ARRL

Forum Home - Rules - Help - Login - Forgot Password
Members can access, post and reply to the forums below. Before you do, please first read the RULES.

Need Help With Coax Choice

Nov 10th 2011, 13:18

AK4NX

Joined: Oct 26th 2011, 13:58
Total Topics: 0
Total Posts: 0
Hello,
Newbie to HAM, and my question concerns the correct choice of Coax cable. I'm going to run a 'stealth antenna' from my porch to an MFJ window pass-through a distance of no more than eighteen feet.
Then a piece three feet to my antenna tuner. Would I be better of with RG-58 or RG-8X coax? I'm going to purchase the length needed with PL-259s attached and understand they are already pre-measured.
Thanks,
John
AK4NX
Nov 10th 2011, 13:43

W1VT

Joined: Apr 4th 1998, 00:00
Total Topics: 0
Total Posts: 0

Hi John,

If you are using an antenna with a low SWR, like a 10M dipole cut to length, RG-58 will work just fine. But, if you want to use a tuner to operate the antenna on bands where there is a significant impedance mismatch, a lower loss cable can result in much better results on transmit. For instance, feeding a 10M dipole on 20M results in a whopping 20 dB of loss--going to RG-8X improves signals by 2dB. Going to low loss LMR-400/9913 improves signals by 6dB. One can do even better by hiding an automatic tuner next to the antenna feedpoint.

Zack Lau W1VT
ARRL Senior Lab Engineer
Nov 10th 2011, 16:19

AK4NX

Joined: Oct 26th 2011, 13:58
Total Topics: 0
Total Posts: 0
Hi Zack,
Thanks for the quick reply. Going to use an MFJ-1775 Multi-Band Rotatable Dipole, a Yaesu FC-902 Antenna Tuner, with a Yaesu FT-902DM transmitter. Using this combination of equipment which coax would you recommend for me?
John
AK4NX
Quote by W1VT

Hi John,

If you are using an antenna with a low SWR, like a 10M dipole cut to length, RG-58 will work just fine. But, if you want to use a tuner to operate the antenna on bands where there is a significant impedance mismatch, a lower loss cable can result in much better results on transmit. For instance, feeding a 10M dipole on 20M results in a whopping 20 dB of loss--going to RG-8X improves signals by 2dB. Going to low loss LMR-400/9913 improves signals by 6dB. One can do even better by hiding an automatic tuner next to the antenna feedpoint.

Zack Lau W1VT
ARRL Senior Lab Engineer
Jan 23rd 2012, 21:20

W2CSH

Joined: Apr 13th 1998, 00:00
Total Topics: 0
Total Posts: 0
I don't think it wil make any discernable difference over a 21 foot length of cable. Since at HF frequencies cable losses are generally specified over a 100 foot length I doubt if you could tell the difference even with a big missmatch. I use RG-8x for most everything. Its cheap and readily available. If you were running a long length then LMR-400 would be the ticket. Definitely worth the price for long runs.

Back to Top