Re: Antenna / VNA Question
D.? The 468 rule of thumb is not that accurate.
That is just a good starting point.? ?It does not allow for the diameter of the conductor or any nearby objects.? The difference between bare Copper Wire and Insulated Copper wire can be as much as 10% difference.? ? ? Any nearby insulating material? 'dielectrics' will lower the resonate frequency of an antenna.? ? Good luck with your project, Kent WA5VJB
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On Wednesday, September 22, 2021, 09:16:33 AM CDT, Andrew Kurtz via groups.io <adkurtz@...> wrote:
I have a dipole antenna in my attic, made of bare 14 gauge copper wire.? It is 49.916 feet long, and the feed point is within 1.5 inches of the center.? Thus, the ¡°rule¡± that f=468/L suggests the optimal, tuned frequency should be 9.38 MHz (right?).? And at that frequency X should be about 0 and R should be radiative R at about 75 ohms (right?).? 55 feet of ¡°300 ohm¡± twin-lead connects this balanced antenna to my ¡°shack¡± in the basement.
In the basement, I analyzed the "twin-lead plus dipole" using my nanoVNA-H4, calibrated with 100 points each between 0.5 and 5 MHz, then 5 and 10 MHz, then 10 and 15 MHz, then 15 and 25 MHz.? The outputs looked very reasonable (I think):? Smith charts making nice circles, reactance X rising periodically from capacitive to inductive smoothly, then crashing very fast from inductive to capacitive, and real R and SWR lowest where X is rising and quite high where X is falling.
But here comes the question:? minimum R and SWR, and X crossing 0 from capacitive to inductive, occurred at 3.1, 8.1, 11.5, 17.3, and 23.6 MHz ¡ª nowheres near the expected 9.38 MHz.? Also, I can¡¯t see a regular multiple of wavelength between those frequencies.? Here are possible answers:
? ? A.? My understanding is incorrect.? (I am very new to RF stuff.)
? ? B.? The feed line really changes things.? And do you advise some sort of balun between antenna and twin-lead or twin-lead and receiver?
? ? C.? The nanoVNA is not that accurate.
? ? D.? The 468 rule of thumb is not that accurate.
By the way, the minimum resistance measured at each apparent tuned frequency was around 30 ohms, versus the expected 76 or so.? Is this significant?
? Andy
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I have a dipole antenna in my attic, made of bare 14 gauge copper wire. It is 49.916 feet long, and the feed point is within 1.5 inches of the center. Thus, the ¡°rule¡± that f=468/L suggests the optimal, tuned frequency should be 9.38 MHz (right?). And at that frequency X should be about 0 and R should be radiative R at about 75 ohms (right?). 55 feet of ¡°300 ohm¡± twin-lead connects this balanced antenna to my ¡°shack¡± in the basement.
In the basement, I analyzed the "twin-lead plus dipole" using my nanoVNA-H4, calibrated with 100 points each between 0.5 and 5 MHz, then 5 and 10 MHz, then 10 and 15 MHz, then 15 and 25 MHz. The outputs looked very reasonable (I think): Smith charts making nice circles, reactance X rising periodically from capacitive to inductive smoothly, then crashing very fast from inductive to capacitive, and real R and SWR lowest where X is rising and quite high where X is falling.
But here comes the question: minimum R and SWR, and X crossing 0 from capacitive to inductive, occurred at 3.1, 8.1, 11.5, 17.3, and 23.6 MHz ¡ª nowheres near the expected 9.38 MHz. Also, I can¡¯t see a regular multiple of wavelength between those frequencies. Here are possible answers:
A. My understanding is incorrect. (I am very new to RF stuff.)
B. The feed line really changes things. And do you advise some sort of balun between antenna and twin-lead or twin-lead and receiver?
C. The nanoVNA is not that accurate.
D. The 468 rule of thumb is not that accurate.
By the way, the minimum resistance measured at each apparent tuned frequency was around 30 ohms, versus the expected 76 or so. Is this significant?
Andy
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$23.99 ???? for a tool that usually costs a few bucks
in any network equipment store, not to mention the usual Chinese
vendors on Ali and Ebay.
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On Wed, 22 Sept 2021 at 14:58, RandMental <randmental@...> wrote: I bought these for RG213 and RG58 - Don¡¯t waste your money
Still using a carpet knife and side cutter!
-----Original Message-----
From: [email protected] <[email protected]> On Behalf Of
DougVL
Sent: Wednesday, September 22, 2021 12:29 PM
To: [email protected]
Subject: Re: [nanovna-users] Stripping Coax
Check
<>
--
Doug, K8RFT
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I'd imagine 'not the shield', aka the ('hot'?) center conductor.
73, Willie N1JBJ
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On Sep 19, 2021, at 1:44 PM, Mike C. <mg@...> wrote:
What is a "warm" wire in the CH0 connector??
On 9/19/2021 11:32 AM, eugen.trifu@... wrote:
I had the same problem, which appears when making the calibration and SHORT probe does no electric contact is made with the CH0 connector.
Solving was by tightening the warm wire in the CH0 connector.
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The typical life of flash in many SOC micros is around 10K erase/write cycles.?
I found this link on an STM32 forum that has some good tips on extending flash life.?
I had asked several months ago how difficult it would be to add an 8 pin SPI flash chip (eg:25f128)? to the NanoVNA for extra storage space.? ?Is support already in the ChibiOS routines? The Nano-F has this.
?I have 25f256 chips I can attach to my H,H4 to test any routines with.
Thanks,
Larry
On Wed., 22 Sep. 2021 at 12:21 a.m., DiSlord<dislordlive@...> wrote: In my last firmware i add option DONE IN RAM (in calibration menu)
This allow do calibration and not save it in flash (prevent flash damage from frequent rewriting, and not need use save slot)
This calibration reset after device power off.
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What is a "warm" wire in the CH0 connector??
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On 9/19/2021 11:32 AM, eugen.trifu@... wrote: I had the same problem, which appears when making the calibration and SHORT probe does no electric contact is made with the CH0 connector.
Solving was by tightening the warm wire in the CH0 connector.
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Re: PC Boards for QEX Step Attenuator Available
The author discusses this some and there are numerous response graphs in the QEX supp files. Can you read the article or do you need a copy
Dick K9IVB
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In my last firmware i add option DONE IN RAM (in calibration menu)
This allow do calibration and not save it in flash (prevent flash damage from frequent rewriting, and not need use save slot)
This calibration reset after device power off.
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On 9/21/21 2:05 PM, William Smith wrote: OK, that's adjustable for different jacket/braid/dielectric/center diameters, do you have to swap the cartridge for different strip lengths?
73, Willie N1JBJ
yes and no. There's a bunch of "slots" into which the blade drops to adjust the "length". Then the hex screw sets the depth. If you're using two kinds of strips consistently, then getting extra cassettes is useful. I just used to keep notes on where to put the blade, and how many turns of the hex for each one. And eventually, the blade does get dull (esp the one cutting the shield in the middle). On Sep 21, 2021, at 4:58 PM, Jim Lux <jim@...> wrote:
On 9/21/21 1:20 PM, William Smith wrote:
Hey Jim,
Do you have a pointer to the fancy adjustable one? I've been having a hard time finding anything other than 2 and 3 blade non-adjustable ones
73, Willie N1JBJ Paladin CST Pro
looks like it
On Sep 21, 2021, at 2:56 PM, Jim Lux <jim@...> wrote:
the fancy adjustable one
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Depending upon the version of the NanoVNA and the firmware version the
NanoVNA uses 101, 201, 301, or 401 points of measurement. That says that if
you have a calibration range of 3 to 30 MHz and the device is using 101
points the NanoVNA measures approximately every 267 KHz.Now if you reduce
the range to the 7050 to 7060 MHz that is 10 KHz. That is very much less
than the 267 KHz used by the device. Yes the device is still calibrated for
the 3 to 30 MHz but may not accurately measure the narrower span. EXAMPLE
1st point is 3000 KHz
2nd point is 3267 KHz
3rd point is 3534 KHz
and so on.......
I would recommend that you calibrate the 3 to 30 MHz range for
board measurements but also due an additional calibrate in the specific
frequency range of interest. If you calibrated in the 7000 to 7100 range
then there will be a measurement point every 990 Hz.
The basic rule is to recalibrate with changes in frequency or changes in
jumper cable length.
The numbers quoted are approximate.
Regards,
*Clyde K. Spencer*
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On Tue, Sep 21, 2021 at 7:03 PM Joe WB9SBD <nss@...> wrote: Ok,
say I set up Stimulus for 3 to 30 Mhz.
And then do a calibrate
Open
Short
load.
Now it is supposedly calibrated for anywhere between 3 and 30 Mhz correct?
Now I look at the who range and decide to zoom in on say 7 to 7.3
Start 7 Mhz
stop 7.3 Mhz
is it still calibrated?
How about really narrow like 7050 to 7060 Khz
still calibrated?
Joe WB9SBD
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Joe,. The Nano has discreet frequency steps you can set. Since you have an H4, you can have up to 401 steps between the lowest and highest swept frequencies.?
You need to keep this in mind as everything between the steps is interpolated.?
On Tue., 21 Sep. 2021 at 7:28 p.m., Joe WB9SBD<nss@...> wrote: Thanks, I was thinking of something like that.
Joe WB9SBD
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On 9/21/2021 6:12 PM, alan victor wrote: Always calibrated however, unit does interpolation. Therefore, if you desire best accuracy over a given range, then cal over THAT range.
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Joe, Another good way to learn about the NanoVNA is to read old posts in this group. Many typical questions have already been answered. For example this post which deals with your question. /g/nanovna-users/topic/73210908#12819Roger
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On Tue, Sep 21, 2021 at 04:03 PM, Joe WB9SBD wrote: is it still calibrated?
How about really narrow like 7050 to 7060 Khz
still calibrated?
Joe WB9SBD
Joe, The best way to learn about your NanoVNA is to "learn by doing". Calibrate your unit for 3 to 30 MHz. and make a measurement of a narrow band like 40M by zooming in. Then calibrate for just the 40m band and make a measurement. Then compare the two and see how different they are. This is a great way to become proficient with the NanoVNA. Roger
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Thanks, I was thinking of something like that.
Joe WB9SBD
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On 9/21/2021 6:12 PM, alan victor wrote: Always calibrated however, unit does interpolation. Therefore, if you desire best accuracy over a given range, then cal over THAT range.
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Always calibrated however, unit does interpolation. Therefore, if you desire best accuracy over a given range, then cal over THAT range.
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Ok,
say I set up Stimulus for 3 to 30 Mhz.
And then do a calibrate
Open
Short
load.
Now it is supposedly calibrated for anywhere between 3 and 30 Mhz correct?
Now I look at the who range and decide to zoom in on say 7 to 7.3
Start 7 Mhz
stop 7.3 Mhz
is it still calibrated?
How about really narrow like 7050 to 7060 Khz
still calibrated?
Joe WB9SBD
|
OK, that's adjustable for different jacket/braid/dielectric/center diameters, do you have to swap the cartridge for different strip lengths?
73, Willie N1JBJ
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On Sep 21, 2021, at 4:58 PM, Jim Lux <jim@...> wrote:
On 9/21/21 1:20 PM, William Smith wrote:
Hey Jim,
Do you have a pointer to the fancy adjustable one? I've been having a hard time finding anything other than 2 and 3 blade non-adjustable ones
73, Willie N1JBJ Paladin CST Pro
looks like it
On Sep 21, 2021, at 2:56 PM, Jim Lux <jim@...> wrote:
the fancy adjustable one
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On 9/21/21 1:20 PM, William Smith wrote: Hey Jim,
Do you have a pointer to the fancy adjustable one? I've been having a hard time finding anything other than 2 and 3 blade non-adjustable ones
73, Willie N1JBJ Paladin CST Pro looks like it On Sep 21, 2021, at 2:56 PM, Jim Lux <jim@...> wrote:
the fancy adjustable one
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RandMental
Mike C.
Roger Need