|
I doubt it, since measuring at the equipment¡¯s antenna port you¡¯re measuring the circuitry inside and there¡¯s no telling what the ¡®results¡¯ will be. But you¡¯ve nailed down how to test measuring for a specific impedance; any simple non-inductive resistance will work. Same principle for testing ununs / baluns / any impedance matching network.
Have fun!!!
"Silence is golden. Duct tape is silver."
toggle quoted message
Show quoted text
On Jan 9, 2022, at 16:30, Jeff Green <Jeff.L.Green1970@...> wrote:
?The Backstory:
The company I work for has been merged via hostile takeover with a nother company and most of the employees are being laid off or offered early retirement. A coworker is relocating to a company in Texas, cleaning out and gave me a year old, unused, Nooelec NanoVNA - Open Hardware Vector Network Analyzer Kit.
The Analyzer kit included SOLT calibration kit.
I downloaded NanoVNASaver.x64 from
I've played with the hardware and software enough to be passably familiar with the process, I used a 75 ohm CATV terminator to produce a 1.5:1 mismatch and the results were what I expected.
Goal:
Given my hardware, software, and less then stellar knowledge and skill set, is it practical to measure the actual antenna input port impedance of several general coverage receivers?
I tried using the search function to see if anyone has already tried this.
Thank you
Jeff
|
Check out W2AEW testing the input of an amp. with a nano: Hope this helps. Richard, K8CYK On Sun, Jan 9, 2022, 3:41 PM Jeff Green <Jeff.L.Green1970@...> wrote: Thank you, I was afraid of that.
-------------------
From:
On page 61: "Splitting up the winding into two rings suitably spaced
provided a reasonable compromise between simplicity of construction and
constancy of antenna input impedance. However, instead of 125 ohm ¡À15% the
impedance actually varies from 50 - 300 ohms."
-------------------
So, Any idea how the input impedance is measured and how did Collins
verify the above data?
Thank you.
|
On 1/9/22 12:51 PM, Jeff Green wrote: The Backstory:
The company I work for has been merged via hostile takeover with a nother company and most of the employees are being laid off or offered early retirement. A coworker is relocating to a company in Texas, cleaning out and gave me a year old, unused, Nooelec NanoVNA - Open Hardware Vector Network Analyzer Kit.
The Analyzer kit included SOLT calibration kit.
I downloaded NanoVNASaver.x64 from
I've played with the hardware and software enough to be passably familiar with the process, I used a 75 ohm CATV terminator to produce a 1.5:1 mismatch and the results were what I expected.
Goal:
Given my hardware, software, and less then stellar knowledge and skill set, is it practical to measure the actual antenna input port impedance of several general coverage receivers? It should work ok, but make sure your receiver can tolerate the input power? from CH0.
|
On Sun, Jan 9, 2022 at 01:30 PM, Jeff Green wrote:
Goal:
Given my hardware, software, and less then stellar knowledge and skill set, is
it practical to measure the actual antenna input port impedance of several
general coverage receivers?
Jeff, Yes you can measure the input impedance of an HF receiver with your NanoVNA but you need to be careful you do not overload the front end. The output of the NanoVNA is around 0 dBm which is too high. The trick is to lower the NanoVNA output power as much as possible. If you have recent firmware by DiSlord you can set the power level to 2 ma. (which is the lowest possible) but still too high. The next step is to add a 20 dB attenuator to the S11 port and then calibrate with the attenuator in place. The attenuator will lower the signal into the receiver and reduce the dynamic range but you can still get reasonable SWR and RL measurements. The impedance measurement will be reasonable as well if close to 50 ohms. The further away from 50 ohms the worse the accuracy. You will notice that the impedance will change rapidly when you are outside the passband of the receiver front end filters. Roger
|
On 1/9/22 2:40 PM, Jeff Green wrote: Thank you, I was afraid of that.
-------------------
From:
On page 61: "Splitting up the winding into two rings suitably spaced provided a reasonable compromise between simplicity of construction and constancy of antenna input impedance. However, instead of 125 ohm ¡À15% the impedance actually varies from 50 - 300 ohms."
-------------------
So, Any idea how the input impedance is measured and how did Collins verify the above data?
Thank you. You'd measure it (today) with a VNA, making sure that you pick a drive level that's reasonable for the receiver (i.e. if your receiver input can only tolerate -50dBm, then better not put -10 dBm in). The trick is that active devices often have impedances that vary with operating point. Let's assume you know the gain of your receiver very accurately. That is, you've turned off any AGC, and you can measure the output for a given input level.? Then, you can put known impedances in series with the input, forming a voltage divider (Zrcv/(Zrcv + Zseries)), and from a set of measurements, you can determine what Zrcv is. You will need both resistive and reactive series Z, because typically, you can only measure the magnitude of the signal, not the phase.
|
You cannot just put an arbitrarily-large attenuation after a VNA port and expect reasonable results. Roger Need's suggestion of 20dB is about as high as I would go; keep in mind that the round-trip loss is double the attenuation so the signal quickly becomes uselessly noisy.
And, yes, you can use a noise bridge, BITD there were some high-end ones made commercially.
Best regards.
|
During Kenwood transceiver bench alignments, they specify 100dBuVEMF as the S9+20 outer marker. This equates to -1dBm. As an anecdote, during a contest with multi-transmitters, we saw around 3Volts of RF at one receiver (tuned to a different band of course), and it survived quite happily. Best I can make out, the NanoVNA only outputs like -10dBm.. ??
|
Input regarding Kenwood S-Meters. I have and have rigorously measured the
S-Meter input power vs. S-meter indication. It's off the wall for that
radio, if there were a wall!! At some points below S-9, as little as 1 dBm
difference produces an additional S-Unit increase/decrease. S-9 is no
where near -73 dBm. However, above S-9, it's not bad for every 10 dB
increase in input power. If it's not a modern SDR, the S-Meter doesn't
mean squat - even the Collins S-Line!!!!!!
With S-9 at -73 dBm, that would be +34 dBuV in a non-reactive 50-ohm
system. 20 over S-9 would be 40 dB (voltage) over that or +74 dBuV. To be
rigorous, the given value of 100 eBuV is incorrect to be rigorous. What's
more, what does Kenwood mean by "dBuVEMF"??? What the dickens does the
added "EMF" refer to????
Dave - W?LEV
toggle quoted message
Show quoted text
On Wed, Feb 9, 2022 at 5:25 AM VK2CZ DAVID <16240244c1@...> wrote: During Kenwood transceiver bench alignments, they specify 100dBuVEMF as
the S9+20 outer marker. This equates to -1dBm. As an anecdote, during a
contest with multi-transmitters, we saw around 3Volts of RF at one receiver
(tuned to a different band of course), and it survived quite happily. Best
I can make out, the NanoVNA only outputs like -10dBm.. ??
--
*Dave - W?LEV*
*Just Let Darwin Work*
|
I believe it. My very old (now) Icom 2100 single band VHF radio is even worse. I've seen the meter go from S1 to S9 with only a 6 to 7 db increase in power from the other end! Just asking, is it really that hard to measure signal strength with even the least bit of accuracy in a radio? Or it they just didn't try?
Max KG4PID
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Show quoted text
On Wednesday, February 9, 2022, 07:36:03 PM CST, W0LEV <davearea51a@...> wrote: Input regarding Kenwood S-Meters.? I have and have rigorously measured the S-Meter input power vs. S-meter indication.? It's off the wall for that radio, if there were a wall!!? At some points below S-9, as little as 1 dBm difference produces an additional S-Unit increase/decrease.? S-9 is no where near -73 dBm.? However, above S-9, it's not bad for every 10 dB increase in input power.? If it's not a modern SDR, the S-Meter doesn't mean squat - even the Collins S-Line!!!!!! With S-9 at -73 dBm, that would be +34 dBuV in a non-reactive 50-ohm system.? 20 over S-9 would be 40 dB (voltage) over that or +74 dBuV.? To be rigorous, the given value of 100 eBuV is incorrect to be rigorous.? What's more, what does Kenwood mean by "dBuVEMF"???? What the dickens does the added "EMF" refer to???? Dave - W?LEV On Wed, Feb 9, 2022 at 5:25 AM VK2CZ DAVID <16240244c1@...> wrote: During Kenwood transceiver bench alignments, they specify 100dBuVEMF as
the S9+20 outer marker.? This equates to -1dBm.? As an anecdote, during a
contest with multi-transmitters, we saw around 3Volts of RF at one receiver
(tuned to a different band of course), and it survived quite happily.? Best
I can make out, the NanoVNA only outputs like -10dBm.. ??
-- *Dave - W?LEV* *Just Let Darwin Work*
|
Just lurking here, but does anyone actually look at an S meter while operating? Just kind of wondering. I'll admit I mostly do contests, so I'm way too busy to worry about the actual S meter reading. I would like it if they removed the S meter and put the front panel real estate to better use. Just me I guess. I used to work for HP/Agilent Microwave, and in that case we worried about 0.01dB in measurements. But on HF if someone actually asks how loud they are I just kinda take a WAG at it. If you are louder than the noise I can hear you, so no problem. I guess we all have our different interests! Oh and yes, I do own a Nano-VNA. Real early one, works great for antenna projects and filters. I did have three HP VNAs before our big fire here, but they went up in smoke with everything else. But the Nano is way easier to move around. Plenty good enough for HF stuff. Ken K6MR ________________________________ From: [email protected] < [email protected]> on behalf of Max via groups.io <kg4pid@...> Sent: Wednesday, February 9, 2022 6:05 PM To: [email protected] < [email protected]> Subject: Re: [nanovna-users] Using NanoVNA to measure receive antenna port impedance #measurement I believe it. My very old (now) Icom 2100 single band VHF radio is even worse. I've seen the meter go from S1 to S9 with only a 6 to 7 db increase in power from the other end! Just asking, is it really that hard to measure signal strength with even the least bit of accuracy in a radio? Or it they just didn't try? Max KG4PID On Wednesday, February 9, 2022, 07:36:03 PM CST, W0LEV <davearea51a@...> wrote: Input regarding Kenwood S-Meters. I have and have rigorously measured the S-Meter input power vs. S-meter indication. It's off the wall for that radio, if there were a wall!! At some points below S-9, as little as 1 dBm difference produces an additional S-Unit increase/decrease. S-9 is no where near -73 dBm. However, above S-9, it's not bad for every 10 dB increase in input power. If it's not a modern SDR, the S-Meter doesn't mean squat - even the Collins S-Line!!!!!! With S-9 at -73 dBm, that would be +34 dBuV in a non-reactive 50-ohm system. 20 over S-9 would be 40 dB (voltage) over that or +74 dBuV. To be rigorous, the given value of 100 eBuV is incorrect to be rigorous. What's more, what does Kenwood mean by "dBuVEMF"??? What the dickens does the added "EMF" refer to???? Dave - W?LEV On Wed, Feb 9, 2022 at 5:25 AM VK2CZ DAVID <16240244c1@...> wrote: During Kenwood transceiver bench alignments, they specify 100dBuVEMF as
the S9+20 outer marker. This equates to -1dBm. As an anecdote, during a
contest with multi-transmitters, we saw around 3Volts of RF at one receiver
(tuned to a different band of course), and it survived quite happily. Best
I can make out, the NanoVNA only outputs like -10dBm.. ??
-- *Dave - W?LEV* *Just Let Darwin Work*
|
Dave,
Slight gaffe on my part... the 100dBuVemf is to calibrate the 60dB over 9 S meter full scale on all Kenwood Transceivers..
The dBuVemf is the kirchoff voltage source for sig generators with 50 ohm output impedances connected to a 50ohm load. It's a painful unit to deal on all but the professional sig generators, ie snapshot of my E4438C Amplitude setting screen..
|
Coming back on the title, how to measure...
I wrote an article about that a couple of months ago, measuring the input impedance of a Elecraft K3 receiver.
It was published in the SARC Communicator sept- Oct 2021. This is the link:
See page 43
73,
Arie PA3A
|
Hi Arie, read your article with great interest. I understand my nanoVNA, I think, and I understand complex algebra and Z = R + jX. But I get VERY confused by standard radio or ham talk. I made a crystal radio over the past 2 years, and never understood why or how it would be 50 ohms. I always wanted to measure my Z, but I think the main thing the antenna signal is ¡°looking at¡± is my diode, since my tank circuit has near-infinite resistance and thus is almost an open circuit. Are you suggesting I can simply plug my nanoVNA in where my antenna usually goes and get a receiver input impedance? Also, you spent a bunch of time on an attenuator, but later (I think) you concluded you didn¡¯t need it. Why would I want one? Any other suggestions for a naive beginner? I am thinking about matching Z from antenna to receiver, but I can¡¯t measure either, and when I guess at values and then design a little LC circuit to match impedances, I find it will resonate at darn near my target f, sending my desired signal to ground!
Andy
toggle quoted message
Show quoted text
On Feb 10, 2022, at 5:43 AM, Arie Kleingeld PA3A <pa3a@...> wrote:
Coming back on the title, how to measure...
I wrote an article about that a couple of months ago, measuring the input impedance of a Elecraft K3 receiver.
It was published in the SARC Communicator sept- Oct 2021. This is the link:
See page 43
73,
Arie PA3A
|
They don't try. It's that simple. I've measured only one "vintage" radio of some 30 that put S-9 close to -73 dBm. That was the Swan 100MX. Of course, the rest of the S-Meter response is wonkered as is the Kenwood TS-2000. The ability to indicate proper S-Units vs. input power has been around since cell phones. There is an 80 dB dynamic range requirement to properly measure the received strength for cell phones to properly operate. It's the RSS output from the "IF" chip, or equivalent. This could have easily been incorporated into our radios long....long ago, but they didn't. Today, with the SDR receivers, it's a no-brainer and they are pretty accurate (at least for my Icom 7300, 7610, Airspys, and RSP). Dave - W?LEV On Thu, Feb 10, 2022 at 2:06 AM Max via groups.io <kg4pid= [email protected]> wrote: I believe it. My very old (now) Icom 2100 single band VHF radio is even
worse. I've seen the meter go from S1 to S9 with only a 6 to 7 db increase
in power from the other end! Just asking, is it really that hard to measure
signal strength with even the least bit of accuracy in a radio? Or it they
just didn't try?
Max KG4PID
On Wednesday, February 9, 2022, 07:36:03 PM CST, W0LEV <
davearea51a@...> wrote:
Input regarding Kenwood S-Meters. I have and have rigorously measured the
S-Meter input power vs. S-meter indication. It's off the wall for that
radio, if there were a wall!! At some points below S-9, as little as 1 dBm
difference produces an additional S-Unit increase/decrease. S-9 is no
where near -73 dBm. However, above S-9, it's not bad for every 10 dB
increase in input power. If it's not a modern SDR, the S-Meter doesn't
mean squat - even the Collins S-Line!!!!!!
With S-9 at -73 dBm, that would be +34 dBuV in a non-reactive 50-ohm
system. 20 over S-9 would be 40 dB (voltage) over that or +74 dBuV. To be
rigorous, the given value of 100 eBuV is incorrect to be rigorous. What's
more, what does Kenwood mean by "dBuVEMF"??? What the dickens does the
added "EMF" refer to????
Dave - W?LEV
On Wed, Feb 9, 2022 at 5:25 AM VK2CZ DAVID <16240244c1@...> wrote:
During Kenwood transceiver bench alignments, they specify 100dBuVEMF as
the S9+20 outer marker. This equates to -1dBm. As an anecdote, during a
contest with multi-transmitters, we saw around 3Volts of RF at one receiver
(tuned to a different band of course), and it survived quite happily. Best
I can make out, the NanoVNA only outputs like -10dBm.. ??
--
*Dave - W?LEV*
*Just Let Darwin Work*
-- *Dave - W?LEV* *Just Let Darwin Work*
|
Hi Dave
And that port is designed to look at a 50 Ohm load, not look like a 50 Ohm load!
Sweeping the front end of most radios just gives you an idea of their preseclection.? ? ?Kent WA5VJB
toggle quoted message
Show quoted text
On Thursday, February 10, 2022, 10:51:56 AM CST, W0LEV <davearea51a@...> wrote: They don't try.? It's that simple.? I've measured only one "vintage" radio of some 30 that put S-9 close to -73 dBm.? That was the Swan 100MX.? Of course, the rest of the S-Meter response is wonkered as is the Kenwood TS-2000. The ability to indicate proper S-Units vs. input power has been around since cell phones.? There is an 80 dB dynamic range requirement to properly measure the received strength for cell phones to properly operate.? It's the RSS output from the "IF" chip, or equivalent.? This could have easily been incorporated into our radios long....long ago, but they didn't. Today, with the SDR receivers, it's a no-brainer and they are pretty accurate (at least for my Icom 7300, 7610, Airspys, and RSP). Dave - W?LEV On Thu, Feb 10, 2022 at 2:06 AM Max via groups.io <kg4pid= [email protected]> wrote: ? I believe it. My very old (now) Icom 2100 single band VHF radio is even
worse. I've seen the meter go from S1 to S9 with only a 6 to 7 db increase
in power from the other end! Just asking, is it really that hard to measure
signal strength with even the least bit of accuracy in a radio? Or it they
just didn't try?
Max KG4PID
? On Wednesday, February 9, 2022, 07:36:03 PM CST, W0LEV <
davearea51a@...> wrote:
? Input regarding Kenwood S-Meters.? I have and have rigorously measured the
S-Meter input power vs. S-meter indication.? It's off the wall for that
radio, if there were a wall!!? At some points below S-9, as little as 1 dBm
difference produces an additional S-Unit increase/decrease.? S-9 is no
where near -73 dBm.? However, above S-9, it's not bad for every 10 dB
increase in input power.? If it's not a modern SDR, the S-Meter doesn't
mean squat - even the Collins S-Line!!!!!!
With S-9 at -73 dBm, that would be +34 dBuV in a non-reactive 50-ohm
system.? 20 over S-9 would be 40 dB (voltage) over that or +74 dBuV.? To be
rigorous, the given value of 100 eBuV is incorrect to be rigorous.? What's
more, what does Kenwood mean by "dBuVEMF"???? What the dickens does the
added "EMF" refer to????
Dave - W?LEV
On Wed, Feb 9, 2022 at 5:25 AM VK2CZ DAVID <16240244c1@...> wrote:
During Kenwood transceiver bench alignments, they specify 100dBuVEMF as
the S9+20 outer marker.? This equates to -1dBm.? As an anecdote, during a
contest with multi-transmitters, we saw around 3Volts of RF at one receiver
(tuned to a different band of course), and it survived quite happily. Best
I can make out, the NanoVNA only outputs like -10dBm.. ??
--
*Dave - W?LEV*
*Just Let Darwin Work*
-- *Dave - W?LEV* *Just Let Darwin Work*
|
Hi Andy,
I understand that you are talking about a crystal radio being an LC-circuit, a diode plus capacitor and a headset?
You could measure the imput impedance of that receiver. Thing is that a strong signal of a VNA could drive the diode that it would take current. Then the VNA probably will see another impedance that when the diode was not conducting.
That is what the article was about and why I made that simple attenuators to prevent that. And also wanted to test how well? my nanoVNA would cope with that.
Those simple crystal receivers usually are used in MF-range, well I did once in a while. The antenna ( most times a piece of wire) will have a pretty high impedance (resistance and also capacitive reactance) if you measure it. The input impedance of the receiver will be far off 50 ohms so thinking about 50 ohms -matching procedures is not the way to go.
Tapping the antennawire into the coil (directly of via a coupled loop) and tuning the C of the LC circuit is the way I would choose and see what happens. If you hear a lot of bandnoise when you connect the antenna and you can hear the stations you expect, you are on the right path.
That article by the way was one in a series of seven. English versions were all published in the Communicator.
73,
Arie PA3A
Op 10-2-2022 om 15:14 schreef Andrew Kurtz via groups.io:
toggle quoted message
Show quoted text
Hi Arie, read your article with great interest. I understand my nanoVNA, I think, and I understand complex algebra and Z = R + jX. But I get VERY confused by standard radio or ham talk. I made a crystal radio over the past 2 years, and never understood why or how it would be 50 ohms. I always wanted to measure my Z, but I think the main thing the antenna signal is ¡°looking at¡± is my diode, since my tank circuit has near-infinite resistance and thus is almost an open circuit. Are you suggesting I can simply plug my nanoVNA in where my antenna usually goes and get a receiver input impedance? Also, you spent a bunch of time on an attenuator, but later (I think) you concluded you didn¡¯t need it. Why would I want one? Any other suggestions for a naive beginner? I am thinking about matching Z from antenna to receiver, but I can¡¯t measure either, and when I guess at values and then design a little LC circuit to match impedances, I find it will resonate at darn near my target f, sending my desired signal to ground!
Andy
On Feb 10, 2022, at 5:43 AM, Arie Kleingeld PA3A<pa3a@...> wrote:
Coming back on the title, how to measure...
I wrote an article about that a couple of months ago, measuring the input impedance of a Elecraft K3 receiver.
It was published in the SARC Communicator sept- Oct 2021. This is the link:
See page 43
73,
Arie PA3A
|
Unless you live in an extremely RFI prone and RFI polluted area, you won't
hear "antenna noise" on a crystal set.
Further, the crystal set runs on voltage so the high-Z antenna is quite
appropriate, but not for the 50-ohm system of the NANOs.
The one I finally built a decade or so ago for fun, used taps on the
primary coil of the LC tuned network for the detector. That enables
adjustment of the trade-off between recovered audio and selectivity (tuned
Q). I coupled the antenna to the main coil of the LC network through a
much smaller (inductance) coil to allow best selectivity of the main
inductor. Here in N. Colorado in the evening when the D-Layer dissolves,
I've detected as many and separated up to 23 stations using a 480-foot long
doublet. That's in the presence of our nemesis blowtorch at 760 kHz out of
Boulder which at times measures as much as -30 dBm into 50-ohms (spectrum
analuzer).
To better understand resonance, I believe everyone starting in ham radio
should build his/her own crystal radio. It's an excellent
teaching/learning tool!
Dave - W?LEV
toggle quoted message
Show quoted text
On Thu, Feb 10, 2022 at 7:01 PM Arie Kleingeld PA3A <pa3a@...> wrote: Hi Andy,
I understand that you are talking about a crystal radio being an
LC-circuit, a diode plus capacitor and a headset?
You could measure the imput impedance of that receiver. Thing is that a
strong signal of a VNA could drive the diode that it would take current.
Then the VNA probably will see another impedance that when the diode was
not conducting.
That is what the article was about and why I made that simple
attenuators to prevent that. And also wanted to test how well my
nanoVNA would cope with that.
Those simple crystal receivers usually are used in MF-range, well I did
once in a while. The antenna ( most times a piece of wire) will have a
pretty high impedance (resistance and also capacitive reactance) if you
measure it. The input impedance of the receiver will be far off 50 ohms
so thinking about 50 ohms -matching procedures is not the way to go.
Tapping the antennawire into the coil (directly of via a coupled loop)
and tuning the C of the LC circuit is the way I would choose and see
what happens. If you hear a lot of bandnoise when you connect the
antenna and you can hear the stations you expect, you are on the right
path.
That article by the way was one in a series of seven. English versions
were all published in the Communicator.
73,
Arie PA3A
Op 10-2-2022 om 15:14 schreef Andrew Kurtz via groups.io:
Hi Arie, read your article with great interest. I understand my nanoVNA, I think, and I understand complex algebra and Z = R + jX. But I
get VERY confused by standard radio or ham talk. I made a crystal radio
over the past 2 years, and never understood why or how it would be 50
ohms. I always wanted to measure my Z, but I think the main thing the
antenna signal is ¡°looking at¡± is my diode, since my tank circuit has
near-infinite resistance and thus is almost an open circuit. Are you
suggesting I can simply plug my nanoVNA in where my antenna usually goes
and get a receiver input impedance? Also, you spent a bunch of time on an
attenuator, but later (I think) you concluded you didn¡¯t need it. Why would
I want one? Any other suggestions for a naive beginner? I am thinking
about matching Z from antenna to receiver, but I can¡¯t measure either, and
when I guess at values and then design a little LC circuit to match
impedances, I find it will resonate at darn near my target f, sending my
desired signal to ground!
Andy
On Feb 10, 2022, at 5:43 AM, Arie Kleingeld PA3A<pa3a@...>
wrote:
Coming back on the title, how to measure...
I wrote an article about that a couple of months ago, measuring the
input impedance of a Elecraft K3 receiver.
It was published in the SARC Communicator sept- Oct 2021. This is the
link:
See page 43
73,
Arie PA3A
--
*Dave - W?LEV*
*Just Let Darwin Work*
|
That was the situation when I tried that concept. Thunderstorms etc. :-)
Arie
Op 10-2-2022 om 21:32 schreef W0LEV:
toggle quoted message
Show quoted text
Unless you live in an extremely RFI prone and RFI polluted area, you won't
hear "antenna noise" on a crystal set.
|
Great, thanks!
toggle quoted message
Show quoted text
On Feb 10, 2022, at 2:01 PM, Arie Kleingeld PA3A <pa3a@...> wrote:
Hi Andy,
I understand that you are talking about a crystal radio being an LC-circuit, a diode plus capacitor and a headset?
You could measure the imput impedance of that receiver. Thing is that a strong signal of a VNA could drive the diode that it would take current. Then the VNA probably will see another impedance that when the diode was not conducting.
That is what the article was about and why I made that simple attenuators to prevent that. And also wanted to test how well my nanoVNA would cope with that.
Those simple crystal receivers usually are used in MF-range, well I did once in a while. The antenna ( most times a piece of wire) will have a pretty high impedance (resistance and also capacitive reactance) if you measure it. The input impedance of the receiver will be far off 50 ohms so thinking about 50 ohms -matching procedures is not the way to go.
Tapping the antennawire into the coil (directly of via a coupled loop) and tuning the C of the LC circuit is the way I would choose and see what happens. If you hear a lot of bandnoise when you connect the antenna and you can hear the stations you expect, you are on the right path.
That article by the way was one in a series of seven. English versions were all published in the Communicator.
73,
Arie PA3A
Op 10-2-2022 om 15:14 schreef Andrew Kurtz via groups.io:
Hi Arie, read your article with great interest. I understand my nanoVNA, I think, and I understand complex algebra and Z = R + jX. But I get VERY confused by standard radio or ham talk. I made a crystal radio over the past 2 years, and never understood why or how it would be 50 ohms. I always wanted to measure my Z, but I think the main thing the antenna signal is ¡°looking at¡± is my diode, since my tank circuit has near-infinite resistance and thus is almost an open circuit. Are you suggesting I can simply plug my nanoVNA in where my antenna usually goes and get a receiver input impedance? Also, you spent a bunch of time on an attenuator, but later (I think) you concluded you didn¡¯t need it. Why would I want one? Any other suggestions for a naive beginner? I am thinking about matching Z from antenna to receiver, but I can¡¯t measure either, and when I guess at values and then design a little LC circuit to match impedances, I find it will resonate at darn near my target f, sending my desired signal to ground!
Andy
On Feb 10, 2022, at 5:43 AM, Arie Kleingeld PA3A<pa3a@...> wrote:
Coming back on the title, how to measure...
I wrote an article about that a couple of months ago, measuring the input impedance of a Elecraft K3 receiver.
It was published in the SARC Communicator sept- Oct 2021. This is the link:
See page 43
73,
Arie PA3A
|
Roger Need
Donald S Brant Jr
Arie Kleingeld PA3A