Posted by
k.igor on
Jan 03, 2011; 6:30am
URL: http://elecraft.85.s1.nabble.com/Curious-phenomenon-with-doublet-on-80m-tp5885101.html
Hello everybody,
Tonight I wanted to work station on 3504kHz but was not able to tune with K3
to transmit on that frequency. Here are the facts:
- The antenna is multi-band dipole, a.k.a Van Gorden or Doublet -
137ft dipole center fed with 450 Ohm ladder line.
- I do not use KAT3, it is installed but bypassed in this
configuration. I use MFJ-986 Differential-T tuner with built-in balun.
- I able to tune down to 1.1:1 on all frequencies above about 3505
with K3 and any other transceiver I tried. The optimal tuner settings at any
given frequency are the same for all transceivers (besides K3 I tried
Kenwood TS-930S and TS-570D with autotuner bypassed on both).
- My setting for tune power on K3 is 30W, on TS-570D - 30W, on
TS-930S - 50W
- On frequencies 3501 to 3505 with both Kenwood transceivers the
tuning is normal. With K3 the SWR is through the roof and there is no way I
can find resonance to see reasonable SWR.
- There is significant "hysteresis" to the phenomenon. When I move
down on frequency I am able to tune down to 3505 or so. When I see the
problem I have to return to about 3520 to see normal SWR again.
- The problem seem to be apparent only on this small part of the
band. I took time to go down from 3900 and was able to tune everywhere. Also
I didn't see any problem on low portion of 40m band.
Unfortunately, I don't have other antenna on 80m to compare. However, the
fact that I don't see any issues with the same setup with different
transceivers tells me that antenna and tuner probably are OK. I tried to
tune K3 with different power: from 10W to 50W - same behavior. I do not have
dummy load available at this moment, I will try tomorrow with dummy load.
Any thoughts?
73,
Igor, N1YX
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