[TowerTalk] Radio Shack 300 Ohm Line Characteristics

[Bill Tippett]

At 01:16 PM 6/13/04, you wrote:
>Belden lists 22 AWG 300 ohm line as 1.4dB/100 ft at 100Mhz
>while stepping up to 20 gauge reduces loss to 1.1dB/100ft @
>100MHz. That's  the only data I have here in my catalogs.
>
>The rule of thumb for cables like this is at about 1/3 the
>frequency you should have about 1/2 the loss. So that would
>put Belden at .55dB loss per 100 ft at 33 MHz.
>
>It sounds like TLA is right on, based on what I see.

         Thanks Tom and several others.  The only specification
I can find is for Belden 8230 which uses 20 ga. 7 strands with pure
polyethylene (no foam).  Its loss numbers agree with your number
above and apparently the RS foam makes little difference.  So I'll
accept TLA's 300 ohm numbers as correct.  But TLA may actually
be understating losses for 450 ohm line. Page 6.9 of Wireman IV
shows #554 (14 Ga/19 strand) is 0.27 dB/100' at 30 MHz, instead
of the 0.146 dB/100' TLA assumes.  Wireman IV shows #551
(18 Ga/solid) is 0.37 dB/100' at 30 MHz and I can believe 300
ohm line could easily have  0.2dB higher loss.  The 0.4 dB
difference (nearly 4X higher) TLA shows between its 300 and 450
models was what I was having problems with.

         Since 10 and 15 meters will likely be poor for Field Day,
a few tenths of a dB will probably never be noticed anyway,
especially since I'll be QRP!  Thanks to all for the comments!

                                 73,  Bill  W4ZV

P.S.  Just read W4EF's note which I believe confirms that TLA
might be a little optimistic for 450 ohm windowed ladder line.