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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.

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 (± 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

Does anyone have a suggestion for a soft, clamshell style, padded storage case
that'll fit a NanoVNA-H4 with enough extra room for typical accessories?

I’ve searched for hours and so far come up empty handed...

Does anyone have a suggestion for a soft, clamshell style, padded storage case that'll fit a NanoVNA-H4 with enough extra room for typical accessories? It needs to have a separate inner zippered compartment to store the calibration fittings and coax jumpers so they won’t rattle around and rub on the NanoVNA's screen.

I've seen multimeter storage cases which are close, but they're either way too big or lack a zippered internal storage compartment. A portable hard drive case might work also, but again, every one I've encountered lacks an internal zippered storage compartment.

Ideally being able to buy from Amazon or eBay would be best.

Thanks in advance,

John
AA7US

We should clarify something here regarding very short (as a function of
free space wavelength) radiators.

A short radiator (a short monopole or small open ended 'wires' of a
transmission line) exhibits an extremely *low real part *of the feed
impedance or radiation resistance (neglecting ohmic losses, for the time
being). The impedance is predominantly capacitive. It forms a capacitive
probe to free space and is typically a very inefficient radiator due to
resulting small currents whose fields (generated by those moving or
oscillating charge carriers) open onto free space. A large series inductor
is required to 'resonate' with this capacitance which boosts the generated
fields due to increased currents at resonance. Remember, resonance is
defined by the absence of the complex term in the feed or radiation
impedance. Most of the current in such a structure exists below the
inductor (loaded mobile whip) and on the structure to which the loaded
"antenna' is attached. What's left is the radiation resistance and the
ohmic resistance of the coil support and the wire of the inductor, itself.
Typically, the sum of the last two greatly exceeds the radiation resistance
- that which produces the energy radiated into free space - by a good
amount.

Small radiating structures exhibit a low real part and a large complex
(capacitive) portion of the feed impedance.

Dave - W?LEV

If, after calibration, there were perfect opens and shorts* at the
reference plane*, there would be dots. But the standards apply opens and
shorts some distance from the reference plane, so the arcs exist.

The delay on that female short is 27.99 ps. The delay on the male short is
significantly longer (63.078 ps), so had I shown the male, the arc would
have been more than twice the length.

Dave