Tony,
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
On 2/18/2019 1:15 PM, Jim Brown wrote:
On 2/18/2019 11:40 AM, tony.kaz@verizon.net wrote:
Thanks for the input. I use dumped power to check the bandwidth.
Okay, will
use RG400 for the chokes.
That's 50 ohm coax, so not ideal for your application. KZ1W sent me
some miniature TFE coax to measure, the size of RG179, which is 75
ohms with FEP jacket. That would be a better choice. Because it's so
small (0.1-in o.d.), dissipation is fairly high, so it will be
important that it be exposed to air. I'm currently developing winding
guidelines for it. Because it's so much smaller than RG400, they are
very different.
_______________________________________________
RFI mailing list
RFI@contesting.com
http://lists.contesting.com/mailman/listinfo/rfi
|