Antenna Woes!

[BillHolt555]

Help me if you can. I just installed a new Radio Shack Discone antenna outside my house.I have it at about 40 ft up on a metal pole. The problem I have is it will not recieve the local PD, which is only about 15 miles away. I can recieve them on my handheld with the rubber duckie inside my house, but when I connect the discone I cant. I have went thru the manual 3 times and I know I have it together as per instructions. Its bad when your handheld outpreforms your basestation. Any suggestions?
BillHolt555

 

[RayK]

You provide very little information: First what type and frequency is your local PD, Next what type of coax are you using ,its length ,type of connectors, lighting arrestor etc..
Before I install any outdoor antenna I would test it first with a short pole about 10 ft off the ground,so that its working ,next check the coax with a basic ohm meter , that you don't have a short from center pin to shield, next with the cable your using check continuity center pin to center pin,and shield to shield .

 

[ReceiverBeaver]

Yep, there must be something bad wrong. Also, a discone is a no-gain antenna to start with and you must have 50 feet or more of coax, the 40' up the mast and the extra length to get inside your house. All coax has losses so you have an antenna system that actually has some sort of negative gain figure.

Dump the discone and get a gain antenna. And you always need high quality low-loss coax for VHF & up.

 

[trainman111]

I would also agree to dump the discone especially if you're looking to listen to PD, FD and such. I have a discone but I use it for milair. I think it does a great job all around but I agree with ReceiverBeaver, get a gain antenna.

 

[kb2vxa]

After all the time and money invested you want him to dump it before he even knows what the problem is? You guys must have more money than brains.

Bill, just use a little common sense process of elimination before you eliminate the antenna. You might replace it only to find out the coax is bad when the new antenna doesn't work either. If nothing else you just learned something about antennas, don't put one up until you're sure everything is working.

 

[Don_Burke]

Any suggestions?

There are a couple of things I can think of right off.

- signal overload - I would hook an FM stereo receiver to the discone as a test. Those things are built for quite a bit of signal.

- bad coax or connector - Discones should read open with an ohmmeter.

- bad insulator on the antenna - The same ohmmeter should help figure that out.

- I never rule out an assembly mistake until I get an independent set of eyes to check my work.

 

[BillHolt555]

Antenna Woes

What type of gain antenna do you recommend? There is not much to chose from around here. Also I am using RG-58 Low Loss coaxial cable, from the neighborhood Radio Shack. 52 OHMS. I dont know any place else that sells this stuff locally anymore, like back in the CB days when you could get it at any store . Im only using 50 feet of coax. The mast is right outside my window. The frequencies im trying to monitor is 453.1250. I can recieve it ok on the stock antenna but not on this discone.
Thanx
Bill

 

[mancow]

Discones are fine as long as you recognize what their capability is.

I have one up around 30 feet. The difference is that I'm using Andrew miniature hardline. I am listening to a uhf frequency from 40 miles out right now.

As stated earlier, the problem is likely in the coax or connectors. RadioShack RG58 is piss poor. There's barely any shield braid in it at all. If you don't plan on transmitting then you will probably do fine with some RG6 type satellite TV coax.

Use the continuity meter or ohm meter and see if there are any shorts between the center and outer parts of the connector at your radio end first.

 

[Universaldecoder]

Does this type of antenna need grounding? Don't you need grounding of some sort?

 

[LordJ]

RG-58 coax is not really even a good idea for a 50' run or more...probably some loss issues there. Did you put on your own connectors? I would check there first. just grab the end that you have plugged in to the radio and check for continuity. Shouldn't be any between the center and the shield.

 

[Don_Burke]

What type of gain antenna do you recommend? There is not much to chose from around here. Also I am using RG-58 Low Loss coaxial cable, from the neighborhood Radio Shack. 52 OHMS. I dont know any place else that sells this stuff locally anymore, like back in the CB days when you could get it at any store . Im only using 50 feet of coax. The mast is right outside my window. The frequencies im trying to monitor is 453.1250. I can recieve it ok on the stock antenna but not on this discone.
Thanx
Bill

What you have should work for you once the bugs are knocked out.

I expect the coax will be okay until weathering makes you replace it anyway. That is unless you get hooked and want to pick up weaker signals, in which case all bets are off.

Once you get it up and running, start thinking about how to route RG-214 (or better) to that antenna.


I treat all claims of antenna gain with suspicion. Give the discone a fair trial.

Here is a little bit on selling antennas:
http://www.cebik.com/tales/sell.html

 

[Don_Burke]

Does this type of antenna need grounding? Don't you need grounding of some sort?

Not for picking up signals.

 

[ReceiverBeaver]

As others have mentioned, RG58 is about the worst coax you could have selected for this application. Did it really say "low loss" on the package? Well that's Radio shack for you.

You also said Bill that you don't have much available to you where you are. That may be true for local pickup but you're here talking to us on the internet. So you have the INTERNET. The whole world of shopping is at your fingertips and delivery to your door. Even if you don't use credit cards or like ordering online, you can still find stuff, contact businesses, obtain pricing, place an order and then mail them a check or money order to buy.

Many of us will gladly offer some antenna recommendations to you but you will need to tell us what frequency ranges you want to listen to.

Coax becomes increasingly lossy once you go above 100mhz. That RG58 was meant to use as mobile coax for CB radios which is down at 27mhz. It is wholly unsuitable for long runs of base station use at VHF and up frequencies.

Good luck and hang in there. Once you give us more information, we can fix you up.

 

[N_Jay]

. . Did it really say "low loss" on the package? Well that's Radio shack for you. . .

Yes it does, BECAUSE it is foam cable as opposed to standard RG-58 with solid dielectric.

Sometimes it helps to know before you comment. :lol:

 

[k9rzz]

If you can get at the antenna fairly easily, then take it down and hook it up to your radio with a very short piece of coax that you know is good. Then try to diagnose from there.

John K9RZZ

 

[trainman111]

And make sure you check those connectors! I put up my discone for milair a couple weeks ago, and after I hooked it up, I found that I had some continuity issues so I had to take all the connectors apart and redo them. The antenna works like a charm now. Good luck. With all the suggestions these guys have given, I'm sure you'll find the problem.

Nick

 

[BillHolt555]

Antenna Woes

Ok guys, Here is a list of frequencies I am trying to monitor. 460.1750, 453.1250, 453.6625, 452.7750, 460.4500, 460.5000. What would you guys recommend as far as a base antenna? I live in Tennessee so it is very hilly terrane. The discone that I have is not doing a very good job on some of these frequencies. I installed new coax today and it helped a little. (RG/6. I am not beyond buying new coax also, If you recommend it. I own 3 tow trucks and I want to stay on top of the police calls. Would a beam antenna work better than this discone? All of the Police Calls will be coming from about the same direction for me.
Thanx
Bill

 

[bwhite]

Take a look at this post, I think there is some good advice there for discones or any other type.
http://www.radioreference.com/forums/showthread.php?t=33859&highlight=ground

 

[mancow]

seems it would be more accurate for them to say it's low weight than low loss

I stripped back a piece of RadioShack RG58 once and there was almost no braid in there at all. There were just a few strands that weren't even tightly woven together.

Yes it does, BECAUSE it is foam cable as opposed to standard RG-58 with solid dielectric.

Sometimes it helps to know before you comment. :lol:

 

[Don_Burke]

Ok guys, Here is a list of frequencies I am trying to monitor. 460.1750, 453.1250, 453.6625, 452.7750, 460.4500, 460.5000. What would you guys recommend as far as a base antenna? I live in Tennessee so it is very hilly terrane. The discone that I have is not doing a very good job on some of these frequencies. I installed new coax today and it helped a little. (RG/6. I am not beyond buying new coax also, If you recommend it. I own 3 tow trucks and I want to stay on top of the police calls. Would a beam antenna work better than this discone? All of the Police Calls will be coming from about the same direction for me.
Thanx
Bill

If everything is coming from the same general direction, a beam will almost certainly do you some good.

With a pretty narrow range of frequencies, there are better choices than a discone in any case. Building an antenna would be my first option, probably a coaxial antenna or a j-pole.

Here is some information on a coaxial antenna:
http://emcesd.com/tt2006/tt020106.htm
http://www.pentodepress.com/receiving/patents/2184729.pdf

Later on, there are single frequency antennas with substantial gain:
http://www.rason.org/Projects/collant/collant.htm
That one is a real project to build.

Here is some information on a j-pole:
http://www.hamuniverse.com/jpole.html
http://ka1fsb.home.att.net/jpole.html

In hilly terrain, the real cure is height, which also means even better coax.