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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 9/19/21 9:23 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)

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

Here's an example of a 6BTV with 100 ft of RG-8X.

Blue trace is cal at the NanoVNA

Orange trace is cal at the end of the Coax.

You can pretty clearly see the loss of the coax increasing with frequency.

Also attached is a plot of the measurement of two 100 ft cables, (new and old) with the cal at the NanoVNA end, and the far end of the coax just open.

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)

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

SO-239 are not so bad at VHF, and in theory the affect generated by the connectors, in general, is equal across a broad frequency range. If you are within that range, then the connector type is not an issue. In general, as with everything, there are examples where this fails, but not many...

Same for Coax... As long as you are within the design frequency range the cable, the issues caused, are generally the same across various frequencies.

You will see different loss figures for cables, but across most ham bands, the losses are close to equal, across a narrow frequency range. That is to say, if you loose 1 db at 144 MHz., you will probably loose close to 1 db at 145 MHz. Again, as with everything, there are exceptions. As a rule though, if you are within the design specs of the cable and connector, you can just use them as if they are interchangeable, RG-8, LMR400, RG-8x, etc.

Even if you were on an a design edge, and you had slight to medium differences between the lower end of 2 meters, and the upper end of 2 meters, (loss wise), the calibration process would fix this, assuming you calibrated using the antenna end of the coax as your reference plane....

The nanoVNA is a wonderful device!!

73, and thanks,
Dave (NK7Z)

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

On 9/19/21 9:12 AM, KENT BRITAIN wrote:

You loose a few dB of dynamic range, but since a 20 dB RL is the same as a 1.1 to 1 SWR,I'm sure you have plenty of dynamic range! hihi? ?And now you know why so many of us like to work in Return Loss vs then R's.? Kent WA5VJB

I think |S11| = -20dB is more like 1:1.22 VSWR

1:1.1 is 26 dB

1:1.5 is 14 dB

1:2 is 10 dB

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

Yes, you will lose a bit of dynamic range. However, consider the "raw"
dynamic range of the NANOs. At 2-meters, you have more than enough dynamic
range in the instrument to throw away a bit.

Actually, neither coax is appropriate for VHF. The LMR-100 is lossy at
2-meters as is RG-8X. Neither is too good at 2-meters. Then throw in the
nasty SO-239 / PL-259 on the RG-8X. Use the LMR-100 and don't sweat the
small loss of dynamic range. .

Dave - W?LEV

On Sun, Sep 19, 2021 at 4:09 PM kk7xo via groups.io <kk7xo=
[email protected]> wrote:

That's interesting. I didn't think of using return loss instead of VSWR.
I was thinking my VSWR would be much improved at the end of a lossy cable
and I couldn't think of a way to correct for it. But return loss is the
way. Simple math actually.
But I wonder how calibrating at the end of the lossy coax will affect my
sweep. Do I lose dynamic range?
Albert

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

On 9/19/21 9:09 AM, kk7xo via groups.io wrote:

That's interesting. I didn't think of using return loss instead of VSWR. I was thinking my VSWR would be much improved at the end of a lossy cable and I couldn't think of a way to correct for it. But return loss is the way. Simple math actually.
But I wonder how calibrating at the end of the lossy coax will affect my sweep. Do I lose dynamic range?
Albert

You'll lose a little bit of dynamic range, but, really, how much do you need.? If your antenna has a |S11| of -20dB or -30dB, then the fact that the dynamic range is now 50dB instead of 60dB isn't going to be a big thing, is it?

TBH, if it's easy, I'd calibrate at the end of the coax - if nothing else, the impedances are not transformed by the transmission line.? Subtracting loss from RL doesn't account for the phase shift.? Just be careful if the coax changes loss when you move it, etc.

The other thing that can trouble you unexpectedly is that for a lot of antennas, the coax is part of the antenna system (either by design, or happenstance).

You loose a few dB of dynamic range, but since a 20 dB RL is the same as a 1.1 to 1 SWR,I'm sure you have plenty of dynamic range! hihi? ?And now you know why so many of us like to work in Return Loss vs then R's.? Kent WA5VJB

That's interesting. I didn't think of using return loss instead of VSWR. I was thinking my VSWR would be much improved at the end of a lossy cable and I couldn't think of a way to correct for it. But return loss is the way. Simple math actually.
But I wonder how calibrating at the end of the lossy coax will affect my sweep. Do I lose dynamic range?
Albert

Hi Albert
You can cal at the end of the coax, but you don't have to.
Lets say the coax has about 2 dB of loss.2 dB of the signal is lost going up, and 2 dBis lost coming back down.Thus the antenna is 4 dB worse than you though it was.
In dB a measured Return Loss of 20 dB RL was really 16 dB RL.
In SWR ....... the math takes a while! hihi.? ? ??
In either case, you are making sure the antenna is on frequency, the coax shouldn't change that.?(Yes, I know a few exceptions)? and if you adjust the antenna for best RL/SWR, then you have adjusted the antenna for best RL/SWR.? It's as good as you are going to get!
Good luck with your project.? ?Kent WA5VJB? ?Antenna Editor CQ Magazine

I had the same problem, which appears when making the calibration and SHORT probe does no electric contact is made with the CH0 connector.
Solving was by tightening the warm wire in the CH0 connector.

I want to sweep my 2 meter antenna from the end of a 15 to 18 foot coax. This is because I need to get the antenna out in the clear away from nearby objects to get a good indication of the actual VSWR. The antenna has an SMA connector. I have two pieces of coax I can use. One is 15' of LMR-100 with SMA connectors on both ends. The other is an 18' piece of RG-8X with PL-259 connectors at both ends. In either case I can move the plane of calibration to the end of the coax where the antenna connects.
So I have two questions for those who have a lot of VNA experience in this group:
1) Since LMR-100 is lossy at 2m frequencies, will I lose much precision in the sweep by calibrating at the end of the coax?
2) Am I better off using RG-8X knowing that I will need to adapt the PL-259 to SMA at both ends? I understand that PL-259 connectors are not so good at VHF and adding adapters will only make them worse.
Which is the better alternative?

Albert KK7XO

On 19/09/2021 12:56, DougVL wrote:

FYI, when you're looking at your own posting, underneath are 3 links that say
Reply Like More
If you click on the "More" link, you can choose to edit your post (and correct typing mistakes). I have had to do that a few times.
-- Doug, K8RFT

Although as an e-mail subscriber it can be frustrating to see a whole string of messages all but one of which say "Edited message" (or whatever it is). Of course, it's a very useful feature at times, but I would rather folk review their message /before/ posting rather than after!

(I'm as guilty as anyone at making mistakes, of course!)

73,
David GM8ARV
--
SatSignal Software - Quality software for you
Web:
Email: david-taylor@...
Twitter: @gm8arv

FYI, when you're looking at your own posting, underneath are 3 links that say

Reply Like More

If you click on the "More" link, you can choose to edit your post (and correct typing mistakes). I have had to do that a few times.
--
Doug, K8RFT

Buy, I meant *buy* an original Hugen NanoVNA!

Update. I did return the non Hugen "NanoVNA". Call them fakes, counterfeit, clones or what you will. The clone's branding and packaging is clearly intended to deceive the purchaser.
I have now received a genuine unit with the correct QR code and the specified mcu. I now realise how poor the copy was, the fit of the case, lower quality switches, screen, out of date firmware and some unmarked components of dubious origin.
Do the right thing and yourself a favour. But an original, real product.

I think these RF test boards help, trains you on results, if you have set the vnanano up and calibrated correctly, getting the prescribed results gives us ou some confidence in the nano.

Interestingly, inside KEIL, STM32F302CB and STM32F302CC use the same memory description file. So in fact STM32F302CB and STM32F302CC may use the same Die, just marked as different models when packaging. You can try to refresh the latest firmware, then save the calibration data to SAVE6, then Recall 6, if the data can be recalled normally, then STM32F302CB and STM32F302CC have the same flash.

A cheap LCR meter is also a good option for measuring variable capacitors.
The value of most types of capacitors does not vary wildly with measurement
frequency. The value of inductors does, which is why the LCR meter is not
always a good option for measuring them.

On Thu, Sep 16, 2021 at 1:43 PM Roger Need via groups.io <sailtamarack=
[email protected]> wrote:

I did some measurements on a variable capacitor in my junkbox. It was
from an old MW receiver.

I measured the closed position on a calibrated DE-5000 LCR meter and it
was 367 pF.
In the open position it measured 8.5 pF

I set my NanoVNA-H4 to a stimulus range of 1 to 10 MHz. I used a RG-58
cable with alligator clips on the end. This type of test jig is OK at
lower HF frequencies but stray capacitance/inductance affects the results
as you go much higher.

A SOL Calibration was done using the alligator clips and a 50 ohm carbon
resistor (non inductive). When connecting the alligator clips to the
variable capacitor make sure the ground alligator clip goes to the frame of
the variable capacitor.

The NanoVNA gets the most accurate reading when |Z| is 50 ohms. In the
fully closed position the capacitor measured 365 pF when the magnitude of Z
was 50 ohms (bottom of Smith Chart). Only 2 pF difference compared to the
DE-5000. Connecting the the NanoVNA to a PC and using the NanoVNA app the
measured capacitance from 1 to 10 MHz was plotted. The measured
capacitance ranged from 371 pF to 363 pF which is quite close.

Next the variable capacitor was set to the open position. It is not
possible to measure at |Z| = 50 ohms because this occurs around 375 MHz..
However the NanoVNA-H4 still gives a reasonable estimate ranging from 8 to
8.3 pF over the 1 to 10 MHz. range which is close to the 8.5 pF measured on
the LCR meter.

Experimental results are attached.

Roger