You can match/measure the feed point of your antenna by using an _electrical_ half wavelength or multiples thereof, between the tuner/analyzer and the antenna.
Larry, K4MLA
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On 8/16/2020 2:39 PM, KENT BRITAIN wrote:
The wire may be non-resonate without your home brew matching network,but with the network it has to be.??? To be an efficient radiator, you haveto resonate.???? Kent WA5VJB
On Sunday, August 16, 2020, 1:34:08 PM CDT, David Eckhardt <davearea51a@...> wrote:
How many hams actually match *at the feedpoint* to a 50-ohm coaxial line?
I'll bet very few.? At VHF and UHF, yes, at the antenna match is practical
and usually accomplished, but not at HF.
That's why I use open wire feeders where SWR losses are *far* less than in
coaxial cable and the feedline is not stressed even with SWR at full
power.? And......I use a single set of wires for 630 through 6-meters with
that system with home brew matching network.
Antennas do not require being resonant to do a good job of radiating.? My
system is not resonant (¡À jX = 0.00, the definition of resonance) in any of
the HF ham bands, but it does very well, both in practice and in the 4NEC2
model.? It's lowest 1/2-wavelength resonant frequency is 950 kHz, the lower
1/3 of the AM BC band.? I seriously doubt I'd do any better with resonant
dipoles for all the individual bands.
Dave - W?LEV
On Sun, Aug 16, 2020 at 6:07 PM Chris Wilson <chris@...> wrote:
Hello David,
? Sunday, August 16, 2020
? Without? knowing what impedance the antenna itself presents, how do I
? know the best way to match it to the coax impedance?
Best regards,
? Chris? ? ? mailto:chris@...
DE> What's important is the load the antenna plus feedline present to our
DE> modern transceivers.? So, why the concern for 'at the antenna'
DE> measurements?? Sure, its nice to know, but the coax contributes it's
own
DE> impedance transforming properties.? If you must, make the measurement
at
DE> the shack end of the feedline, and use a tool such as SimSmith to take
out
DE> the impact of the coaxial line.
DE> Again, what is important is the load presented to the transmitter, not
DE> necessarily what the antenna impedance is at the feedpoint.? One must
STILL
DE> consider the transmission line between the transmitter and the antenna
DE> feedpoint to obtain this result.
DE> Dave - W?LEV
DE> On Sun, Aug 16, 2020 at 5:31 PM Jerry Gaffke via groups.io <jgaffke=
[email protected]>> wrote:
Roger wrote:
? You can clearly see that the two plots are nearly identical.
What kind of coax?
I bet it isn't RG174.
I have seen significant differences when checking out an HF antenna over
100 feet of RG8X.
I have a 20M dipole with a current balun attached to it which for this
test I consider to be the "feedpoint" of the antenna.
Not totally clear which side of the balun you consider to be the
feedpoint
of the antenna
I assume this means you leave the balun attached to the antenna, and
only
calibrate out the coax.
Jerry, KE7ER
On Sun, Aug 16, 2020 at 09:47 AM, Roger Need wrote:
I have a 20M dipole with a current balun attached to it which for this
test I
consider to be the "feedpoint" of the antenna. 55 feet of coax runs
back
to
the shack. First measurement with NanoVNA Saver was made at the
feedpoint and
stored as an s1p file. The coax was then "calibrated out" and a second
Saver
measurement made back in the shack. The first s1p file was then loaded
and a
comparison was made. You can clearly see that the two plots are nearly
identical.
Roger
