Loss through coax?

[k1mri]

In the past week I've tried 4 antennas on my BCT15 with various results. I get the best reception with the antenna the scanner came with! Bear in mind I'm down in the basement and the coax is a 50ft. run of RG58 and the antennas are up in the attic 3 floors above.

Antenna 1 - is an old analog cell phone antenna that works well
Antenna 2 - a 2 meter mobile antanna that's dissapointing
Antenna 3 - is a new Diamond SW77CA, 2 meter portabe also dissapointing
Antenna 4 - is the one that came with the BCT15

The city I live in the local PD's repeater is about 1 mile from here at 50 watts output, yet with the first 3 antennas I'm only getting maybe a 2 in signal strength. I put on the Uniden antenna (directly mounted to the radio) and I get 4+ bars.

How much loss is there in coax or is it a combination of coax and antenna?

Thanks very much.

 

[PHOENIX_SCANNER]

RG58 @ 50' = Not much signal to the radio at higher frequencies. 800 / 900 mhz signals are pretty weak after 50' of that junk. Try LMR-400.

I don't know much about that scanner, but some scanners just don't handle the RF overload of an outdoor antenna well either, creating another set of issues, especially in the VHF Hi area. You may need attenuation in that area.

You COULD even have both issues, severe attenuation at really high frequencies, and not enough at VHF HI. Coax attenuation gets much worse the higher the frequency goes, and at a low enough frequency, it isn't even a factor really.

Either way, the proper outdoor antenna with the proper connectors and coax will almost always let you hear things you didn't hear before, and at the least hear things you already heard more clearly. Don't give up. Install better materials. To me LMR 400 is a minimum level of performance for 50' of coax.

Another thing. If you do not have proper grounding, and a good static discharge unit, nearby lightning strikes are going to send enough energy down into your radio to permanently damage the front end. Be sure you are protected. Even the wind rushing across a large enough antenna can lead to enough static buildup / discharge to damage equipment.

 

[af5rn]

It would help to know what band you are listening to. That makes all the difference, when it comes to antenna choice.

How are the first three antennas mounted? Do they have ground planes?

 

[Jakemcgraw]

In the past week I've tried 4 antennas on my BCT15 with various results. I get the best reception with the antenna the scanner came with! Bear in mind I'm down in the basement and the coax is a 50ft. run of RG58 and the antennas are up in the attic 3 floors above.

Antenna 1 - is an old analog cell phone antenna that works well
Antenna 2 - a 2 meter mobile antanna that's dissapointing
Antenna 3 - is a new Diamond SW77CA, 2 meter portabe also dissapointing
Antenna 4 - is the one that came with the BCT15

The city I live in the local PD's repeater is about 1 mile from here at 50 watts output, yet with the first 3 antennas I'm only getting maybe a 2 in signal strength. I put on the Uniden antenna (directly mounted to the radio) and I get 4+ bars.

How much loss is there in coax or is it a combination of coax and antenna?

Thanks very much.

I know its area and surroundings pending,, I had very good reception with the BCT-15 hooked up to a ST-2 scantenna, with 50 ft. of rg-6 commscope quadsheild coax.

 

[k1mri]

It would help to know what band you are listening to. That makes all the difference, when it comes to antenna choice.

How are the first three antennas mounted? Do they have ground planes?

I listen to 450~470 about 90% of the time
800 Trunked system 8% of the time

No ground planes. I was just trying out the antennas I have already. Like I said the Uniden supplied antenna works the best.

Thanks!

 

[Jakemcgraw]

When using the ST-2 scantenna on my BCT-15, i was monitoring the 46 mhz area, 155 - 162 mhz and 450-463 mhz freq. ranges with very good results...I can't speak for 800 mhz freq's as I don't monitor any.

 

[DPD1]

Even with poor quality coax you should be able to do better in the attic compared to an antenna on the radio in the basement. I would check and make sure there aren't any foil or other metallic materials over the roof or in the attic. Also, make sure that the connectors are properly affixed to the cable. Make sure you aren't getting a little piece of braid shorting it or anything. You can get a simple continuity tester for a few bucks at the hardware store.

Dave
www.DPDProductions.com
Antennas & Accessories for the RF Professional & Radio Hobbyist

 

[gmclam]

Outside antennas

Consider this; some antennas designed to cover a broad spectrum of frequencies for scanning (such as the discone) have ZERO gain. Now feed that signal down 50 feet of coax and you've got less signal. It amazes me how "picky" some people are about which (brand) scanner they use, but do not consider the importance of their antenna system. When I say antenna system I mean the actual antenna, the downlead (coax) and any other components or connections between the antenna and the receiver.

As you've learned the hard way, there's more to this than just putting up an antenna and running some coax you could easily find. The location you install your antenna is also important. The idea is that your antenna can "see" the transmitting antenna. At least don't install it behind something that definitely obstructs the signal. A little antenna height can do a lot for acquiring a better signal. But you do have to have good coax so that the extra length does not undo what the height gave you.

Get the best antenna for the job you can find. Get the best coax you can find. If you can't afford the best coax, don't even bother putting up the outside antenna. As you've learned the rubber duckie will likely do as good. Keep coax length to a reasonable minimum. Don't splice the coax or use "too many" connections.

EDIT: Here's a web site for calculating coax loss. There are several out there. Use the HIGHEST frequency you will be receiving (even if only 8%): http://www.ocarc.ca/coax.htm

Good luck

 

[kc2cjw]

Antennas and coax...

The biggest mistakes people make when running antennas are:
- Cheap Coax
- improper coax connector installaton
- wrong antenna.

If you're trying to listen to 800 Mhz, save 3 feet ofthe RG58 for a tail cable and get some Times LMR400, Belden 9913, or similar. At 800, 100 feet of RG58 will pretty much lose the signals you're looking for.

Get the *RIGHT* connectors for the cable purchased. Install them properly. Some may argue, but it is OK to make a "tail" cable of a few feet of RG58 to get from the 1/2-inch feed line up to the radio. In fact, it's better for the life of the radio if you DON'T have a couple of pounds of cable & connector tugging on its rear panel.

For GenPurp. scanning, the best antennas I've used are from the "Disc-cone" family. These are very broad in frequency coverage, Omni-directional, take little space, and are about $40.00 new. I have one at home and one on our local EMS HQ, and we pull in signals from 50 miles out on UHF-T, 100's of miles on VHF-Hi.

Ham antennas are designed to provide decent gain at specific frequencies, like 144-148 MHz. Out side of that, it could be quite deaf. A 5/8 wave antenna doesn't need a counterpoise ("Ground Plane"), but most antennas do.

Also, don't confuse "Ground Plane" for the RF signals with "Ground" for safety.

Good Luck.

 

[vortex360]

I took off 60ft of coax after seeing a chart on the signal loss and I was amazed at the results. I live in South Bend, Indiana and I am listening right now to Calumet City, Ill, Orland park, Ill, Tinley Park, Chicago, even the 800Mhz system out of the Illinois State Police. All of this is around a hundred miles away from me.

 

[af5rn]

No ground planes. I was just trying out the antennas I have already. Like I said the Uniden supplied antenna works the best.

There is the entire problem right there. That's like comparing four cars, but only putting wheels on one of them. The one with the wheels is going to win.

You have to use the antennas the way they were intended to be used, or they cannot perform. They have to have some sort of ground plane or the antenna is not complete, and you cannot evaluate their performance competently.

 

[gmclam]

6dB more

I ran some basic numbers at the link I posted earlier related to the OP's question.
Expect about 8dB of loss for 50 feet of RG-58.
Expect about 2dB of loss for 50 feet of LMR-400.
Loss will be less at lower frequencies, and it will be greater for more than 50 feet of coax. But just the selection of coax here and nothing more yields 6dB more signal!