What if the outside temperature is already 95 to 100 degrees and then we start
heating up this RG-179 with the loss it has? So my question is is there
another
75 ohm coax that could be wrapped properly around some type of Mix 31 core as
well as having less loss and therefore less heat?
Maybe it isn't quite 10K ohms Rs on 160m or 13.5K Ohms Rs on 80m?
Maybe RG-302/U ?? Bending radius is 0.175" even though it has a solid center
conductor. Power handling is better than RG-179 and loss is a bit less. Total
diameter is 0.202" power handling listed at 1700 watts at 400 mhz.
On an FT-240 #31 core ID is 1.4" perhaps you could get to 17-18 turns on that
core. Yes that isn't 27 turns for 160m or 24 for 80m Perhaps two stacked FT-240
#31 cores would make the 10K Ohms numbers?
John k9uwa
Here are my recommendations for 75 ohm transmitting chokes wound with
FEP or PTFE mini-coax RG179 on 2.4-in o.d. #31 toroids. Turns are wound
close-spaced (touching on the inside diameter). As previously noted,
this coax has fairly high loss, so the choke should not see more than
the approximately 360W it would see when divided equally between four
verticals, and even at that power level, it MUST be exposed to air.
Note that I am NOT saying that they CAN handle this much power -- that's
up to others to verify.
160M: 27 turns 12K Ohms Rs
80M: 24 turns 13.5K Ohms Rs
40M: 22 turns 10K Ohms Rs
To develop these recommendations, I wound Grant's coax on the same four
cores at the limits of recently purchased cores used for my recent
RG400, THHN, and Teflon pair 2018 Cookbook, tabulated the data, and
chose worst case (lowest) values for Rs on each band.
73, Jim K9YC
John Goller, K9UWA & Jean Goller, N9PXF
Antique Radio Restorations
k9uwa@arrl.net
Visit our Web Site at:
http://www.JohnJeanAntiqueRadio.com
4836 Ranch Road
Leo, IN 46765
USA
1-260-637-6426
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