By total accident, the Icom R20 handheld helped me tune the chokes !!
It is one thing to see a change on the antenna analyzer when the chokes are attached at the 1/4 wave length down the coax. But what about something in the real world, that I can see?
To make a long story short, the RS #273-105 snap-ons definitely work at 127 mhz!
Initially I planned to use the R20's s-meter to do some adjustments on my standard weak test-signal - an atis station that I can make go away by merely looking at the antenna.
Using the S-meter didn't pan out, so I just put the antenna back on the Pro-136 desktop. Then I placed the whip back on the R20 (which is 23" long - a nice quarter-wave for aircraft) and put only one choke back on the coax. When I accidentally swung the whip near the base of the antenna - it made the atis signal totally drop out. Take the choke off, and I can NOT detune the bottom element and the atis signal returns weakly.
Ok, looks like this resonant whip of the R20 was detuning what was a 1/4 wave wire in the making on the coax antenna. Here it comes:
With only one choke installed, I could detune the coax antenna by holding the whip parallel about 3 inches away from the bottom element.
With 2 chokes, detuning took place about 9 inches away.
With 3 chokes, detuned at about 14 inches away.
With 4 chokes, detuning was at about 18 inches away!!
Then I ran out of the 273-105 chokes.
Unbelievable - something is working! It didn't improve my weak atis signal that much really, but I'm glad nobody saw me sitting on the floor waving that whip around like a crazed orchestra conductor.
I also tested some of my other chokes, like 4 to 6 #273-069's, and they didn't perform nearly as well. So for me, I'm going to stick with the 273-105's. I believe they might be "type 43" ferrite material, so I may go looking for cheaper alternatives.
Nice to see the choking action actually working by accident. Next best thing to lobe-spray.