Core choice, wire length and winding style all play a part.
https://cromwell-intl.com/radio/9-1-unun/ and
https://g8jnj.webs.com/Balun%20construction.pdf
might help figure out what's happening.
Doesn't a coil in parallel with the 450ohms to cancel the tube's
capacitance mess things up at lower frequencies? What's the Cin?
Steve G8GSQ
A buddy is trying to get a 1:9 un-un to work on his grid driven tetrode.
Terminated in a 450 ohm globar, SWR is 1:1 but only up to aprx 20 mhz.
Above 20 mhz, it rapidly all goes to hell....reaching 2.5:1 at 29.00
mhz. ( this on the test bench)
He needs the 1:9 un-un to work from 80-10m. What's the trick here ?
What is the ideal material to wind the trifilar onto ?
Once eventually installed into the amp, a small coil is wired in parallel
with the 450 ohm globar to cancel out the XC from the tube, but that is a
normal procedure, and will not alleviate the high swr issue on the upper
bands.
Jim VE7RF
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