HF cable length

[ascott0172]

In general, how long of a run of RG-8 can one use for HF monitoring before loss becomes a concern? 100 feet? 200 feet? At what point would you want to think about using a preamp of some sort? Would another type of cable be better? My antenna site is going to be 150-200 feet from my shack give or take 50 feet and I'm wondering about signal loss. I could possibly move a bit closer but I'm trying to get as far as practical from noise from stuff in the house and power lines.

I'm going to be using an Alpha Delta DX Ultra antenna and most of my monitoring is utility type and amateur transmissions. Not that interested in sw broadcasting.

I realize there aren't any exact answers, I'm just looking for a rough guideline if that's possible.

 

[zz0468]

A couple of hundred feet of RG8 at 30 MHz or below will work just fine. It's about 1 db of loss per 100 feet at 30 MHz.

 

[prcguy]

HF signal to noise ratio is largely driven by high atmospheric and locally generated noise and below 15 or 20MHz you can have a lot of feedline loss and still retain the same SNR. If you were going for 10m groundwave reception you would want to minimize the loss.

A dipole used out of band (and maybe the antenna you are considering) can incur additional loss over the factory coax spec due to extreme antenna mismatch like operating at twice the frequency the dipole is cut for where the feedpoint impedance may be hundreds of ohms or more. In this case with 200ft of coax your signals could dip low enough to reduce the SNR.

To get around this you could simply put up the largest center fed dipole your property will allow and run TV twinlead or 450ohm balanced line to the receiver. This type of feedline is a terrible match to the antenna at most frequencies but the feedline loss is negligible compared to coax and the antenna "system" will be much happier.

I have lost count of hamsters who have had problems running multiple bands with simple dipoles fed with coax and when they switched to balanced line the antenna came alive and would tune everywhere. You can usually make an antenna for the fraction of what a commercial version would cost.
prcguy

 

[SCPD]

For strictly a non-commerical "monitoring" set up, you really don't need to worry about coax loss at HF frequencies. It's only a real concern when transmitting (and at higher frequencies.)

You didn't mention what kind of radio setup you have, but I would start with RG-213 coax. It's cheap but high-quality and readily available. You could invest in a higher-quality coax but it's really not worth the investment.

Coax Cable assemblies |RF 50 OHM| RFID Cables | Custom coax assemblies

You could also go with LMR-400 which is actually a bit cheaper but from my personal experience, RG-213 is a bit tougher and lasts longer.

Either would serve fine for your intended application.

 

[ascott0172]

Thanks for the info guys. I appreciate it.

 

[eorange]

I had the same question about a year ago, when I was planning a run of about 180 feet of RG8X to my vertical.

Bottom line: Rx and Tx loss is negligible from 80m to 10m. In addition to ham radio, I also use this setup to monitor utility comms. With everything else the same (radios, antenna), the performance definitely compares to my 80 foot run at my former QTH, which used better coax (RG-8).

For my 180 foot run - I bought RG8X/IIA from the RF Connection. It's Davis RF and seems to be high quality:

RF Connection Coaxial Cable

Hope this helps.

 

[N_Jay]

Remember, that in most cases if you don't have a good match to the cable, the cable will become part of the antenna.

This may be good (or bad) for reception