A Signal Problem...

[RANGERDALEXP]

O.k., Here is the problem at hand. A couple of months ago I added another scanner to my Uniden 996xt scanner collection and it is a Uniden BCT15x so I can monitor LASD incoming mobile broadcast. It is tied to one antenna using a SP1300 combiner splitter. Everything did worked well but I wanted to gain some gain for weaker signals so I then decided to install a new discone antenna to receive better. Everything worked well for a few days after the install but then I started to notice that the dispatch and then the strong mobile signals started to sound broken up and distorted and was slight at first and has progressively gotten worse on both scanners since then. I have played with the attenuators on both scanners and it makes no difference. Also the signal meters show good signal. I have also tried removing the SP1300 to see if that was the problem and nothing changed. The only clear signals are from the next county but LASD and LACF have issues on dispatch and close mobile units. Could this be a problem with a bad connector at the antenna? I would think if the signal meters show good signal that this would not be the case. I am at a loss and any Ideas on what would cause this problem would be great……Thanks

 

[prcguy]

It sounds like the major change before the problem is the new antenna. Try using the attenuator on the scanner (if it has one) and see if that clears things up. If so you could have a overload issue.
prcguy

 

[RANGERDALEXP]

It sounds like the major change before the problem is the new antenna. Try using the attenuator on the scanner (if it has one) and see if that clears things up. If so you could have a overload issue.
prcguy

Thanks, Like I had mentioned in the post that the attenuators had no affect on the breaking up and crackling problem. With them on you can see the signal meter float up and down but when they are off, it holds a steady 5 bars all the time during the broadcast. The kern county dispatch seems to come in clear but as for LASD and LACF the problem has become a real issue. Also when the dispatch is on you can hear a slight popping sound during the broadcast.......

 

[prcguy]

Aah, I missed the attenuator part.

Are the mobiles you mention going through the same repeater as the base or are you receiving them direct?

If their all through the same repeater and the system is simulcast it could be a problem like I had with LAPD when they were still analog. I'm apparently between a few simulcast transmitter sites and LAPD would usually have a slow fading distortion like phase distortion when listening to VHF lo-band FM via skip.

I would have this problem most of the time at my house and in my driveway but when I drove down the street a little the problem cleared up. There were also a few intersections in town that caused the same problem.

If the system you are having problems with is not simulcast or you are hearing the mobiles direct then I would need more info, otherwise it doesn't sound like an antenna problem to me at this point. Maybe someone else might recognize the problem and chime in.
prcguy

 

[RANGERDALEXP]

The mobile units I think do use a repeater when they operate on the L-Tac and C-Tac bands. On the dispatch in bands I know they run at a much lower wattage and I do not think they operate on a repeater. I can only here those cars 2 to 5 miles away which is kind of a let down and is why I changed antennas to get better gain. The dispatch out runs through repeaters and a much higher wattage.

I did not have this problem with the old antenna and it only started to happen a few days after the new one went up. The antenna is not a new one and is the one I used in the SF Valley 12 years ago. The antenna is about 20 years old and it is the old style Radio Shack Discone that is no longer made today . It is in like new condition and worked real well back in the day.

The antenna is mounted at around 30 feet and a bit hard to get too. I just find it a bit hard to believe that it worked well for about 48 hours then went down hill from there. I had metered the cables before it was installed and it checked out good at the time. The run is around 60 feet +- 5 feet useing Radio Shack Cable RG 58. I would have preferd to use Beldon but there is no such thing as a good radio supply house in the AV and hate doing mail order......

 

[RANGERDALEXP]

I want to say thank you prcguy for being the only one to try to help with this problem. I thought more people would have more input or ideas but I guess not. even though the problem is not fixed I have come up with a strategy that I will do sometime next week. I am going to replace all the cable with new beldon cable. If that does not fix the problem I will then be forced to reinstall the old antenna. I can not think of what else would be causing this very annoying problem.......

 

[ridgescan]

I thought discones were unity gain?
How about switching back to a "weaker antenna" maybe experiment that way to see if it is overload?
Also, did you put up that discone AND you're still running the original antenna off one scanner too?
prcguy-could there be some sort of "phasing" going on even with just a receive situation?

 

[RANGERDALEXP]

I thought discones were unity gain?
How about switching back to a "weaker antenna" maybe experiment that way to see if it is overload?
Also, did you put up that discone AND you're still running the original antenna off one scanner too?
prcguy-could there be some sort of "phasing" going on even with just a receive situation?

It is one antenna and two scanners through a SP1300. With SP1300 removed and direct to the one scanner there is no change in the problem. The problem started several days later. If it was a overload in the signal, then I would think the attenuator would make a change but it does not.....

Switching back to the weaker antenna would trash can the whole purpose of why I purchased the second radio....

 

[prcguy]

It doesn't sound like your problem is from a broken or defective antenna and I doubt a coax problem, shorted or open would cause the distortion you describe. It sounds more like a multipath problem to me.

I think your on the right track in making a change, checking the results and changing something else if no improvement is found. By process of elimination you'll eventually find it.

I would change simple things that don't cost any money first like swapping to your old antenna and try with the current coax, etc.
prcguy

I want to say thank you prcguy for being the only one to try to help with this problem. I thought more people would have more input or ideas but I guess not. even though the problem is not fixed I have come up with a strategy that I will do sometime next week. I am going to replace all the cable with new beldon cable. If that does not fix the problem I will then be forced to reinstall the old antenna. I can not think of what else would be causing this very annoying problem.......

 

[Dewey]

Although the problem seemed to "slowly" appear, I still would not rule out desensing/overload/intermod right away... especially, given the fact that the same problem is appearing when the splitter is removed. A good cheap and lazy man's indicator... **me**, would be to first run one of the scanners off of a back of set antenna. If the signal does anything other than get worse, I would take it as a good sign that either I have a defective antenna install or desensing/overload/intermod going on. From there, I would probably dig out the continuity meter and start checking for continuity between both ground ends and center ends of then coax, then shorting across the ground and center ends. Finally, if you did something like buy a 50' roll of coax and only use say 10' feet while the other 40' lay coiled up somewhere, you could be losing signal due to coax length.

Dewey

 

[LtDoc]

Along with the other things mentioned, a 'gradual' decrease in performance is sort of typical for an intermittent or 'bad' connection somewhere (corrosion, oxidation, birds 'pooping' on something?). I agree, check the 'easy'/non-expensive things first!
- 'Doc

 

[RANGERDALEXP]

I hope it is not a multi path problem because I can not move the house. I am hoping it is just a connection problem. If it is a multi path problem what is the fix for it other then moving the antenna to another city? If I have to scrap the discone antenna and go with another one what would be the best wide band antenna to go with?

I won't be able to do much with this till next week but I would consider changing the antenna if none of the test goes well. What I was running was a Radio shack wide band mobile antenna on the pipe mast before switching to the discone antenna.

As for checking with another scanner, I have one set up in our toy hauler that is 20 feet from the house antenna on a separate set up using the same style RS mobile antenna and there is no distortion on that set up, That radio is a RS Pro 2004 which was my old radio.

As for the RS RG 58 I had bought, I was a little disappointed with the shield it came with compared to the piece of old RS cable from 20 years ago that was still attached to the discone, the new stuff did not look as good of quality as the older stuff. What is the max length of cable that can be used on a scanner anyways? I am around 60 to 70 feet and I can not make it shorter due to the way it takes for the wire run.....

 

[Dewey]

...
As for the RS RG 58 I had bought, I was a little disappointed with the shield it came with compared to the piece of old RS cable from 20 years ago that was still attached to the discone, the new stuff did not look as good of quality as the older stuff. What is the max length of cable that can be used on a scanner anyways? I am around 60 to 70 feet and I can not make it shorter due to the way it takes for the wire run.....

60 -70 feet is a L - O - N - G W - A - Y for RG 58. At a minimum, I would go with a RG-6 quad shield.

Dewey

 

[RANGERDALEXP]

60 -70 feet is a L - O - N - G W - A - Y for RG 58. At a minimum, I would go with a RG-6 quad shield.

Dewey

Are you sure that RG 6 is the way to go on this? It is not 50 ohm but 75 ohm used for CCTV or cable TV? If this is the case I have thousands of feet of that stuff around. Would this be the best way to go?...

I have also thousands of feet of RG59 which is 75 ohm as well. will 75 ohm be a problem on a single antenna install. I know that they use it on installs on duel antennas with CB equipment....

 

[ridgescan]

60 -70 feet is a L - O - N - G W - A - Y for RG 58. At a minimum, I would go with a RG-6 quad shield.

Dewey

Quad shield=good stuff for scanning! Or-I paid $75 at HRO for 100' of lmr240 and it is great stuff! Solid copper lead, foil wrap outer, tinned copper 95% braid, outdoor/buryable jacket-and it's only a little bit thicker than that rg58 so easy to maneuver. Definately upgrade your coax first

 

[W6KRU]

Are you sure that RG 6 is the way to go on this? It is not 50 ohm but 75 ohm used for CCTV or cable TV? If this is the case I have thousands of feet of that stuff around. Would this be the best way to go?...

I have also thousands of feet of RG59 which is 75 ohm as well. will 75 ohm be a problem on a single antenna install. I know that they use it on installs on duel antennas with CB equipment....

RG-6 will be fine for your use. With a broadband application, the impedance varies greatly anyway.

 

[RANGERDALEXP]

I did some looking around on the Internet and it does look like good stuff as long as you do not transmit on it. I do a lot of cctv video work and have boxes of RG6 quad as well as RG59 around the house but was concerned about the impedance issue with using it. You guys say use it and I will do that next week...

 

[prcguy]

At VHF/UHF moving the antenna a few feet can change multipath characteristics.

I would use a good 50ohm cable like LMR400. Modern RG-6 has lower loss than say RG-58 or RG-8X (mini 8) but unless you get a bunch of RG-6 for free or don’t care about compromise just do the right thing and use 50ohm cable.

Also, RG-6 quad shield has no advantage for scanner reception use over single shield, its the same loss. Quad shield is used when cables are bundled together and leakage between cables is a concern. This is usually done for satellite cables with signals past 2GHz, at lower frequencies the leakage is much less of a concern.
prcguy

I hope it is not a multi path problem because I can not move the house. I am hoping it is just a connection problem. If it is a multi path problem what is the fix for it other then moving the antenna to another city? If I have to scrap the discone antenna and go with another one what would be the best wide band antenna to go with?

I won't be able to do much with this till next week but I would consider changing the antenna if none of the test goes well. What I was running was a Radio shack wide band mobile antenna on the pipe mast before switching to the discone antenna.

As for checking with another scanner, I have one set up in our toy hauler that is 20 feet from the house antenna on a separate set up using the same style RS mobile antenna and there is no distortion on that set up, That radio is a RS Pro 2004 which was my old radio.

As for the RS RG 58 I had bought, I was a little disappointed with the shield it came with compared to the piece of old RS cable from 20 years ago that was still attached to the discone, the new stuff did not look as good of quality as the older stuff. What is the max length of cable that can be used on a scanner anyways? I am around 60 to 70 feet and I can not make it shorter due to the way it takes for the wire run.....

 

[W2NJS]

I don't think that you will ever be able to solve this problem unless and until you break the system into parts and find out at what point the sensitivity goes, or begins to go, to hell. Electronic systems of any type with problems are fixed by "isolating and testing" and that's the way it's taught in service schools. I would also strongly recommend that if you intend to replace the coax that you get the best grade of low-loss 50-ohm cable you can afford and that you solder all of the plug connections, then test each connection with an ohmmeter for lack of continuity between the shield and the center conductor on each run. One of the best compromises on 50-ohm cable in runs of less than 100 feet is to use RG8X. RG8X with PL259 connectors uses the same reducing sleeve as the RG59 TV coax so it's easy to handle and, as I said, a good compromise for scanning setups due to its being cheap and of relatively low loss over shorter distances.

Your statement about how everything in the new setup worked okay for a while then got worse certainly sounds as if something that you disturbed during the reinstallation didn't get put back together quite right (I'm thinking "loose connection" here). I don't know if the splitter you're using is an active or passive unit. If it's active it could be producing noise, and if it's passive then it consists of a group of resistors designed to feed one signal to several outputs and there are any number of possibilities of this kind of device to go bad; it's not usual but it's possible.

 

[RANGERDALEXP]

From what I have read on this site and other sites is it does not matter on a receive only system if it is 50 ohm or 75 ohm cable? Also that RG 6 has a lower loss then RG 8 x or Mini 8 cable apparently. I have already concluded that it is not the splitter and I do not think it is the location due to the fact that this problem started days later and not at the time of the install. The new antenna is in the same exact location that the old one was and it did not have this problem for the last two years it was there. Also the other scanner and antenna is less then 20 feet from the new reinstall and does not have problems at all.

If I have to take everything down which is a major job to begin with and I have free RG 6 quad cable why should I buy LMR 400 at a $1.50 X 60 ft a foot if it is only a little better then the RG 6 quad. I have been a major CCTV/Access control systems integrator for 30 years and understand the process of troubleshooting electrical problems. As Dewey said and it makes sence, 70 feet is a long way on RG 58 and the stuff that is installed is CHEAP Rg 58 with what looks to be less then 60% sheild. I at this time think it is a bad connection so replacing the coax with a much better wire will eliminate the connection problem as well as poor wire....