cable for antenna?

[Part15rulesdude]

signal loss can happen if you have too much cable from transmitter to antenna?
I think thats what happened to my part 15 fm, signal has decreased since I had to increase cable length!!!!!!! is it possible? HELP!!!!!

 

[tregonsee]

> signal loss can happen if you have too much cable from
> transmitter to antenna?
> I think thats what happened to my part 15 fm, signal has
> decreased since I had to increase cable length!!!!!!! is it
> possible? HELP!!!!!
>
Definitely possible at VHF.
1. What type of coax is original run - solid plastic center insulator or foam? Also, what designation (RG-58, RG-59, RG-8X, etc.)?
2. What type of coax is new run? If solid plastic, try foam, which generally has lower loss.
3. Can you put the xmtr closer to the antenna (in a weatherproof box if needed) and run power and audio to it? You may have to use shielded cable for the audio.

 

[Part15rulesdude]

> > signal loss can happen if you have too much cable from
> > transmitter to antenna?
> > I think thats what happened to my part 15 fm, signal has
> > decreased since I had to increase cable length!!!!!!! is
> it
> > possible? HELP!!!!!
> >
> Definitely possible at VHF.
> 1. What type of coax is original run - solid plastic center
> insulator or foam? Also, what designation (RG-58, RG-59,
> RG-8X, etc.)?
> 2. What type of coax is new run? If solid plastic, try
> foam, which generally has lower loss.
> 3. Can you put the xmtr closer to the antenna (in a
> weatherproof box if needed) and run power and audio to it?
> You may have to use shielded cable for the audio.
>
Its RG58 and no cant put trasmitter in weather proof box, and its the same kind of coax on both runs.........with a adapter in the middle to connect it...
So if thats the problem, would love to know.....

 

[easthill]

If you can afford it, use RG-8. It is a low loss cable and good for longer runs at VHF frequencies and low power levels. RG-8X is a good alternative if you can't use RG-8. Buy the best you can afford.

> Its RG58 and no cant put trasmitter in weather proof box,
> and its the same kind of coax on both runs.........with a
> adapter in the middle to connect it...
> So if thats the problem, would love to know.....
>
<P ID="signature">______________
Frank
East Hill Radio

Moderator, Community Radio USA, Seattle</P>

 

[Chuck]

> If you can afford it, use RG-8. It is a low loss cable and
> good for longer runs at VHF frequencies and low power
> levels. RG-8X is a good alternative if you can't use RG-8.
> Buy the best you can afford.
>
> > Its RG58 and no cant put trasmitter in weather proof box,
> > and its the same kind of coax on both runs.........with a
> > adapter in the middle to connect it...
> > So if thats the problem, would love to know.....
> >
>

If you are going to buy new cable, get Belden 9913. Accept no substitutes. Until you get into some very expensive 1/2" foam coax cable, it is probably your best choice. It's more or less RG-8 size, but lower loss. If I recall correctly (and I may not) it's less than 3db loss per 100 feet at 100 MHz. RG-58 has a lot more loss than that. ( I think it's about 10-12 db per 100 feet at 100 MHz, depending on manufacturer.)

You also mentioned that you have a connector mid-way. That's not a good idea. I don't know what type connector you are using, but some of those "splices" can cost you 2-3 db as well. Keep in mind that a 3 db loss means that your signal is half of what it was.

You also need to keep the feed line to your antenna as short as possible. If you are running a truly Part 15 compliant transmiter through 100 feet of RG-58, You will have little or no signal left by the time it gets to the antenna because of line loss.