**Ismo**2022/02/27 08:39

hi,

I have two cables (H155) 2mtr each. With Nanovna V2, how to make (measure) one of these to be 1/4 wave shorter in 435Mhz?

br ismo

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hi,

I have two cables (H155) 2mtr each. With Nanovna V2, how to make (measure) one of these to be 1/4 wave shorter in 435Mhz?

br ismo

Your question is not clear to me. Perhaps you can rephrase so it is more clear.

Are you asking how to use your NanoVNA v2 to measure the wavelength of an existing cable?

Are you asking how much cable to remove from each of your existing 2m H155 cables to make them each quarter wavelength long at 435MHz?

Are you asking how to calculate the length of wire to be 1/4-wavelength at 435MHz?

Are you asking how to make some specific modification to an existing RHCP antenna?

Other?

hi,

Thanks for your reply. As I wrote the second cable must be 1/4 wave x VF longer.

So if the first cable is 1,5mtr Aircell 7 (VF 0,85) second one must be that 1/4 x VF longer.

Antenna is Wimo X-Quad for 435Mhz.

My question is how to measure those cables with Nanovna v2 plus?

br ismo

On 28/02/2022 11:37, Michael Brun wrote:

> Your question is not clear to me. Perhaps you can rephrase so it is more clear.

>

> Are you asking how to use your NanoVNA v2 to measure the wavelength of an

> existing cable?

>

> Are you asking how much cable to remove from each of your existing 2m H155

> cables to make them each quarter wavelength long at 435MHz?

>

> Are you asking how to calculate the length of wire to be 1/4-wavelength at 435MHz?

>

> Are you asking how to make some specific modification to an existing RHCP antenna?

>

> Other?

Most likely was: "How to I make one cable an electrical quarter of a wavelength

longer than another?".

David

--

SatSignal Software - Quality software for you

Web: https://www.satsignal.eu

Email: david-taylor@blueyonder.co.uk

Twitter: @gm8arv

The most accurate method of measuring a 1/4 wave delay line is knowing that the impedance at the end of the transmission line repeats itself every 1/2 wavelength. Note the original line length and sweep, noting the frequencies where the fundamental and second harmonic null occurs (or peak, If the end is shorted). Snip off about 20 cm and carefully measure again for the new length. You can now precisely calculate the velocity factor of the feed line and wavelength for the desired frequency.

Step 1: Measure the electrical length of Line #1 using the NanoVNA - Calibrate, hook up the cable between CH0 and CH1, look at the phase of S21 at 435 MHz. Say it's 273 degrees - A wavelength at 435 is about 70cm in air, and roughly 50 cm in coax - so your coax is actually just under 4 wavelengths (for this example) - 360*3+273 =2080+273 = 1353 degrees.

Step 2: Calculate the length you need. You know that 2m is 1353 degrees, and you want your phasing line to be 1353-90 or 1263 degrees. Calculate 90 deg * 200cm/1353 deg - I get about 13cm. That's how much to cut off.

Step 3: cut off 13cm, install connector, remeasure

A trick - If you look at phase of the S11, with the far end unconnected, the phase is TWICE the length of the coax (i.e. in this case, it would read 186 degrees). Do the same calculation. Now, start cutting until the number is 180 degrees less.

The challenge is that you need to allow for the length of the connector in both techniques.

On 2/28/22 6:25 AM, N0YWB wrote:

> The most accurate method of measuring a 1/4 wave delay line is knowing

> that the impedance at the end of the transmission line repeats itself

> every 1/2 wavelength. Note the original line length and sweep, noting

> the frequencies where the fundamental and second harmonic null occurs

> (or peak, If the end is shorted). Snip off about 20 cm and carefully

> measure again for the new length. You can now precisely calculate the

> velocity factor of the feed line and wavelength for the desired

> frequency.

With a VNA, you can also measure S21 - and directly measure the

propagation speed.

Easiest way is to measure S21 as a Thru connection: measure phase at your operating frequency and compare the two phases

Note that for 70cm, 1/4 wavelength is about 15cm in your coax. An easy way might be to just get a 10-15 cm jumper and hook it in series and see what it reads.

(or, even more brute force, just stack N connector adapters.. A nice clean N doesn't have much of an impedance bump. An N F-F barrel is about 5 cm, so is a M-M.)

The other thing is "what is your tolerance requirement?" Do you care if it's 80 or 100 degrees instead of 90? If you have a connectorized cable (both ends) and you're comparing to a cable with a connector at only one end, you need to allow for the added length for the connector. That's hard to know, unless you've built them before, or if you figure that 10 degrees is about 1-2 cm, maybe you don't worry about it.

(It degrades the axial ratio slightly if you're looking for CP)

What *I* do when needing this kind of thing is get a single cable which is about 2x longer. Cut it roughly in the middle (maybe biased toward one side by your 15 cm).

Then, I hook up the shorter cable to the VNA and make an S11 measurement. Write down the phase of the S11.

Then, I hook up the longer cable, and start cutting it back until the S11 phase is 180 degrees greater than for the shorter cable.

Then, install both connectors on the cut ends. The connectors will add the same length to both cables, so they'll still be 90 degrees apart.

If I make a mistake, I measure the longer cable, and cut the shorter until the S11 phase is 180 degrees less than the longer.

cut one a quarterwave shorrter on 435 ... that would be 17cm x vf (0.8)

... 17.24x 0.8 = 13.8... so meachanical one should be roughly 13.8 cm

shorter ...

how to measure?? you can measure the complete length ... and calculate

its resonant length (and its harmonics!!)

do the same with the other wire ... and then a bit of math and you can

solve it

remember one is one quarterwave longer (or shorter) and has different

"harmonics" then ... so say one is 2m exact .. that is 14.5 quarterwaves

on 435 megs (200/ 13.792 = 14.5)

the other should be 200-13.8 = 186.2 cm ...

resonant length of the two??

you measure an open stup with a t connector and a dummy load

and look for the first quarterwave resonance dip as a short ... or

halfwave resonance as an open in parallel to the dummy

with the above values what the meachanical length should be ... you can

calculate what electricval length they should have (velocity factor!!)

and that can be checked easy with a vna

dg9bfc sigi

Am 27.02.2022 um 17:39 schrieb Ismo:

Thank you very much of those infos, now I’m gonna make some test cables.

Another thing is, how accurate the phase delay must be for circular polarization?

br ismo, OH1NHW

On 2/28/22 9:33 PM, Ismo wrote:

> Thank you very much of those infos, now I’m gonna make some test cables.

> Another thing is, how accurate the phase delay must be for circular

> polarization?

>

> b

That just affects your axial ratio. Are you sending/receiving to

something with linear pol or circular?

10 degree phase error, with no amplitude error, is a axial ratio of 1.5dB

See Figure 6

https://archive.org/details/wjtechnotesv06n4

hi,

What I did was this;

First took 200mm pure cable, installed one connector, measured the length I got 13mm longer.

So, connector will add +13mm.

Then cut (1/4 x VF)+13mm from that second cable which was same length 2080mm as cable no. one.

Installed N-connector and measured phase with Nano Saver.

Longer one (cable no. one) I got +139,7˚, this shorter one I got -39,86˚.

So 139,7 + 39,86 = 179,56 divided by 2 is 89,78˚

Pretty close I would say...

br ismo

On 3/1/22 10:24 AM, Ismo wrote:

> hi,

>

> What I did was this;

> First took 200mm pure cable, installed one connector, measured the

> length I got 13mm longer.

> So, connector will add +13mm.

> Then cut (1/4 x VF)+13mm from that second cable which was same length

> 2080mm as cable no. one.

> Installed N-connector and measured phase with Nano Saver.

> Longer one (cable no. one) I got +139,7˚, this shorter one I got -39,86˚.

> So 139,7 + 39,86 = 179,56 divided by 2 is 89,78˚

> Pretty close I would say...

>

Yes indeed.. That 0.22 degrees is probably less than the variability

from the antenna elements moving in the wind.

Not wanting to rain on anyone's parade but are you saying, Jim, that

the sign of the phase value is irrelevant?

Mathematically:

(+139.7) + (-39.86) = 99.84

Dave, G1OGY

On Tue, 1 Mar 2022 at 20:25, Jim Lux <jim@luxfamily.com> wrote:

hi,

Thank for your comments and info.

Cables are for the remote controlled polarization switch, take a look from Wimo.

https://www.wimo.com/en/18082

I have X-Quads for Vhf & Uhf and rem. ctlr-boxes for both, all from Wimo.

br ismo

Hi,

Please read the WIMO remote control box user manual .

We can easy read this:

[image: image.png]

Hope this can help you for your phase cables.

Anyway there is something wrong with your vna , you should not have some

"random zebras" on the screen...

Check again with a new calibration. start with well known components egg

attenuator, reactance capacitance to be sure there is no a hardware issue,

because I already saw in the pas same trace with burned input vna. i hope

I'm wrong for you.

73

Patrice.

Le mer. 2 mars 2022 à 09:51, Ismo <oh1nhw@gmail.com> a écrit :

You want *the difference* - Ismo had it right +139.7 - (-39.86) = 179.56.

They're reflection measurements, not thru, so they're double the actual phase, so he divided by 2.

90 degrees is ok.. Just depends on what cable goes to what element of the two

Dg9bfc sigi

Am 02.03.2022 15:35 schrieb Jim Lux <jim@luxfamily.com>:

> You want *the difference* - Ismo had it right +139.7 - (-39.86) = 179.56.

>

> They're reflection measurements, not thru, so they're double the actual

phase, so he divided by 2.

_._,_._,_

* * *

Jim

Thanks for straightening me out.

Dave, G1OGY

On Wed, 2 Mar 2022 at 14:35, Jim Lux <jim@luxfamily.com> wrote:

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