0
$\begingroup$

I have room to erect a DX Commander, multi-band vertical, and to give it a good number of radials on a good clear site.

Problem is I would need to run about 80 - 100m of coax feed from operating position. Is this too long?

Planning on 25W SSB and CW on 80,40,20 and 10m

$\endgroup$
6
  • 2
    $\begingroup$ From the top of my head, RG-6/U has something like 20 dB attenuation at 100 MHz, and for closer-to-DC frequencies like like 4 MHz (80 m band, if I remember correctly? I'm still not used to specifying things in free-space wavelengths – that's a bit awkward in systems where waves travel in media) less than 2 dB. You'll be fine – for reception anyways, and for TX, you will need to gauge how much cable investment you want to do to avoid TX power loss. But that's honestly down to your budget and your needs! $\endgroup$ Feb 10, 2023 at 12:36
  • 2
    $\begingroup$ If you want to know whether a prospective feedline is "too long", first define how much signal loss is "too much" and how much cost is "too expensive". $\endgroup$ Feb 10, 2023 at 12:43
  • $\begingroup$ Fair comment @hobbs - KC2G 3dB loss would be OK, less than 50USD 40GBP would be nice $\endgroup$ Feb 10, 2023 at 13:32
  • 2
    $\begingroup$ @MarcusMüller The loss vs. frequency curves for RG-6 and RG-213 are quite similar. $\endgroup$ Feb 10, 2023 at 17:30
  • 1
    $\begingroup$ @quanglewangle for direct burial (or any outdoor use really) try to find gel-filled cable - the braid makes an excellent wick for water, so the smallest nick in the jacket will soon ruin the whole cable. In outdoor cable they impregnate the braid with a gel, so there's no space for water. (You can get 1000' of outdoor gel-filled RG-6 for just over $100) $\endgroup$
    – tomnexus
    Feb 11, 2023 at 8:03

1 Answer 1

4
$\begingroup$

With a 100m feedline, your loss target is not too hard to meet — RG-8 has a loss of about 2.5dB per 100m at 30MHz (lower at lower frequencies).

You'll have to compromise on the cost target, though. I don't know much about UK prices, but here in the US, RG-8 currently goes for about \$0.90/foot in bulk, so right around \$300 for 100m of it, not including connectors. Shooting for under \$100 puts you in the range of RG-58, which has a loss of around 8.5dB/100m at 30MHz, and 6dB/100m at 15MHz, which is less fun. $50 won't even get you that.

$\endgroup$
4
  • $\begingroup$ Very helpful. Can get 300ft for about 190USD, overnight Unfortunately in 100ft rolls so will need to step up to waterproof joints. $\endgroup$ Feb 10, 2023 at 17:02
  • 1
    $\begingroup$ Rather than making joints, fit connectors to each piece, bring the ends up under a waterproof roof like a metal bowl or something (open at the bottom) and join them with a barrel. That way you don't have to trust the glue/tape, and if one cable gets wet and is damaged the others won't be affected. $\endgroup$
    – tomnexus
    Feb 11, 2023 at 8:06
  • 1
    $\begingroup$ 2.5 db loss turns the 25W produced into 14W-16W before the antenna. $\endgroup$
    – user23328
    Feb 25, 2023 at 4:47
  • $\begingroup$ RG-8 is a generalization of a class of 1/2 inch coax, and is quite ambiguous in its varieties: Mini, U, A, There are major differences in loss. Please be more specific in your answer. A 1/4 inch Andrews/Comscope hardline offers a similar loss factor, higher power capabilities and a 100% instulation factor for pennies more. Not to mention the 1/2 and 3/4 inch varieties almost no loss at 50 MHz at 100M. A one time investment. $\endgroup$
    – user23328
    Feb 25, 2023 at 4:48

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .