No 800 mhz reception

[RustyCivic]

Here's the story. I had the RS discone antenna up using rg-58u cable. It was a 50 ft. run of cable. I wasn't able to receive many of the freqs. that I wanted to hear. Reception in the 470 mhz and 800 mhz bands were just fair. A bad winter storm blew down the mast and antenna so I went out and bought the same antenna. This time I bought some LMR-400 cable and put it up in the same location. The difference in 470 mhz reception was like night and day. The stations that barely were making it through the squelch before were now coming in like stations just a city over. There is no doubt that the new cable was the reason. But, now, for some reason, I have absolutely no 800 mhz reception. It is like the coax isn't even connected to the scanner. I have to use the rubber duckie to hear 800 mhz now. Does anyone have an idea what might be happening here?
Thanks,
Dave

 

[k5uss]

It could be that your coax is shorted. Same antenna type, same location as prior, same radio that works on 800 with the duck... I'd ohm out the coax before I went any further.

 

[ka3jjz]

If not the coax, logic would suggest antenna damage of some kind, particularly since you mentioned a winter storm blew it down. A cracked connector, perhaps an element that's been broken - it could be any of several things. 73s and GL Mike

 

[RustyCivic]

Thanks for the responses. I've checked all connections for shorts etc. Everything is new..the antenna,connectors and cable. The antenna is in the exact same position. I think this is one of those questions that will remain a mystery. I may just have to put an antenna switch and switch to the duck for 800 mhz.

 

[N4JNW]

That's odd.... You actually went to a higher quality coax, and your 800 mhz reception degraded. That don't make a whole lot of sense..

I'd inspect that coax... An inch at a time.. Could be kinked? Maybe knicked? If just a little bit of the braid is knicked, it's letting out valuable RF that the antenna has collected..

 

[RustyCivic]

You are right. None if it makes any sense. I was really meticulous putting this antenna up. Making sure everything was perfect. I checked for shorts at different points of assembly....no shorts. There is nothing physically wrong looking at the antenna,cable or connectors. I have to stop thinking about it now. I feel a headache coming on.

 

[SkipSanders]

Well, the quick test is to connect a different antenna at the same spot with the same coax (even just your rubber duck, if you have suitable connector adapters) and see if THAT works.

If the antenna is good, there should definitely have been improvement, not degradation, of 800. The other possibility is that you have a very 'critical' signal spot around the antenna, where moving the antenna a few inches can change the signal drastically to at least one station. (That is, the new one might be in a very tiny 'dead spot' for the system you're trying to hear) Usually that wouldn't affect different 800 systems, though.

 

[N4JNW]

You are right. None if it makes any sense. I was really meticulous putting this antenna up. Making sure everything was perfect. I checked for shorts at different points of assembly....no shorts. There is nothing physically wrong looking at the antenna,cable or connectors. I have to stop thinking about it now. I feel a headache coming on.

Are you sure it's the antenna? Check out some newspapers and area news on the internet.. Make sure they're not moving the transmitter site or tinkering with power levels.. Eliminate the simple and easy stuff first. Make a list of everything you think it could be. Then, cross out the things that are the same, or that you're POSITIVE would not affect it.

After you've elimiated the simple, move to the complex, and do some digging. There is an answer... It might just take a little work to find it. It could be something simple, could be something you have no control over at all.

 

[DPD1]

If your basically listening to the same 800 system, I would normally say that it's just a coincidence and something happen to their system while your antenna was down. Or, maybe if you had a lot of trees nearby, it could have more of an adverse affect on 800 in the summer, as compared to winter. But what rules those out is that the 800 comes in on a handheld inside. There's no way you can get that inside on a handheld and NOT get it on the outside antenna, without there being something wrong somewhere. Either that, or there is some very peculiar null happening in that particular spot on the roof... But to that extent would be pretty weird. I would first try moving the antenna to a couple spots on the roof, or have somebody just hold it in a couple spots while you monitor. If nothing changes, there has to be something wrong somewhere. The electrical length in the coax can sometimes affect performance in a certain band a little, but it shouldn't do it anywhere near that much.

Dave
http://www.dpdproductions.com
- Custom Scanner, Aviation, MURS, GMRS, Marine & Ham Antennas -

 

[zz0468]

Does anyone have an idea what might be happening here?

Nope. Not a clue.

Check for continuity of both the center conductor and the shield from the radio end of the cable, all the way to the antenna elements, then look for shorts. Try the new coax with a clip lead or something and see what happens. Try the new antenna with the old coax. You can do some good trouble shooting with minimal equipment if you think logically.

 

[DaleRay]

Yes,use a Meter to see if You have the center and or the shield shorted out or if You have a Opening in Your Ant. system, check every bit of that system and rebuild the ant. or replace it,You may want to look at a new design for Your Ant. system or 2 ants one for Your low and one for your 800 with a switch at You base

 

[W6KRU]

I'm hoping he got that fixed already. :lol::lol:

 

[Jim41]

Here's the story. I had the RS discone antenna up using rg-58u cable. It was a 50 ft. run of cable. I wasn't able to receive many of the freqs. that I wanted to hear. Reception in the 470 mhz and 800 mhz bands were just fair. A bad winter storm blew down the mast and antenna so I went out and bought the same antenna. This time I bought some LMR-400 cable and put it up in the same location. The difference in 470 mhz reception was like night and day. The stations that barely were making it through the squelch before were now coming in like stations just a city over. There is no doubt that the new cable was the reason. But, now, for some reason, I have absolutely no 800 mhz reception. It is like the coax isn't even connected to the scanner. I have to use the rubber duckie to hear 800 mhz now. Does anyone have an idea what might be happening here?
Thanks,
Dave

If you have attenuation capability on your radio, try using it for your 800 mHz frequencies. You may have overload from a strong local signal.

Jim41

 

[W6KRU]

This thread was resurrected from 6/07 guys. You're not helping him at this point in time. IMO

 

[AlmostHandy]

You ought to check out heywhatsthat.com. Enter the parameters of the 800MHz site you're trying to monitor, and the parameters of your antenna's location and elevation, and check the visibility cloak to see what kind of reception you're area is getting. The site is kind of slow, so you have to be patient with it, but it's an awesome resource.

P.S. let me know if you have any questions about the site. I'm getting pretty good at using it. lol




EDIT: Just saw Dan's post, and I suppose I should really be getting into the habit of checking dates. sorry.

 

[kb2vxa]

OK, here we go with a small bit of techie talk. First of all I'll bet one cop to a box of donuts you used the Rat Shack cable which leaks like a sieve so you were picking up stray 800MHz signal with the coax, not the antenna. Now you're using quality cable that doesn't leak, the strays are gone.

A discone is rather deaf on 800MHz for the most part so now you're not hearing those signals from the antenna, you never were. Before the pedants jump all over me again I said FOR THE MOST PART, there ARE exceptions and those who tend to argue aren't in a weak signal area. Bottom line here is if you want good 800MHz reception shoot for an 800MHz antenna, most "broad band" scanner antennas are deficient on this band.

Naturally the 400MHz signals are now strong, RG58 exhibits so much loss up there I'm surprised you were hearing any at all. The higher you go in frequency the more loss ANY transmission line exhibits, that's why microwave systems use hollow wave guides and the antenna itself is in the equipment and not up on the tower. RG58 is just ducky for HF like 11M CB but when it comes to anything above 30MHz or so it sucks eggs.