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Even more interesting is to do a wide/multt-band sweep with the nanoVNA: You can easily see the effects of frequency on feedline losses in the loss.

I usually do a 1-30MHz sweep of my multiiband-HF antennas at both the feedpoint, and at the exciter (including any switches, transmatches, patch cables, etc).

-Mat, N8TW

On Sunday 19 September 2021 02:20:24 pm Roger Need via groups.io wrote:

On Sun, Sep 19, 2021 at 11:05 AM, <kk7xo@...> wrote:

By the way, that J-Pole article Jim posted is great. I'd like to link to it
from my article. Is it available online? Like maybe the ARRL site?

Albert KK7XO

Here you go >>>

Roger

Better, the pdf didn't include the figures...

--
Member of the toughest, meanest, deadliest, most unrelenting -- and
ablest -- form of life in this section of space, ?a critter that can
be killed but can't be tamed. ?--Robert A. Heinlein, "The Puppet Masters"
-
Information is more dangerous than cannon to a society ruled by lies. --James
M Dakin

Howdy Albert,
You can get SMA connectors for RG-8X (and -59, any .242" coax), tho you do of course need the ratchet crimper with the appropriate dies.. I got both on amazon a while back.
PL-259s are not that bad; the modern ones with Teflon are supposedly considerably better than the old phenolic ones. And the impedance bump is a small fraction of the wavelength at 2M.
Consider that most 2 meter mobile antennas are using 15-18 feet of RG-58 and a PL-259...
Also, consider that final tuning of the antenna is measured at the radio end of the coax; the object being to get 50 ohms at the radio.
73, --kv5r

Since the antenna is SMA, would it make sense to put BNC connectors on the RG-8x and use a BNC->SMA adapter? Then not only do you avoid the PL-259 entirely, but you can easily calibrate at the SMA.

If you have the strip and crimp tools, BNC crimp for RG-8x is easy, but even if you don't, BNC solder/clamp for RG-8x isn't rocket science.

73, Willie N1JBJ

If you calibrate at the end of the cable, there should be no difference in either case.
But I would choose option 1 because the attenuation of 18 feet of LMR-100 at 145MHz is only 1.62 dB and the performance of this cable will be normal. The performance of PL-259 connectors is difficult to predict. They usually have a lower impedance than 50 Ohms. I have such a PL259/SO239 connector set that has 25 Ohms. This increases the SWR to 1.3 on 145MHz and on 433 to 2.3.
I did an experiment once, I compared the results of antenna measurements on 433 connected directly, and using this bad PL259/SO239 25 Ohm set calibrating before the set and after the set. The calibration compensated for the error interjected by those connectors and the results were almost identical.
Green - direct connected antenna
Red - Antenna connected through wrong PL259/SO239 adapter set
Blue - Antenna connected through wrong PL259/SO239 adapter set, but calibrated after adapter set.

On Sun, Sep 19, 2021 at 11:33 AM, <kk7xo@...> wrote:

I have two pieces of coax I can use.

It's a bit late now for this reply, but here goes -

Do it with both cables, and compare the results.
Then you could share the results, too! I think it would be an interesting comparison.

--
Doug, K8RFT

The article by N3GO states
"I ran a quick ELNEC [3] simulation of an end-fed vertical dipole to assess what feedpoint impedance it predicted. I varied the wire size and height above ground to observe the changes, and the results appeared to vary slightly around 7000 ohms. "
I measured 6.12K – j2.54K which is close to his results.

The ZIP file also contains the HTML article and the figures that go along with it. Open JPOLE.HTM with your browser and you will see the article with the referenced figures.

73

-Jim
NU0C

On Sun, 19 Sep 2021 16:41:15 -0700
"Roger Need via groups.io" <sailtamarack@...> wrote:

On Sun, Sep 19, 2021 at 02:26 PM, Jim Shorney wrote:

I found a link to the full content of the article:

That appears to be just a link to a zip file containing the calculation programs. No article there from what I can see.

Roger

On Sun, Sep 19, 2021 at 02:26 PM, Jim Shorney wrote:

I found a link to the full content of the article:

That appears to be just a link to a zip file containing the calculation programs. No article there from what I can see.

Roger

I found a link to the full content of the article:



N3GO renewed his license in 2019 so presumably he is still around.

73

-Jim
NU0C


On Sun, 19 Sep 2021 11:20:24 -0700
"Roger Need via groups.io" <sailtamarack@...> wrote:

On Sun, Sep 19, 2021 at 11:05 AM, <kk7xo@...> wrote:

By the way, that J-Pole article Jim posted is great. I'd like to link to it
from my article. Is it available online? Like maybe the ARRL site?

Albert KK7XO

Here you go >>>

Roger

That's pretty much what I am seeing, although my feedline loss is 1.4 dB, giving a total of 2.8 dB up and backj.

On 9/19/21 11:47 AM, W0LEV wrote:

Jim reminds me that loss matching and loss broadbanding are both accepted
approaches in RF design. Of course the antenna is the worst place to
introduce losses in the system, but I've seen it used to broadband several
of the ionosonde LPDAs. In designing discrete "RF boxes", loss matching is
also excellent for stabilization between gain stages. And....these days,
gain is cheap.

No kidding, it is the core of the famous terminated folded dipole, especially the ones made of stainless steel cables.? If you're an embassy, or state operator, and you've got that 10 mW in to 10kW out amplifier from Harris, lossy broadbanding is a much better way to deal with things like ALE or frequency hopping than trying to run a tuner and wear out the relays.

Hams are somewhat unique in having a "output power" limit (as opposed to a radiated power or EIRP limit), but no requirement on efficiency, and, as well, various rules that tend to reduce the market for inexpensive amplifiers with 40dB of gain in one box.

Again, thanks for sharing!

73, and thanks,
Dave (NK7Z)

ARRL Volunteer Examiner
ARRL Technical Specialist, RFI
ARRL Asst. Director, NW Division, Technical Resources

Jim reminds me that loss matching and loss broadbanding are both accepted
approaches in RF design. Of course the antenna is the worst place to
introduce losses in the system, but I've seen it used to broadband several
of the ionosonde LPDAs. In designing discrete "RF boxes", loss matching is
also excellent for stabilization between gain stages. And....these days,
gain is cheap.

Dave - W?LEV

--
*Dave - W?LEV*
*Just Let Darwin Work*

On Sun, Sep 19, 2021 at 09:23 AM, Dave (NK7Z) wrote:

If you sweep with your calibration plane at the antenna, and at the VNA,
I would like to see those results...

73, and thanks,
Dave (NK7Z)

I posted both sweeps to my blog. A link to it is in another post I made to this thread. I don't know if it will be above or below this post because I don't know how groups.io orders these replies. :)

I don't think there would be a problem with hosting the PDF somewhere with proper source credit. I grabbed it off the net some years ago. The original web article is no longer up and the Internet Archive Wayback Machine is down at the moment due to internet outages so I don't know if it is archived there.

The moral of the story is if you see something useful to you save a copy of it. You can't depend on it being online next month, next year, or 20 years from now. :)

73

-Jim
NU0C


On Sun, 19 Sep 2021 11:20:24 -0700
"Roger Need via groups.io" <sailtamarack@...> wrote:

On Sun, Sep 19, 2021 at 11:05 AM, <kk7xo@...> wrote:

By the way, that J-Pole article Jim posted is great. I'd like to link to it
from my article. Is it available online? Like maybe the ARRL site?

Albert KK7XO

Here you go >>>

Roger

Attached are some plots for a antenna with nominal impedance 52 ohms at resonance of 10MHz, with zero and 1 dB loss in the feedline.

I chose the 52 ohms so that it wasn't a perfect match to 50 ohms so there's *some* mismatch (-30dB) at resonance

Great! Thanks, Roger. I added that to my reference section.

de KK7XO

On Sun, Sep 19, 2021 at 11:05 AM, <kk7xo@...> wrote:

By the way, that J-Pole article Jim posted is great. I'd like to link to it
from my article. Is it available online? Like maybe the ARRL site?

Albert KK7XO

Here you go >>>

Roger

Here is a link to my blog post:

By the way, that J-Pole article Jim posted is great. I'd like to link to it from my article. Is it available online? Like maybe the ARRL site?

Albert KK7XO