Re: Testing a monolitic band filter (3 pins)
hello
I tested with the nanovna several filters 45Mhz type 45R15AZ. Respond is better than Motorola 20J26.
The measurement is consistent with several filters and gives substantially the same result.
How is the black point defined on this type of filter if you want to pair 2 to make a 4-pole filter.
for exemple my measurement:
pin"1" TX(nano)-- pin2"Gnd"-- " pin3"RX (nano) all filters positioned in the same direction
so for a 4 poles filter
13--13 -- >the best i think ?
31--31
13--31
31--13
cdt
cdt
|
Thanks Bob!
Op vr 6 mei 2022 om 02:11 schreef Bob Ecclestone VK2ZRE <
becclest@...>:
toggle quoted message
Show quoted text
Hello Victor,
I am sure you will get flooded with replies to your question.
The answer is simple, early versions of the nVNA had a nominal Port1
output of -13dBm, later versions had redesigned Port 1/bridge circuitry
and the nominal output is now +1dBm.
So your unit measures pretty close to (a very loose) specification for a
later design of the NanoVNA.
73...Bob VK2ZRE
On 6/05/2022 8:29 am, Victor Reijs wrote:
Hello all of you,
I am trying to find some authoritative info on the output power of the
NanoVNA.
In several links I see -13dBm (and sometimes even increasing with
frequency: or
).
Anyway -13dBm is not much: some .005mW (
).
So I checked with a scope and did a start-stop from 7MHz to 7.1MHz, and I
see a block function with amplitude of 0.56V (unloaded). When I load with
50ohm load I get 0.28V.
The amplitude of the fundamental freq. of a block is 0.28*4/pi(). And to
get the Vrms value, we divided it with sqrt(2):
0.28*4/pi()/1.4 = 0.25 Vrms
That makes 1.3mW (0.25^2/50) or 1.1 dBm (10*log(1.1mW/1mW))
So where is this -13 dBm coming from?
Can you help?
All the best,
Victor
|
Re: Uncertain about coax loss reading
I don't think the 2-port thru measurement will be any more accurate for
simple cable measurements. The nano is very accurate with a good dynamic
range on reflected (s11) measurements. If the loss were very high, e.g.
greater than 30dB, then the thru measurement may be more accurate, because
the two-way loss measured by s11 would be >60dB, coming closer to the
dynamic range limits.
toggle quoted message
Show quoted text
On Thu, May 5, 2022, 8:08 PM kosmos <cosmo.pcs@...> wrote: Oh that's an awesome feature I didn't even know about, thank you! Though
I'm still going to troubleshoot to try and get the other port to work
properly.
Is this calculated value as accurate as having it plugged in both though?
I would assume it's a little more accurate when it is.
|
Re: Uncertain about coax loss reading
Oh that's an awesome feature I didn't even know about, thank you! Though I'm still going to troubleshoot to try and get the other port to work properly.
Is this calculated value as accurate as having it plugged in both though? I would assume it's a little more accurate when it is.
|
Re: Uncertain about coax loss reading
An easier way to check coax loss is available on the H4 with most recent firmware. You connect the coax to only the s11 port, and leave the far end of the coax open. Then from the menu choose measure / coax. The measurements will appear at the left of the screen, including a loss measurement at whatever frequency the cursor is at. So you set the frequency range to include the frequency of interest, and directly read the loss at that freq. The nano makes this measurement from the s11 reflected wave, and divides by 2 because the raw measurement is for both up and back along the cable. It's a nice feature. Not also that the frequency range must include a low enough frequency to be a quarter wavelength for the length of the cable, so I often just calibrate for 50kHz - 30MHz when doing this type of measure so I don't have to think of it. Even with this wide range it gives good accuracy because the nano firmware does a good job of interpolation between measurement points (thank you, Hugen!). (Note that the length measurement shown depends entirely on the accuracy of the velocity factor - so be careful with that value.) On Thu, May 5, 2022, 5:48 PM Bob Ecclestone VK2ZRE <becclest@...> wrote: don't think it is busted. Your photo shows the port unterminated. Try
terminating both ports in 50 Ohms and rerun the scan.
The Port2 input is pretty sensitive to internal crosstalk (noise), so I
would not be too concerned.
Remember, this is a ~$100 instrument. It performs exceptionally well for
that amount of money:-)
73...Bob VK2ZRE
On 6/05/2022 10:36 am, kosmos wrote:
Very cool tip, thanks for detailing it!
It removed the movement, but it's still not a line, still looks like noise with inaccurate values unfortunately.
Could the S21 port just be busted?
|
Re: Uncertain about coax loss reading
don't think it is busted. Your photo shows the port unterminated. Try terminating both ports in 50 Ohms and rerun the scan.
The Port2 input is pretty sensitive to internal crosstalk (noise), so I would not be too concerned.
Remember, this is a ~$100 instrument. It performs exceptionally well for that amount of money:-)
73...Bob VK2ZRE
toggle quoted message
Show quoted text
On 6/05/2022 10:36 am, kosmos wrote: Very cool tip, thanks for detailing it!
It removed the movement, but it's still not a line, still looks like noise with inaccurate values unfortunately.
Could the S21 port just be busted?
|
Re: Uncertain about coax loss reading
Very cool tip, thanks for detailing it!
It removed the movement, but it's still not a line, still looks like noise with inaccurate values unfortunately.
Could the S21 port just be busted?
|
Re: Uncertain about coax loss reading
Hello,
Try setting the THRESHOLD setting to 280 and do another complete calibration.
Some clock chips are not stable at the default value of 300(MHz). These chips are severely overclocked in the NanoVNA design, their nominal Fmax is 200MHz.
The instability shows up as "noise" in many traces.
This will reduce your "maximum" frequency to 1400MHz using the 5th harmonic, but most manufacturers state a useful maximum up to about 1250MHz anyway.
Make sure you do a RESET and CLEAR ALL to clear all old Calibration data before you do the new cal.
HTH.
73...Bob VK2ZRE
toggle quoted message
Show quoted text
On 6/05/2022 3:03 am, kosmos wrote: This is when I calibrated and left the cable in through, used the thin coax that comes with it.
|
Hello Victor,
I am sure you will get flooded with replies to your question.
The answer is simple, early versions of the nVNA had a nominal Port1 output of -13dBm, later versions had redesigned Port 1/bridge circuitry and the nominal output is now +1dBm.
So your unit measures pretty close to (a very loose) specification for a later design of the NanoVNA.
73...Bob VK2ZRE
toggle quoted message
Show quoted text
On 6/05/2022 8:29 am, Victor Reijs wrote: Hello all of you,
I am trying to find some authoritative info on the output power of the
NanoVNA.
In several links I see -13dBm (and sometimes even increasing with
frequency: or
).
Anyway -13dBm is not much: some .005mW (
).
So I checked with a scope and did a start-stop from 7MHz to 7.1MHz, and I
see a block function with amplitude of 0.56V (unloaded). When I load with
50ohm load I get 0.28V.
The amplitude of the fundamental freq. of a block is 0.28*4/pi(). And to
get the Vrms value, we divided it with sqrt(2):
0.28*4/pi()/1.4 = 0.25 Vrms
That makes 1.3mW (0.25^2/50) or 1.1 dBm (10*log(1.1mW/1mW))
So where is this -13 dBm coming from?
Can you help?
All the best,
Victor
|
Hello all of you,
I am trying to find some authoritative info on the output power of the
NanoVNA.
In several links I see -13dBm (and sometimes even increasing with
frequency: or
).
Anyway -13dBm is not much: some .005mW (
).
So I checked with a scope and did a start-stop from 7MHz to 7.1MHz, and I
see a block function with amplitude of 0.56V (unloaded). When I load with
50ohm load I get 0.28V.
The amplitude of the fundamental freq. of a block is 0.28*4/pi(). And to
get the Vrms value, we divided it with sqrt(2):
0.28*4/pi()/1.4 = 0.25 Vrms
That makes 1.3mW (0.25^2/50) or 1.1 dBm (10*log(1.1mW/1mW))
So where is this -13 dBm coming from?
Can you help?
All the best,
Victor
|
Re: Two 1/4 wavelength transformers for one antenna and two RX-radios. Help my thinking
Hi Torbj?rn,
going back to your coax xable splitter:
When you have a signal source at A and two loads connected to B and C, the circuit works fine, because each 75? cable will transform its 50? load into 112.5?, and the two 112.5? inputs in parallel give 56.25?, close enough to the 50? the source expects.
When you have two phase-synchronous signal sources at B and C, the same will happen in reverse, and the circuit will work fine too.
But when you have a source at B, and loads at A and C, it will not work. The load at C will be transformed to 112.5? by that cable, this will appear in parallel with the load at A, giving 34.6?, and this will be transformed to 162.5? by the other cable.
Very simply said, your circuit isn't 3-way-symmetric. Ports B and C are identical and interchangeable, but port A is different. You always need to have either the source or the load on port A, and put identical things on B and C - two loads or two synchronized sources.
Manfred
|
Re: Uncertain about coax loss reading
This is when I calibrated and left the cable in through, used the thin coax that comes with it.
|
Re: Uncertain about coax loss reading
The value for S11 looks "about" right. Yes, S21 is noisy. Run the same
test with the coax you used for the through cal, of course, after another
complete cal.
Dave - W?LEV
toggle quoted message
Show quoted text
On Thu, May 5, 2022 at 4:38 PM kosmos <cosmo.pcs@...> wrote: Here's with a reset calibration, I don't think S21 should be noisy like
that, should it?
-- *Dave - W?LEV* *Just Let Darwin Work*
--
Dave - W?LEV
|
Re: Uncertain about coax loss reading
Here's with a reset calibration, I don't think S21 should be noisy like that, should it?
|
Re: Two 1/4 wavelength transformers for one antenna and two RX-radios. Help my thinking
On Wed, May 4, 2022 at 08:36 AM, KENT BRITAIN wrote:
The TV splitters to connect two TV's to the same antenna are very cheap and
work just fine at that frequency.? ? They are a simple transformer, they
have no impedance of their own.? So splitting 75 Ohms or 50 Ohms is no
difference.? ? Don't like the PAL or F connectors, take out the little
transformer and put it in your own box.? Kent
I tested a quality CATV splitter and found it worked quite well for 50 ohm applications. The Return Loss, S21 and Isolation graphs obtained using a NanoVNA are attached. I used F to BNC adapters (from Amazon) for these tests. Roger
|
Uncertain about coax loss reading
Still new to using a VNA.
I've calibrated my NanoVNA-H4 and double checked the calibration with the 3 tips once again as per hexandflex' guide, with the isolation and through, since I want to measure the coax loss.
So far so good.
Now when I plug in the cable to both S11 and S21, I get some really odd readings that don't seem to match up with what I'm seeing in guides and videos. My logmag is all over the place and nowhere near showing a proper reading.
What is it that I'm missing here? Did I do something wrong?
|
Re: Two 1/4 wavelength transformers for one antenna and two RX-radios. Help my thinking
Regarding power splitters/combiners, check out the Gysel (rhymes with Diesel) combiner; its termination resistors are 50¦¸ and grounded, much easier to deal with than the floating 100¦¸ resistor of the Wilkinson type, especially when it comes to high power work.
73, Don N2VGU
|
Re: Two 1/4 wavelength transformers for one antenna and two RX-radios. Help my thinking
Thanks Andy and Kent. Using the Wilkinson approach my splitter gives SWR 1.1 at the design frequency, quite broad. The input from Kent gave me the idea to make a splitter using two ferrite-toroidal transformers, winding prim/sek 5/7 turns would give the correct transformation, root of 2. Then I could place the transformers in a box together with three ccoax connectors. I will experiment with this setup.
73/Torbjorn
|
Re: Two 1/4 wavelength transformers for one antenna and two RX-radios. Help my thinking
On 2022-05-04 17:39:+0100, you wrote:
You're missing the resistor.
73 Andy, G4KNO
Very useful link. Thanks! ~R~ 72/73 de Rich NE1EE The Dusty Key On the banks of the Piscataqua
|
Re: Two 1/4 wavelength transformers for one antenna and two RX-radios. Help my thinking
You're missing the resistor. 73 Andy, G4KNO. On Wed, May 4, 2022 at 4:07 PM Torbj?rn Toreson <torbjorn.toreson@...> wrote: Hello,
I intend to use the same antenna for two RX-radios. I will lose 3 dB, but
for the sake of the radios RX-input I intended to present each with roughly
50 ohms.
The frequency is about 90 MHz (not HAM-use). I made two 1/4 wave
transformers with RG59 coax, taking VF of 0,66 in consideration. Measuring
each one with the Nano and 50 on the outer side I get as anticipated about
110 ohm. Now the idea is to parallell the two 110 ohm sides and get around
55 ohm, this is where the antenna should be connected. Imagine the
cable-setup as a V, with the vertex (bottom on the V) labeled A and the two
upper parts labeled B and C.
When I connect 50 ohm dummies to B and C then I can measure about 50 ohm
at A for 90 MHz. Now I wanted to see what one of the radios would feel so I
connected 50 ohm dummies (actually 50 ohm pieces from calibration kits) at
A and C. Now measuring at B I was expecting to see about 50 ohm. That was
not the case, the result was about 140 ohm (X about 0) and SWR about 3 (of
course). At about 150 MHz I got a SWR minimum.
Please help me to understand why the setup works one way (as e.g. to
connect two phased antennas) but not the other way to connect one antenna
to two radios.
73/Torbjorn/SM6AYM
|
Gerard
kosmos
Roger Need
Donald S Brant Jr
Rich NE1EE