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Ree: QQDX and QMX+ (soon at least) what is the max safe swr?

 

I was thinking along those lines recently, how an awkward length
of coax feeder can cause high SWR on some bands.

Were such things available then a 2-pole 2-way coax switch
could be used to switch in-line an extra length of coax,
with perhaps several such things to switch in lengths of 1, 2, 4 and 8 foot lengths

On Sat, Sep 14, 2024 at 11:56 PM, Charles W. Powell wrote:
Sometimes the length of coax you are using will do this.? I recently
made a 49:1 for an end-fed half wave and installed the antenna.? I
couldn't get it to dip anywhere at all.? I checked the coax with an
analyzer and it was fine but the resonance was around 8 MHz.? I
substituted another shorter piece of coax and the antenna was spot on
for exactly what I expected.

Your mileage may vary, but the coax is the first thing I'd try.
 

Garth if that is true then the antenna is not presenting 50 ohms and the
SWR on the line exists.
?
However at some frequencies with antenna mismatch varying the
line length can alter the presented? impedance and SWR.
?
Example at exact halfwave (electrical) of the line the antenna
impedance will be seen at the source end.? At 1/4 wave electrical
(or 3/4, 5/4... odd quarter wave)? the antenna impedance will be
inverted...? A short would show as an open and an open as a short
for extreme cases.
?
The usual way for antenna designers to test for that is disconnect
the antenna end and? calibrate out the coax (using a VNA with
short, open, and load) then reconnecting the coax to the antenna.
At that point the coax reflections are canceled and the real antenna
impedance is measurable.
?
?
--
Allison
------------------
Post online only,?
direct email will go to a bit bucket.
 

I don¡¯t understand why there aren¡¯t and manufacturers that incorporate absorption bridges during the tune cycle for radio¡¯s¡­?
Good thing for the QMX+ proto-board.?
?

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