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Dr. David Kirkby from Kirkby Microwave Ltd
On Thu, 10 Oct 2019 at 06:25, johncharlesgord via Groups.Io <johngord= [email protected]> wrote: A photo of the dissected barrel connector is at:
/g/nanovna-users/album?id=96185
--John Gord Em, enough said, I initially thought that the melted stuff was hot-melt glue. That might have worked better as a dielectric! -- Dr. David Kirkby, Kirkby Microwave Ltd, drkirkby@... Telephone 01621-680100./ +44 1621 680100 Registered in England & Wales, company number 08914892. Registered office: Stokes Hall Lodge, Burnham Rd, Althorne, Chelmsford, Essex, CM3 6DT, United Kingdom
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I have noticed the feedback that the newly sent NanoVNA-H sma F-F terminal will be replaced with tetrafluoroethylene.
hugen
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On Thu, Oct 10, 2019 at 03:17 AM, Kurt Poulsen wrote:
Wrong, the cables are part of the NanoVNA hardware and cancelled out during calibration.
That's Wrong. You cannot cancel bad cable effect with calibration. You can only reduce it for a little. For example, here is calibration+measurement performed with rg174 32 cm (which come with NanoVNA) and with rg405 10 cm. See attachment. The test cases are following: 1) perform calibration with rg174 2) measure rg174 1) perform calibration with rg405 2) measure rg405 If it were possible to eliminate bad cable effect (as you mentioned), both measurement will be exactly the same. But they are different, and rg174 are much worse.
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measurements for rg174 and rg405
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Hello
I also got the nano with a RG174 cable, which according to the label and the datasheets is 75 ohms.
Thus, 75 Ohm and 50 Ohm cables are compared. Oooops
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On Thu, Oct 10, 2019 at 03:22 PM, Gyula Molnar wrote:
Hello
I also got the nano with a RG174 cable, which according to the label and the
datasheets is 75 ohms.
Thus, 75 Ohm and 50 Ohm cables are compared. Oooops
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On Thu, Oct 10, 2019 at 02:55 PM, <qrp.ddc@...> wrote:
On Thu, Oct 10, 2019 at 03:17 AM, Kurt Poulsen wrote:
Wrong, the cables are part of the NanoVNA hardware and cancelled out during
calibration.
That's Wrong. You cannot cancel bad cable effect with calibration. You can
only reduce it for a little.
For example, here is calibration+measurement performed with rg174 32 cm (which
come with NanoVNA) and with rg405 10 cm. See attachment.
The test cases are following:
1) perform calibration with rg174
2) measure rg174
1) perform calibration with rg405
2) measure rg405
If it were possible to eliminate bad cable effect (as you mentioned), both
measurement will be exactly the same. But they are different, and rg174 are
much worse.
You should calibrate at the end of the cable and the difference in the picture measurements you show is caused by the cable length, not the cable quality.
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Hugen, if you don't believe the caption, then it's really 50 Ohm from another manufacturer, but for Chinese it's 75 Ohm.
See CABLE & WIRE.pdf at
or
Might the cable manufacturer mistakenly solder it?
RG174A/U is actually 50 Ohm.
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On Thu, Oct 10, 2019 at 10:50 AM, <hugen@...> wrote:
You should calibrate at the end of the cable and the difference in the picture
measurements you show is caused by the cable length, not the cable quality.
You're right in order to compare S11, there is need to perform OSL through cable. See measurement in attachment. Now rg174 looks almost the same, but still has worse performance. :)
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On Thu, Oct 10, 2019 at 11:03 AM, Gyula Molnar wrote:
RG174A/U is actually 50 Ohm.
You cannot believe marking, this is just some noname cable with any marking on it :) The cable that I got with NanoVNA is marked just as "RG174 ROHS". But it has some high mismatch, because I measure it with dummy load at the end it has high waves, VSWR varies from 1.00 to 1.14. When I do the same with RG405, there is no waves, VSWR is straight line with VSWR=1.01. So, it looks, like this "RG174" is really 75 ohm. It explains why it works bad :)
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Yes, some manufacturers also provide 75 ohm RG174 cable. The RG174 cable provided by NanoVNA-H is 50 ohm. I have checked the parameters of RG174 and RG316 cables. They are not ideal at 1 GHz. Obviously it would be better to use RG405 or RG142, but they are too hard and not suitable for portable devices. If you use it in the lab, I recommend using RG405 or RG142 cable.
hugen
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Hi,
Thanks for the answer, I didn't expect to get a lab weighing station :-)
Only a few days that see, the duality on the cable labeled it.
Its mechanical size is closer to 1.5C-2V.
One question for the knowledgeable:
what is the length of a measuring cable, which is also a calibration cable?
The TAPR has 1m and 3m in the description and 30cm ... 60cm elsewhere.
I understand that quality has to be paid for, I am looking for a compromise.
Thank you for replying.
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In addition, the newly released NanoVNA-H reduced the RG174 cable from 30cm to 20cm to reduce the loss. If I make a VNA with a frequency higher than 1GHz, I will use the RG316 cable. On large VNAs in the lab, it is common to use RG402 cables.
This is the cable parameter provided by China's cable manufacturer£º
hugen
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On Thu, Oct 10, 2019 at 12:00 PM, <hugen@...> wrote:
I have checked the parameters of RG174 and RG316 cables. They are not ideal at 1 GHz.
You're right. I got NanoVNA from your store and rg174 which come with your NanoVNA definitely has less than 75 ohm impedance. But it is also definitely higher than 50 ohm. See TDR step response in attachment. It looks that the real impedance of this rg174 is about 55 ohm. Obviously it would be better to use RG405 or RG142, but they are too
hard and not suitable for portable devices. If you use it in the lab, I
recommend using RG405 or RG142 cable.
I agree these rg174 is not best for precise measurements, but their quality is acceptable for usual amateur measurements, such as antenna and filter testing, etc. And I also agree, rg405 are too hard for typical usage, so these rg174 looks like best choice for nanoVNA kit. They are flexible and not so bad, they have acceptable performance for typical amateur measurements. Regarding to the cal-kit which you selected for NanoVNA, I'm not sure about S and O quality, but L load looks very good, my instance has 49.95 ohm and pretty flat response. It is better than other dummy loads that I got from China. Thanks for the good-chosen accessories.for your NanoVNA kit. I'm satisfied with it :) There are two minor issues that I found in your NanoVNA: 1) joystick quality is not good, it is very weak, I got one that has false triggering when you turn it right side. 2) shielding quality is not the best, it is like hand made, but it works after all So, if you're planning for a new issue for classic nanoVNA, please replace that joystick with something else, for example with buttons.
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On Thu, Oct 10, 2019 at 12:34 PM, <hugen@...> wrote:
If I make a VNA with a frequency higher than 1GHz, I will use the RG316 cable.
They are very weak. I have several rg316 with crimping SMA connectors bought from different sellers on aliexpress. They breaking very quickly, there is very weak connection between the braid and crimped SMA connector, so it stops works after 5-10 usages. I don't recommend it for often usage. I recommend to use cable with soldered connectors, they are more reliable.
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Hi qrp.ddc You are just observing how to cable is part of the NanoVNA instrument, it is totally irrelevant what you see is the input impedance of the Ch1 port seen thru a test cable and so what ? It will be different what ever cable you use. What you should observe is a S21 dB measurement of a DUT, that makes sense and you will see no difference. Think again what you are measuring. -----Oprindelig meddelelse----- Fra: [email protected] < [email protected]> P? vegne af qrp.ddc@... Sendt: 10. oktober 2019 08:57 Til: [email protected]Emne: Re: [nanovna-users] Very poor thru (barrel) supplied with NanoVNAs measurements for rg174 and rg405
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On Thu, Oct 10, 2019 at 01:25 PM, Kurt Poulsen wrote:
What you should observe is a S21 dB measurement of a DUT, that makes sense and
you will see no difference.
I see difference for S21 between rg405 and rg174 cable in attachment.
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Dr. David Kirkby from Kirkby Microwave Ltd
On Thu, 10 Oct 2019 at 07:03, <hugen@...> wrote: I have noticed the feedback that the newly sent NanoVNA-H sma F-F terminal
will be replaced with tetrafluoroethylene.
hugen I don¡¯t know how you intend supporting the inner connector, as tetrafluoroethylene is a colourless gas???? I assume that you mean polytetrafluoroethylene (PTFE, also called Teflon) Don¡¯t worry - your English is 1000 dB better than my Chinese??? Dave -- Dr. David Kirkby, Kirkby Microwave Ltd, drkirkby@... Telephone 01621-680100./ +44 1621 680100 Registered in England & Wales, company number 08914892. Registered office: Stokes Hall Lodge, Burnham Rd, Althorne, Chelmsford, Essex, CM3 6DT, United Kingdom
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Gyula Molnar
Kurt Poulsen
Oristo