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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

The definitive article on the Jpole was written by N3GO some years ago.

From a J to a Zepp
The truth and its consequences
Gary E. O'Neil, Raleigh, N.C. (N3GO)

73

-Jim
NU0C

On Sun, 19 Sep 2021 16:49:46 +0000 (UTC)
"KENT BRITAIN" <WA5VJB@...> wrote:

Terry Turner, W5ETG, now a silent Key, was the first to develop the twinlead J-Pole back in the 1960's.? ?That puppy has certainly traveled far!? ?The hard part today is finding Twinlead! hihi
On Sunday, September 19, 2021, 11:19:29 AM CDT, kk7xo via groups.io <kk7xo@...> wrote:

Thanks.? The reason I'm doing this is because I made a blog post about how to design a 2-meter twinlead J-Pole using SimSmith and the NanoVNA.? One of my readers asked me to post a final sweep of the SWR.? I have a sweep, but it is at the end of 15 feet of LMR-100 and I know it will look better than it really is, and I didn't want to cheat.
I will post the result in RL, and hope the reader can deal with that over SWR.? I think probably he can.
Just for fun I think I will sweep SWR with the calibration plane at the end of the coax and compare.

Albert KK7XO

I'm using a choke on the antenna feed. It may not be enough inductance, but it's better than nothing. Once I finish my blog post I'll put up a link in this thread. By the way, Roger, I'm using your component fixture to help with the design.

Thanks again! I missed that in your post... Thanks again!!

73, and thanks,
Dave (NK7Z)

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

On 9/19/21 10:00 AM, Dave (NK7Z) wrote:

Hi Jim,

THANK YOU!? I also have a Rig Expert AA-600.? If I sweep at the shack, I get a 2:1 bandwidth that is far wider, than if I sweep at the antenna feedpoint.

Why does the nano not show this same effect?? What am I missing?

Is it because the calibration the nano provides, removes the effects of the feedline, while the AA-600 does not, because it does not have a calibration option?

Sure, think about how putting, say, a 3dB pad would change the 2:1 bandwidth - it would make it wider, because it pushes the entire trace down 6dB.

You can see that on the plot I just posted - look at the resonance around 20 MHz, the blue trace (with coax) is wider at -14dB than the orange trace.