Steven, For best accuracy you need to re-calibrate. This is especially true if you only have 101 data points since there will be more interpolation when you zoom. However if you are only interested in SWR or RL the interpolation feature (on H/H4 hardware and some other models) works very well. Here is a link to some actual measurements where I "zoomed in" on a 20 m dipole. /g/nanovna-users/topic/73210908#12926Roger
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Steven,
the 6MHZ and its surroundings from the first production may be even more interesting when the value of the cooling condenser was inadequate.
Read more on my web site.
--
Gyula HA3HZ ()
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On 12/7/21 7:12 AM, Steven Bailey via groups.io wrote: Hi all...am new to this group. Have a question about calibrating the NanoVNA. If I say calibrate from 3-30 Mhz...and then decide to look (or zoom in) at frequencies from say 5-6 Mhz...do I need to do another calibration from 5-6 Mhz?
For the standard nanovna, there's 101 points - so if you calibrate from 3-30 MHz, you have a cal point every 270 kHz.? When you zoom in, the software interpolates between those points. So over your 5-6 MHz, it will interpolate over the 7-8 points covering the range.? For the most part, it's unlikely that your VNA and connectors/cables (whatever you calibrated with) vary wildly in that range, so the results will be reasonably good.? The sort of guideline is that you don't want the *phase* of the uncalibrated reflection coefficient making a big fraction of a circle between points. If you want better performance (or you're seeing something wonky) then recalibrating over the 5-6 MHz range gives you a calibration point every 10 kHz. Realistically, this only makes a difference if you've got something unusual inside the calibration plane. I have been fooling with hooking up two VNAs back to back (to make all 4 measurements at once), so I have a "stub" inside the calibration plane. I'm working at low frequencies (<100 MHz), so the stub is really short. In another experiment, I'm doing measurements with the "cal kit" connected by relays at the end of 100 ft of coax (two antennas in a phased array).? That's long enough that at higher frequencies, I get more than one wavelength in the coax, and that could make the simple linear interpolation with widely spaced points not work right.
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You wouldn't have to, but the number of points it is calibrated for would be less in the smaller range. It's best to re-calibrate and get the benefits of all the calibration points in the new range. Zack W9SZ On Tue, Dec 7, 2021 at 9:14 AM Steven Bailey via groups.io <sbailey64= [email protected]> wrote: Hi all...am new to this group. Have a question about calibrating the
NanoVNA. If I say calibrate from 3-30 Mhz...and then decide to look (or
zoom in) at frequencies from say 5-6 Mhz...do I need to do another
calibration from 5-6 Mhz?
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Hi all...am new to this group. Have a question about calibrating the NanoVNA. If I say calibrate from 3-30 Mhz...and then decide to look (or zoom in) at frequencies from say 5-6 Mhz...do I need to do another calibration from 5-6 Mhz?
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Re: Not responding in AM broadcast band
Indeed it was and it seems to be giving me good measurements now with the antenna I am testing. With an antenna tuner I can get an impedance of 32 ohms at 1620 KHz which is my desired frequency. On another note, I talked with a friend of mine who is a retired RCA employee with a distinguished past and he was impressed that a piece of test equipment like this can be had for about $100 and I am impressed too. If operated with its limitations in mind this is a fantastic device especially after I flashed one of the better firmwares available in the files section.
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Re: Not responding in AM broadcast band
Yes! That's the kind of thing I was trying to get you to find. That type
of mechanical issue is almost always the problem when something that was
working suddenly stops, especially after manipulating the setup, even in
innocuous ways. It's often in the least expected place.
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On Mon, Dec 6, 2021, 7:14 PM Nicholas <n.moon@...> wrote: I found the center conductor and dielectric and after putting them back in
the VNA is responding correctly through out its full range. Sometimes a
little poking around can solve a huge problem.
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Re: Not responding in AM broadcast band
I found the center conductor and dielectric and after putting them back in the VNA is responding correctly through out its full range. Sometimes a little poking around can solve a huge problem.
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Re: Not responding in AM broadcast band
On 12/6/21 7:01 PM, Nicholas wrote: A little embarrassing but I think I found the problem. I checked the SO-238 to BNC male adapter I was using and THE CENTER CONDUCTOR IS MISSING! It likely got lost on a piece of coax that I was using at one point. I am going to find it and put it back in. That would certainly result in an open no matter what antenna I use! A classic problem is when someone "stretches" a piece of coax to make it reach (or when pulling through a conduit or around something else), and the center conductor pulls back within the shield, taking the center pin with it.
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Re: Not responding in AM broadcast band
A little embarrassing but I think I found the problem. I checked the SO-238 to BNC male adapter I was using and THE CENTER CONDUCTOR IS MISSING! It likely got lost on a piece of coax that I was using at one point. I am going to find it and put it back in. That would certainly result in an open no matter what antenna I use!
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Re: Not responding in AM broadcast band
The cable tests correctly at DC with a multimeter with the braids connected and the center conductors connected correctly. The setup I have is exactly the same as when it was working correctly but just out of curiosity, what test are you talking about that might get me closer to a solution.
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Re: Not responding in AM broadcast band
When I have a problem like this, when something working suddenly stops, my
first impression would be that a connection/cable has a problem. So I
check each carefully. Sometimes a cable is broken right inside the
connector, and works fine until it is bumped; or a connector isn't reliable
when disconnected from one setup and moved to another. So I always check
those issues carefully first. Of course, I also check that the nano
input/output isn't broken by doing a simple test that I have seen work
before.
In this case you seem to have indicated (without including details) that it
gives you an 'open' indication after you changed your setup, so it could
well be that it is indeed open because of a bad cable or connection.
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On Mon, Dec 6, 2021 at 10:43 AM Nicholas <n.moon@...> wrote: I calibrated it for the upper edge of the AM band, 1600 to 1700 KHz and it
worked really well before with the calibration done in this range. For some
reason with calibration done in the same range it is not working at all
suddenly. I have never exceeded the specifications for transmitter input
power being very careful about where I set that for a transmitter under
test and I have followed the directions for calibration exactly including
some extra steps which would be useful the ISOLAT and THRU calibration
steps to be exact. It is just confusing to me why this would suddenly
happen.
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Re: Not responding in AM broadcast band
I calibrated it for the upper edge of the AM band, 1600 to 1700 KHz and it worked really well before with the calibration done in this range. For some reason with calibration done in the same range it is not working at all suddenly. I have never exceeded the specifications for transmitter input power being very careful about where I set that for a transmitter under test and I have followed the directions for calibration exactly including some extra steps which would be useful the ISOLAT and THRU calibration steps to be exact. It is just confusing to me why this would suddenly happen.
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Re: Not responding in AM broadcast band
What frequency range are you calibrated for? Perhaps recalibrate for a narrower range spanning the AM broadcast band, say 200 kHz to 2500 kHz.? Good luck.
Ken - WB?OCV
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On Dec 5, 2021 12:43, Nicholas <n.moon@...> wrote:
For some strange reason my NanoVNA is now not responding correctly to any
antenna designed for the AM broadcast band and instead is showing it as an
open. I have confirmed the calibration using the test loads and it looks
perfect so I am not sure what is going on here.
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Re: Not responding in AM broadcast band
What frequency range are you calibrated for? Perhaps recalibrate for a narrower range spanning the AM broadcast band, say 200 kHz to 2500 kHz.? Good luck.
Ken - WB?OCV
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On Dec 5, 2021 13:52, Nicholas <n.moon@...> wrote:
It was working perfectly in the AM broadcast band before both the S21 and
S22 connectors so I don't think that is the problem. The nearest AM radio
station to me is about six miles away and I am using the upper edge of the
band but that is a reasonable possibility.
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Those creations will likely work adequately for HF frequencies and below.
But at VHF and above, the leads and composition of the resistors will cause
some issues due to the parasitic inductance.
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On Sun, Dec 5, 2021 at 11:21 AM <Neil2Com@...> wrote: try these out,, i too have been trying to get better cal kit just for the
nanovna, i made set of
so239 (see my post "Calibration, Compensation, DIY Parts Hacking!...... My
First Post!") and i think
its ok but i still want to order these(
) and see if my tinkering is ok,
plus having a factorie cal set will let me build more stuff knowing i have
more then one standard to rely/test on on.. good
luck
KK6DBR
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Re: Not responding in AM broadcast band
I checked it elsewhere and it does not seem to be responding at all below 50 MHz so it is not just the AM broadcast band but also HF and to an extent low VHF as well.
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try these out,, i too have been trying to get better cal kit just for the nanovna, i made set of
so239 (see my post "Calibration, Compensation, DIY Parts Hacking!...... My First Post!") and i think
its ok but i still want to order these( ) and see if my tinkering is ok, plus having a factorie cal set will let me build more stuff knowing i have more then one standard to rely/test on on.. good
luck
KK6DBR
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Thanks for a great reference, Roger. There's much to be learned in that video.
73, Ralph Bolt, K?RO
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Thanks Jim. I tried it with good success.
73, Ralph Blt, K?RO
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Roger Need
HA3HZ
KK6DBR
Ralph Bolt, K?RO