[TowerTalk] Building K9YC Double Choke

Kirk Kleinschmidt sohosources at yahoo.com
Tue Dec 15 23:00:01 EST 2020

Hi, Jim and the gang,
The materials for my inverted-L choke FINALLY arrived (USPS delivery times weighed in at 13 days from Pro Audio Engineering to southern MN), and I'm preparing to build 2 14-turn chokes in series (FT-240-31 wound with parallel 12-gauge romex, per the choke cookbook), to give reasonable performance from 160-30 meters.
SPACING: I see in the choke book that W6GJB has a pair of RG-400 chokes in series, spaced about an inch apart on a length of PVC pipe. Is that sufficient for nomex chokes, or should the spacing be greater? If so, what's a good guess? 2 inches. 3 inches. Etc?
ENCLOSURE: I understand that TX chokes just wanna be out in the elements, but this choke needs to live in a crowded, insulated box at the base of the vertical, so I'd like some way to keep it somewhat self-contained. I was thinking about using a length of PVC pipe (3" ID) to house the chokes. End caps would provide mounts for the SO-239 connectors, and I'd cut the pipe in half length-wise so I can position the chokes and solder the wires to the chassis-mount connectors. When everything is good I can place the top "half" of the pipe in place and tape it together.
This choke will see max 100W (typically 5-10 W). Will the PVC negatively affect the romex choke's performance? If necessary, I could mount the chokes onto a smaller PVC pipe and attach metal brackets at the ends to mount the SO-239s...but that would make it more difficult to keep it separated from relays, tuners, connectors, temperature sensors, heating elements, etc. 

(Yes, LDG's RT-100 remote tuner stops working below 10F, so my base box is insulated and heated by a pair of power resistors mounted onto an aluminum heat sink which, in this case, is a heat source. MN winters always go below 10F. The RT-100 has performed well, but I consider the temperature limit a bit of a design fail, but it is what is is.)
If necessary I could mill long slits into the PVC pipe to ventilate it.
Thank you,
--Kirk, NT0Z  Rochester, MN  aka "the pest from the Midwest"

My book, "Stealth Amateur Radio," is now available from www.stealthamateur.com and on the Amazon Kindle (soon)

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