[time-nuts] Lowloss cable?
Charles P. Steinmetz
charles_steinmetz at lavabit.com
Sun Jun 12 21:02:17 UTC 2011
Dick wrote:
>What's the best small diameter (<0.25") low loss coax?
How nuts do you want to get? You shouldn't need anything better than
a good RG-59 (75 ohms) for a 30' run. For that, I'd probably use
Belden 1426A if I were restricted to < 0.25". Good foam RG-6 (also
75 ohms) like Belden 1694A is better, if you can tolerate 7mm
diameter (.275"), but at 30' the difference in attenuation will be
less than 1 dB.
Note that GPS antenna manufacturers often specify (and supply) 75 ohm
RG-59 instead of 50 ohm RG-58, notwithstanding that the antennas and
GPS units are 50 ohms. This is because the effects from the
relatively small mismatch are more than outweighed by the typically 2
dB/100 ft. loss advantage of RG-59 over RG-58.
At 1 GHz, the losses per 100' of some candidates are:
1/4" Heliax: ~4.5 dB (~5 dB at 1.5 GHz)
Belden 1694A: ~6 dB (foam RG-6; 7mm diameter; some brands worse)
RG-401: ~7 dB (1/4" semi-rigid coax)
Belden 7808A: ~7.5 dB (low loss RG-8X; some others much worse)
LMR-240: ~8 dB (low loss RG-8X)
Aircell 7: ~8 dB (note: this is 7mm, a bit larger than 1/4")
Belden 1426A: ~8.5 (foam RG-59; some types/brands worse)
Aircell 5: ~9.4 dB (5mm OD)
Best regards,
Charles
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