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I¡¯m guessing that with a 75-ohm calibration it might be.
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Is this Russian site the only option for firmware? (I am working with the online translators but it is slow going.)
For those that know the NanoVNA code, what needs to be changed for measuring 75-ohm cable? Anything, or is it just calibrate with 75-ohm load and go?
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To my knowledge, Xenomorph is the only one who has created a firmware version for testing 75 ohm systems.
I will place a file containing his firmware and instructions in the Firmware folder on this forum.
Regards,
Larry
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On Thursday, October 10, 2019, 10:49:16 a.m. GMT-4, S Johnson <cascadianroot@...> wrote:
Is this Russian site the only option for firmware? (I am working with the online translators but it is slow going.)
For those that know the NanoVNA code, what needs to be changed for measuring 75-ohm cable? Anything, or is it just calibrate with 75-ohm load and go?
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Dr. David Kirkby from Kirkby Microwave Ltd
On Thu, 10 Oct 2019 at 03:24, S Johnson <cascadianroot@...> wrote: I¡¯m guessing that with a 75-ohm calibration it might be. Whilst I accept 75 ohms is the 2nd most common impedance after 50 ohms, it would be nice if *any* impedance could be a supported. The bridge itself is 50 ohms, but there are two ways around this 1) Minimum loss pads can be used to allow calibration with 75 ohm calibration kits. There are 75 ohm versions of both N and BNC connectors, and calibration kits for both available. The F connector is only 75 ohms and calibration kits for F - my company has both mechanical and electronic kits for F. 2) One may wish to calibrate with a 50 calibration kit, but have all S parameters showed compared some other impedance. For example, I have an application where it would be nice to have 112 ohms in the centre of the Smith Chart. 3) Whilst I admit it is a bit unlucky that waveguide would be used with a NanoVNA, it is not totally impossible. I have seen waveguide suitable for 450 MHz for a professional application. It seems standard practice to configure the VNA for 1 ohm in that case. So it would be nice if all references to 50 ohm removed from the firmware. 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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Why not make the impedance a selected item in the firmware with a default to 50 but allow manual input within a fixed range?
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On Thursday, October 10, 2019, 12:33:05 p.m. GMT-4, Dr. David Kirkby from Kirkby Microwave Ltd <drkirkby@...> wrote: On Thu, 10 Oct 2019 at 03:24, S Johnson <cascadianroot@...> wrote: So it would be nice if all references to 50 ohm removed from the firmware. Dave
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Dr. David Kirkby from Kirkby Microwave Ltd
On Thu, 10 Oct 2019 at 17:42, Larry Rothman <nlroth@...> wrote: Why not make the impedance a selected item in the firmware with a default
to 50 but allow manual input within a fixed range? Yes. I did mean that to be detault behave, despite what I wrote would not have achieved that
On Thursday, October 10, 2019, 12:33:05 p.m. GMT-4, Dr. David Kirkby
from Kirkby Microwave Ltd <drkirkby@...> wrote:
On Thu, 10 Oct 2019 at 03:24, S Johnson <cascadianroot@...> wrote:
So it would be nice if all references to 50 ohm removed from the firmware. Dave
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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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Firmware for 75 Ohm "device" 12.10.2019
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On Fri, Oct 11, 2019 at 06:18 PM, DMR wrote:
Firmware for 75 Ohm "device" 12.10.2019
------------------------------------------------------------------------------- DMR, Thanks for your contribution. A previous DFU file was uploaded for making 75 ohm system measurements ("50-75 Ohm_Use transformer-10.10.2019.ra"). The uploader made special note that in order for measurements to be accurate 50-75 ohm matching pads were required on CH0 and CH1. Does your mod also require matching pads/transformers, or are you applying some type of mathematical correction factor? - Herb
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On Thu, Oct 10, 2019 at 09:33 AM, Dr. David Kirkby from Kirkby Microwave Ltd wrote:
1) Minimum loss pads can be used to allow calibration with 75 ohm
calibration kits. There are 75 ohm versions of both N and BNC connectors,
and calibration kits for both available. The F connector is only 75 ohms
and calibration kits for F - my company has both mechanical and electronic
kits for F.
David, Could you give the group a short form on how this is done, and what a NanoVNA user would do and see to measure something like a piece of RG6 or a 75-300 ohm transformer? Not to take away from your sales, but what kind of error would a pad made from 1% carbon resistors introduce, compared to a commercial pad?
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Found a nice website from Jacques Audet, VE2AZX, (English and French) which has some Excel spreadshhets for VNA S11 values. It seems to provide measurement corrections from 50 ohm cal to 75 ohm system measurements. Also some practical examples of impedance and antenna measurements.
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Dr. David Kirkby from Kirkby Microwave Ltd
On Sat, 12 Oct 2019 at 03:37, Starsekr via Groups.Io <Starsekr= [email protected]> wrote:
David,
Could you give the group a short form on how this is done, and what a
NanoVNA user would do and see to measure something like a piece of RG6 or a
75-300 ohm transformer? Not to take away from your sales, but what kind of
error would a pad made from 1% carbon resistors introduce, compared to a
commercial pad?
I don¡¯t sell 75 ohm kits, neither do I sell matching pads - only 50 ohm kits and consultancy services. I heard a report somewhere on here that the receiver port on the NanoVNA is not particularly close to 50 ohms and varies on the batch a given device is from. That¡¯s something I would like to fix myself, which could be done with a few 1% resistors, after measuring the impedance. 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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You know, after all the talk about matching impedances, I'm really
wondering .... we talk about POWER in watts but that's pretty much for
transmitters. But we talk about receivers in? VOLTS. Well, okay, microvolts,
usually. Somehow, I don't see a good reason to CARE about matching
receiver input impedance. Maybe it lowers the antenna bandwidth or Q?
Impedances have PHASE, but voltages do not. Care to comment?
Bill
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On 10/12/19 6:50 AM, Dr. David Kirkby from Kirkby Microwave Ltd wrote: On Sat, 12 Oct 2019 at 03:37, Starsekr via Groups.Io <Starsekr=
[email protected]> wrote:
David,
Could you give the group a short form on how this is done, and what a
NanoVNA user would do and see to measure something like a piece of RG6 or a
75-300 ohm transformer? Not to take away from your sales, but what kind of
error would a pad made from 1% carbon resistors introduce, compared to a
commercial pad? I don¡¯t sell 75 ohm kits, neither do I sell matching pads - only 50 ohm
kits and consultancy services.
I heard a report somewhere on here that the receiver port on the NanoVNA
is not particularly close to 50 ohms and varies on the batch a given device
is from. That¡¯s something I would like to fix myself, which could be done
with a few 1% resistors, after measuring the impedance.
Dave
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Does not a mismatch create problems with loss and noise?
If I connect a 50 ohm coax to a 300 ohm TV antenna, without a
transformer, should I not anticipate a poor quality received signal?
Or am I misunderstanding?
David, KD4E
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You know, after all the talk about matching impedances, I'm really
wondering .... we talk about POWER in watts but that's pretty much for
transmitters. But we talk about receivers in? VOLTS. Well, okay, microvolts,
usually. Somehow, I don't see a good reason to CARE about matching
receiver input impedance. Maybe it lowers the antenna bandwidth or Q?
Impedances have PHASE, but voltages do not. Care to comment?
Bill
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Does not a mismatch create problems with loss and noise?
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Somehow, I don't see a good reason to CARE about matching
receiver input impedance. Maybe it lowers the antenna bandwidth or Q? Certainly Q, which is good or bad, depending on application. Mismatch also plays with imbalance, so that e.g. coax from antenna to receiver can effectively become part of antenna, picking up noise between outdoor antennas and indoor receivers.
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Right on! There are many questions that don't seem to be asked, and answers don't
always much sense without some hands-on tests and data.
I got started with this round watching comparisons of assorted Baofeng-type antennas
for those really cheap Chinese walkie-talkies. (on youtube)
Then I got to wondering what difference does the impedance make.
One thing that makes some experimenting easy is telescoping antennas like the Nagy -704.
You can move the ''resonance'' all over the place!? For test signals there's things like garage door
openers and tire-pressure sensors.
Bill
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On 10/12/19 1:32 PM, David KD4E wrote: Does not a mismatch create problems with loss and noise?
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On Sat, Oct 12, 2019 at 09:06 PM, Bill Hemmings wrote:
Somehow, I don't see a good reason to CARE about matching
receiver input impedance.
it doesn't related with volts or watts, impedance mismatch has the same poor effect for any volts and watts. Impedance mismatch just reduce signal level. But when you use cable, there is another issue - standing wave in the cable. Standing wave multiplies all losses in the cable. This is why standing wave in the cable leads to dramatic signal loss. When you use TX, standing wave in the cable depends on cable load impedance (antenna). This is why it is very critical to match your cable with antenna. Note, I wrote cable (not TX output), this is not mistake, you're needs to match your cable impedance with antenna. When you use RX, standing wave in the cable depends on cable load impedance (receiver input impedance). This is why antenna match is not critical for RX. But for RX you're needs to match your RX input with cable impedance, otherwise you will have the same issue as for TX. If you use RX with proper impedance match between RX input and cable impedance (both impedances should be equals, for example 50 ohm), there is no standing wave in the cable. If your antenna has bad impedance match with cable, it just will leads to low signal level, but there is no multiple losses and distortions in the cable due to standing wave, because there is no standing wave. Your receiver can use high gain amplifier in order to compensate low signal level from antenna. This is why antenna match is not critical for receiver. The same output impedance of transmitter is not critical, it just leads to lower efficiency, but there is no multiple losses and distortions due standing wave. Because standing wave is missing when you transmit to antenna which has good match with cable.
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Starsekr
Oristo
