Re: New NanoVNA bad USB cable or serial port?
Thanks Robin, that is most helpful. After your post I looked around and found a short type C to A cable, and sure enough the VNA was fine. It was just the cable squeezed into the box that must have broken it. Unfortunately I had already arranged to return it, and didn't want to risk fouling up the process by cancelling the return. Hopefully I will get one returned in a week or so with a good cable.
--
Dennis WA5LXS
|
Re: How low should a return loss at CH0 be?
This is a return loss to VSWR table. At 40 dB return loss the VSWR would be
1.02:1. A return loss of 14dB/VSWR 1.5:1 would be good for a typical filter.
*Clyde K. Spencer*
toggle quoted message
Show quoted text
On Thu, Jan 28, 2021 at 4:28 PM Leif M <leif.michaelsson@...> wrote: I just noticed that I can't get return loss better than about 40dB even
with a 30dB attenuator. With 60cm/2 feet of RG58 cable the return loss was
wavy like with impedance missmatch. I have calibrated the VNA from 50k to
300M. I guess I have to calibrate the VNA again.
FYi: I tried to measure an RF filter, made with an open stub in the
middle of cable. It was too broad to be of use.
|
How low should a return loss at CH0 be?
I just noticed that I can't get return loss better than about 40dB even with a 30dB attenuator. With 60cm/2 feet of RG58 cable the return loss was wavy like with impedance missmatch. I have calibrated the VNA from 50k to 300M. I guess I have to calibrate the VNA again.
FYi: I tried to measure an RF filter, made with an open stub in the middle of cable. It was too broad to be of use.
|
On Thu, Jan 28, 2021 at 09:03 AM, John Cunliffe W7ZQ wrote:
I assume you are calibrating the nano with the pigtail installed? If not, you
are comparing apples with oranges. Unless the load is a pure restive load with
no inductive or capacitive components the added length of the pigtail will
cause a change in the vswr as it acts like a transformer of the impedance and
can very well result in the different curves you are seeing. If you don't have
a way to calibrate the nano at the end of the pigtail you can add an equal
electrical length of coax cable to the rig expert setup.
Sorry but adding a short pigtail will not be an "apples to ranges" comparison. The complex impedance will change when you add a short pigtail to a long feedline but the VSWR change will be minimal. The reason is that the complex impedance change will result in a phase angle change to the reflection coefficient but the magnitude of the reflection coefficient will only be a tiny fraction smaller. You can easily verify this on a Smith chart or by adding a few feet of coax to a feedline and then measuring VSWR.
|
Instead of using an antenna which does capture ambient fields as your comparison standard, find and use non-reactive resistors as you 'gold standard'. You can also install series/parallel reactive components of well known values around the resistive elements. That way, the potential of interfering ambient fields are out of the picture. Dave - W?LEV On Thu, Jan 28, 2021 at 5:03 PM John Cunliffe W7ZQ <n2nep@...> wrote: I assume you are calibrating the nano with the pigtail installed? If not,
you are comparing apples with oranges. Unless the load is a pure restive
load with no inductive or capacitive components the added length of the
pigtail will cause a change in the vswr as it acts like a transformer of
the impedance and can very well result in the different curves you are
seeing. If you don't have a way to calibrate the nano at the end of the
pigtail you can add an equal electrical length of coax cable to the rig
expert setup.
-- *Dave - W?LEV* *Just Let Darwin Work*
|
I assume you are calibrating the nano with the pigtail installed? If not, you are comparing apples with oranges. Unless the load is a pure restive load with no inductive or capacitive components the added length of the pigtail will cause a change in the vswr as it acts like a transformer of the impedance and can very well result in the different curves you are seeing. If you don't have a way to calibrate the nano at the end of the pigtail you can add an equal electrical length of coax cable to the rig expert setup.
|
John,
if you want to get, say, 3000? choking impedance on UHF, broadband, I can only wish you good luck! Because at 3000? at 500MHz is what a 0.1pF stray capacitance has. So forget about winding multiple turns on a core.
The best thing you ca do, I think, is find out which beads or toroids provide the highest impedance per length over the frequency range you need, and stack as many of them as necessary on your transmission line.
Manfred
|
Re: [nanovnav2] CMCs - MORE (BAD) INFORMATION
I think FairRite makes toroid choke kits that comes with enameled wire and
Teflon tubing that slips over it. Not much more expensive than the bare
toroid.
|
Re: [nanovnav2] CMCs - MORE (BAD) INFORMATION
My W/C is on 40-meters where I measure 1161 - j1110 at 7.0 MHz. 700W on 1161? is a current of 0.776A. The impedance magnitude is 1606?, and so the voltage is 1246V RMS, which is 1762V peak. At 1500W it would be about 50% higher. That's what you have at the input of the CMC, which is where I understand you are measuring. Along the length of the winding the voltage could get higher or lower. By Murphy's Law it will get higher, of course... Even if the insulation of the magnet wire could take a million volt, it wouldn't be enough. This is because of Corona Effect. Consider a cut view through your bifiliar line: Two round copper wires, with a thin film of insulation around each, in direct contact, and with a wedge of air penetrating between the wires on each side. The problem is this wedge of air. With the insulation material having a dielectric constant of about 4 times that of air, the electric field gradient in the insulation is about 4 times lower than in the air. So, at a place where the air wedge has a suitable thickness, most of the voltage will appear across the air, rather than across the insulation thickness. Now it happens that air won't break down below roughly 300V, no matter how thin the air layer is. But at voltages above that level it can break down. When the air breaks down, microscopic arcing happens, and most of the voltage moves into the insulation layers, limiting the arcing. But it is there, right at the surface of the insulation, and will erode the insulation over time. Sooner or later it will fail. Depending on how strong the effect it, it might fail after several weeks, or after several milliseconds, or anywhere in between. So a magnet wire pair in direct contact can certainly work at somewhat more than 300V, because some of the voltage is dropping in the insulation, but not a huge lot more. Even if it has a very good insulation. The insulation must be thick enough, and its dielectric constant low enough, to never exceed the breakdown voltage of the air wedge. With insulated wires in direct contact, that's about 300V in the air, and if there is a significant spacing it gets higher. With enough spacing, of course, the air alone provides enough insulation. A better parallel transmission line would have the dielectric material molded around both conductors, filling the space between them, eliminating the air wedges. A thicker insulation helps a lot, and an insulation having the lowest possible dielectric constant also helps. This is why teflon is so good: It does have a low dielectric constant, so more of the field appears in the teflon and less in the air. An alternative is inserting a magnet-wire-wound CMC in a can of some suitable oil, and make sure no tiny air bubbles remain lodged between the wires. The downside of oil, of course, is that it increases the stray capacitance... My lowest impedance is at 2.0 MHz and measures 19 - j288 1500W on 19? is 8.89A. The magnitude of that impedance is 288.6?. So the voltage is 2566V RMS, or 3629V peak. And very likely you could have even higher voltage spots along the line in your CMC! You could measure the impedances with two different line lengths, both lines being of the same construction, for example using two of your CMCs having very different winding length. Then you can calculate what the highest voltage will be. But even without doing this, it's crystal clear that a CMC used on several bands in a high-SWR line, tuned/matched between the CMC and the transceiver, needs to be able to handle really high voltage, and pretty high current. Manfred
|
Re: File /Absolute Beginner Guide to The NanoVNA/Absolute_Beginner_Guide_NanoVNA_v1_6.pdf uploaded
#file-notice
Create a repo on github, it's free and others can send changes.
toggle quoted message
Show quoted text
On Thu, 28 Jan 2021 at 08:59, Martin J.K. <martin.svaco@...> wrote: The document is written in Microsoft Word and printed in PDF with PrimoPDF.
No protection is activated.
If anyone wants a word document I will gladly send to email but the word
document
is about 9 MB.
73
Martin 9A2JK
|
Dave - W?LEV
<<Generally, a few clamp-on ferrites of the appropriate material at the feedlint is all you really need. ..ferrites aimed at EMC and RFI control are good for that purpose at VHF/UHF frequencies
Unfortunately the Z of clamp-ons is a couple of hundred R at best; I'm looking for > 10 times that, eg for resonant feedline and end fed 1/2 wave antennae. So clamp on are inadequate
I should have said that I need broadband suppression, so 1/4 and 1/2 wave types are no use.
73
John
.
|
Re: File /Absolute Beginner Guide to The NanoVNA/Absolute_Beginner_Guide_NanoVNA_v1_6.pdf uploaded
#file-notice
The document is written in Microsoft Word and printed in PDF with PrimoPDF.
No protection is activated.
If anyone wants a word document I will gladly send to email but the word document
is about 9 MB.
73
Martin 9A2JK
|
Re: [nanovnav2] CMCs - MORE (BAD) INFORMATION
PTFE tubing from AliExpress:
$4 for 10m, ID 0.7mm OD 1.3mm will be ~100¦¸ for a parallel pair.
toggle quoted message
Show quoted text
On Thu, 28 Jan 2021 at 02:12, Jim Lux <jim@...> wrote: On 1/27/21 4:58 PM, n2msqrp wrote:
Because of the temperatures involved in the fabrication process solder would melt on plated stranded wire so teflon wire is either available
silver plated or bare copper wire.
It used to be available for a decent price at ham fests years ago. I
don't knoe know since the proce of all surplus wire has risen.
Mike N2MS
$650/for 100ft from Digikey - Alpha 5859/12 WH005 MIL-W-16878/4 Type E
$434/100ft for AT121925 WH005 (19/25 strand copper silver coated)
you could probably find a less expensive insulation that works as well,
but "dollars/ft" is what you're looking at.
I'll bet a lot of the cost is NOT the copper cost..
So running a 4 wire twist (2 in parallel) might actually be cheaper.
That would be AWG 15
AWG16 is about 129/100ft and TFE (not PTFE) insulation, still 600V,
still good to 200C.
and you can buy these things by the foot (even from Digikey).
On 01/27/2021 4:09 PM David Eckhardt <davearea51a@...> wrote:
I was also surprised it broke down, but every CMC I wound with solid #12
enameled wire broke down between 400 and 700 watts. I believe it has a
lot
I have not tried or thought of using teflon coated silvered conductor.
I
need to find it and, if not too expensive, give it a try.
|
Re: [nanovnav2] CMCs - MORE (BAD) INFORMATION
I found silver coated PTFE insulated stranded wire. It's a bit pricey, but
not out of reach.
The huge CMC I had decades ago was wound with #12 solid conductor. I had
slipped PTFE tubing over it before I wound it on the toroid. I no longer
have that tubing and need to find a source, but I'm now running low on #12
solid wire.
So, I may order some of the #12 Flex-weave antenna wire from DavisRF. I
know the #14 of similar design does OK at power.
Ideally, I'd rewind several of the cores that had my enameled #12 wire with
#12 solid conductor with PTFE tubing slipped over the wire.
I'll make my decision tomorrow.........
Dave - W?LEV
toggle quoted message
Show quoted text
On Wed, Jan 27, 2021 at 9:25 PM Doc <kjenkins5623@...> wrote: I have found that using regular magnet wire with teflon tubing slid over
the wire will easily handle 2KW. I have wound a number of 4:1 transformers
as well as 49:1 transformers for EFHW using this method. All the balun
designs use a similar scheme; most likely due to the cost and difficulty in
obtaining silvered wire.
Ken WB6MMV
On Wed, Jan 27, 2021 at 2:10 PM David Eckhardt <davearea51a@...>
wrote:
I was also surprised it broke down, but every CMC I wound with solid #12
enameled wire broke down between 400 and 700 watts. I believe it has a lot
to do with the impedances in which the CMCs are installed. My W/C is on
40-meters where I measure 1161 - j1110 at 7.0 MHz. My lowest impedance is
at 2.0 MHz and measures 19 - j288.
I have not tried or thought of using teflon coated silvered conductor. I
need to find it and, if not too expensive, give it a try.
I rewound the 400-31 single core with the DavisRF 'antenna' wire with no
problems to at least 1.2 kW. It is certainly better at CM impedance than
the 43 material especially on 160 and 75 meters but 43 is a bit better on
the higher bands - as expected.
Out of all the CMCs I've wound and tested, I have three that I can use, all
wound with the DavisRF #14 stranded and insulated antenna wire: 1)
240-31, 15 turns, 2) 300-43, 16 turns, and 3) 400-31, 21 turns. Those
remaining do not perform well under DM loss (rejection) or phase balance
(¦Ð-radians out of phase) and/or amplitude balance on the DM side. I'm
going shopping for Teflon coated silvered solid conductor.
Dave - W?LEV
On Tue, Jan 26, 2021 at 11:26 PM Jim Lux <jim@...> wrote:
On 1/26/21 3:04 PM, n2msqrp wrote:
Dave,
Have you tried teflon covered silver plated wire?
Mike N2MS The silver doesn't help much for RF conductivity, but it is a LOT easier
to solder to.
I'm kind of surprised that magnet wire broke down. Most magnet wire is
good for a kilovolt or so, because motors and transformers get hi-pot
tested at 2-5kV.
Decent insulated magnet wire
Catalog here:
AWG 12 copper bare is 0.0808 (nom)
single build is 0.0825 (i.e. the insulation is 8.5 mils (0.2 mm) thick
heavy build is 0.0842 is twice as thick. (0.4mm)
most plastics have breakdown strength of 20 kV/mm or more, especially
for thin layers.
PTFE (Teflon) and Polyimide (Kapton) are a lot better (100 kV/mm)
Polyester (Mylar) is in between (50kV/mm)
Note that thinner layers have a higher breakdown voltage per mm (that
is, you might find that a layer that's 0.1 mm and 1mm have almost the
same breakdown voltage)
Formvar is about 11kV as typically applied to wire.
On 01/26/2021 3:30 PM David Eckhardt <davearea51a@...> wrote:
Those wound with the #12 enameled solid conductor do not take power
with
my ant/feedline impedances resulting in discharges between bifilar
pairs
(not between individual bifilar windings). Also, the green wire of
unknown insulation does not take power. So, those CMCs wound with
solid
conductor are coming apart and being rewound in some fashion or
another
with the DavisRF "antenna" wire which seems to take power to at
least
1.2
kW. Your mileage may vary with different impedances presented to
the
chokes.
Those frequencies on which I tried the CMCs at power are:
3.8 MHz 24 - j56
7.15 MHz 493 - j740
Impedances noted are measured at the shack end of the parallel wire
feedline.
Dave
--
*Dave - W?LEV*
*Just Let Darwin Work*
--
*Dave - W?LEV*
*Just Let Darwin Work*
|
Re: [nanovnav2] CMCs - MORE (BAD) INFORMATION
On 1/27/21 4:58 PM, n2msqrp wrote: Because of the temperatures involved in the fabrication process solder would melt on plated stranded wire so teflon wire is either available silver plated or bare copper wire.
It used to be available for a decent price at ham fests years ago. I don't knoe know since the proce of all surplus wire has risen.
Mike N2MS $650/for 100ft from Digikey - Alpha 5859/12 WH005 MIL-W-16878/4 Type E $434/100ft for AT121925 WH005 (19/25 strand copper silver coated) you could probably find a less expensive insulation that works as well, but "dollars/ft" is what you're looking at. I'll bet a lot of the cost is NOT the copper cost.. So running a 4 wire twist (2 in parallel) might actually be cheaper. That would be AWG 15 AWG16 is about 129/100ft and TFE (not PTFE) insulation, still 600V, still good to 200C. and you can buy these things by the foot (even from Digikey).
On 01/27/2021 4:09 PM David Eckhardt <davearea51a@...> wrote:
I was also surprised it broke down, but every CMC I wound with solid #12
enameled wire broke down between 400 and 700 watts. I believe it has a lot
I have not tried or thought of using teflon coated silvered conductor. I
need to find it and, if not too expensive, give it a try.
|
Re: New NanoVNA bad USB cable or serial port?
Dennis, it is a USB-C connector. It should be reversible, with semi-circular, rather than sloping, ends to the socket & plug. Most modern mobile phones use these nowadays, since the possibility of plugging in upside down is eliminated by design. You might try using a mobile phone charger, or a powered USB hub, or another computer or other device. There are reports of issues with USB hardware on computers not recognising devices, which might be the issue you are having. HTH, 73, Stay Safe, Robin, G8DQX PS: The wiki ( /g/nanovna-users/wiki) is a good place to start.
On 27/01/2021 23:55, WA5LXS via groups.io wrote: Got my nifty NanoVNA yesterday. The unit works but it will not charge the battery nor will it be recognized by my Win PC. I suspect the USB cable is bad, but it could be the connector on the board. Anyone else experience this or have a ¡°fix¡±. I don¡¯t recognize the type of connector on the unit.
|
Re: [nanovnav2] CMCs - MORE (BAD) INFORMATION
Because of the temperatures involved in the fabrication process solder would melt on plated stranded wire so teflon wire is either available silver plated or bare copper wire.
It used to be available for a decent price at ham fests years ago. I don't knoe know since the proce of all surplus wire has risen.
Mike N2MS
toggle quoted message
Show quoted text
On 01/27/2021 4:09 PM David Eckhardt <davearea51a@...> wrote:
I was also surprised it broke down, but every CMC I wound with solid #12
enameled wire broke down between 400 and 700 watts. I believe it has a lot I have not tried or thought of using teflon coated silvered conductor. I
need to find it and, if not too expensive, give it a try.
|
New NanoVNA bad USB cable or serial port?
Got my nifty NanoVNA yesterday. The unit works but it will not charge the battery nor will it be recognized by my Win PC. I suspect the USB cable is bad, but it could be the connector on the board. Anyone else experience this or have a ¡°fix¡±. I don¡¯t recognize the type of connector on the unit.
--
Dennis WA5LXS
|
Re: Finally getting into my Gecko, only two traces
#newbie
Hi Bear,
Download and read one or more of the several user guides available in the files area of the forum??
Since this is your first time,? read the absolute beginner's guide. Also, since you have a Gekko, it probably has really old firmware so read up on how to update your device.?
Lastly,? please browse the forum wiki??
On Wed., 27 Jan. 2021 at 7:08 p.m., Bear Albrecht
<W5VZB.NM@...> wrote: I finally started learning about this thing and all the videos I've seen so far show four traces.? I've only got two.? Do I need a firmware update, or what?
|
Re: Finally getting into my Gecko, only two traces
#newbie
yes there are many versions avalible versions I will do some research I
need to update mine as well as I only have 2 traces also.
toggle quoted message
Show quoted text
On Wed, Jan 27, 2021, 5:09 PM Bear Albrecht <W5VZB.NM@...> wrote: I finally started learning about this thing and all the videos I've seen
so far show four traces. I've only got two. Do I need a firmware update,
or what?
|
WA5LXS
Roger Need
BryonB