiming for is a stubby that will keep UHF and 700 good, yet reduce 800 just enough that it'll help with the overload.

So... any thoughts?

 

[tvengr]

I know I can use the attenuator, but at times I do have a weaker signal in bigger buildings and just isn't practical for me.

Are you aware that you can use the attenuator by system, site, or frequency? You can turn it on and off from the keypad.

 

[xusmarine1979]

It certainly helps when I'm directly by a cite or cell tower, but as I stated it simply isn't practical for me. It kinda sucks because I literally work by one of the MARCS sites, but at times I take the back roads surrounded by corn to and from work, the signal unfortunately isn't as strong so I lose it from time to time.
So that's why I figured a UHF antenna may help a bit on 800 yet still keep everything below at a decent level.

 

[wtp]

why not make two systems, one with attenuation and one without ?
then turn it on or off as needed.

 

[xusmarine1979]

Once again, this is not practical while driving.

If someone could actually answer my question, I would be grateful.

 

[Randyk4661]

If the signal is strong using a de tuned antenna isn't going to help much. Even if you were to use a low band antenna (30-50 Mhz) it would help a little. Once you got on the road it would likely cause you to not hear weaker signals on 800. A 450-460 antenna is closer to a half wave to 800Mhz and could also hinder the results you seek. Even if you were to take the antenna off completely, sitting under a strong site could still overload the radio. Public safety can use some high power for their transmitters in rural areas, not so much for urban areas. We are still talking close to 50 watts with possibility of over 100 watts for these sites.
I have to agree with wtp, make two lists, one attenuated and one not. While you are at your job site use the attenuated FL and before you leave switch to the other FL.
Good luck with what you decide but I don't think using a de tuned antenna for 800Mhz is going to help much.
Randy

 

[wtp]

for changing while you drive, use GPS to turn things on and off.

 

[phask]

Once again, this is not practical while driving.

If someone could actually answer my question, I would be grateful.

Cold turn on / off with 2 key presses if 2 different fav. lists.

 

[Ubbe]

Does anyone know the approximate db range that the radio becomes overloaded by a signal? Or how many db it takes to reduce the overload?

I would say it starts to go bad at -65dBm. But the receiver has internal spurious signals that acts as a mixer and when I receive a -90dBm signal I can hear that signal a couple of 100kHz away at a -105dBm level. So the receiver have problems even at the lowest signal levels. If you keep all signals below -95dBm you should not hear those mixed signals as they are below the sensitivity of the receiver.

/Ubbe

 

[xusmarine1979]

Thank you for answering my question, Ubbe. Exactly what I was looking for.

Thank you all for your suggestions, and I assure you that I've already attempted them all. Driving a new Jag I'd rather not run excessive wires or mount anything.

Moderators, feel free to close the thread.