May 25th 11, 11:18 PM
posted to rec.radio.amateur.antenna
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First recorded activity by RadioBanter: Apr 2011
Posts: 60
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NVIS and VHF?
On 5/25/2011 5:17 PM, John KD5YI wrote:
On 5/25/2011 3:51 PM, Jim Lux wrote:
On 5/24/2011 5:17 PM, John KD5YI wrote:
On 5/24/2011 6:11 PM, Jim Lux wrote:
On 5/24/2011 2:54 PM, Dave Platt wrote:
I'm using 75' of
professionally assembled RG8X which is required to get from the
radio to
the antenna.
That's probably costing you about half of your power (assuming a
typical RG8X-type coax). Some lower-loss types (e.g. LMR-240 are
better than this.
The results are all over the map. A piece of Cable TV cable might
not be
a bad choice, if you can scrounge one. The 75 ohms probably isn't a big
deal.
At 144 MHz, bigger in diameter almost always beats fancier dielectric
(that is, the .405 inch RG-8, RG-213 flavors will usually beat any of
the quarter inch cables (RG-6, RG-8X, LMR240, etc.) because dielectric
losses aren't a big driver.. it's the IR loss in the center conductor.
RG-11, for instance, has less than 1.2dB loss for a matched 75 foot
line, and for the 1.5:1 mismatch, the loss only goes up 0.1 dB. (RG-11
type coax has a solid dielectric, and is pretty darn rugged stuff)
75 feet, at 144 MHz
LMR240 - 2.2 dB
Belden 8215 (RG-6A) - 2.5 dB
Belden 9258 (RG-8x) - 3.0 dB
Tandy RG-8x - 3.1 dB
Belden 8267 (RG-213) - 1.9 dB
Wireman CQ110 (RG-213) - 1.6 dB
Belden 8237 (RG-8) - 1.7 dB
belden 8213 (RG-11) = 1.2dB
Huh? 75 ft of RG-11 has almost 8dB of loss at 146MHz. 75 ft of LMR240
has 9.7dB of loss at 146 MHz.
I won't go through your entire list.
Check out http://www.vk1od.net/calc/tl/tllc.php
That's what I used..
Sure you got feet and not meters?
B9219, 75ft, 146 MHz = 1.811dB
Yes, Jim, Ralph pointed that out to me yesterday and I posted an apology
to him. I see that I should also analogize to you for my mistake.
^^^^^^^^^
Thanks to you both. Apologize
John
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