For accurate measurements the "damping" material needs to be 1/2 wavelength thick, ie 6 inches at 1kHz.
The sound source should have a reasonable frequency response and reasonably low distortion.
Reasonable is context sensitive !
If you have high distortion in the sound source (likely with a moving iron transducer) then a harmonic of the the frequency you mean to measure at may con-incide with a peak in the response of the system or the microphone under test, leading to large errors in measurements.
The setup in your picture will be very sensitive to small changes in geometry at higher frequencies.
You can asses the repeatability of your measurements easily by performing several tests (10 would be a good starting point) and completely disconnecting and disassembling your rig between tests. In my former life making accelerometers to sell into the automotive business we called this a "Gauge Repeatability Test". Results could be very disapointing, especially with mechanical measurments. We would have done 10 tests each on at least three different test samples.
The accuracy of your measurements can't be determined without some kind of reference devices.
MK
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Re: Boonton 260A Q Meter / Pete Orin 260A Boonton Guru communication
Use Reply To Sender, rather than broadcasting.
?
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From: [email protected]
[mailto:[email protected]] On Behalf Of Mikek
Sent: Tuesday, 1 November 2022 1:34 PM
To: [email protected]
Subject: Re: [Test Equipment Design & Construction] Boonton 260A Q
Meter / Pete Orin 260A Boonton Guru communication
?
I'm pretty sure we both thought we were having a private
exchange! :-)
??????????????????????????????????????
Mikek
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Re: Boonton 260A Q Meter / Pete Orin 260A Boonton Guru communication
I'm pretty sure we both thought we were having a private exchange! :-)
?????????????????????????????????????? Mikek
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Re: Boonton 260A Q Meter / Pete Orin 260A Boonton Guru communication
Ok, I appreciate it.
?We live on the end of a street at major road, we don't get many
people down this far, we
haven't passed out candy for 15 years. Also, not many kids in
our 98 home subdivision anymore.
?I had a miniwhip antenna up for a while, Hurricane Michael
knocked it down. It did pretty good as a wideband antenna.
I had to knock down a noise source though. I had a bad noise
making it completely unusable up and down the band. I finally
traced
it to an outdoor light with an infrared sensor. I put a Corcom
line filter on it and cleaned it up.
? We had a lot of damage from the hurricane, so when it came to
to install 5 new outdoor lights,
I bought a couple brands and tested them for noise, one I bought
was very rf noise free, so went back and bought 4 more.
A short video comparing 100ft sloping long wire, to the miniwhip
to, my 300ft beverage on the ground.
???????????????????????????????? Mikek
On 10/31/2022 7:36 PM, John Kolb wrote:
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Hi Mike,
Tracking number: 9500 1152 6253 2304 7149 03.? Should be there
Friday. Postage was $ 5.40.? I also included a pair of 2N3866 NPN
transistors. The 2N3819's and 2N3866's are leftovers from when I
was selling active antennas.
Lots of traffic today with all the kids out trick or treating Main
St.
John
On 10/31/2022 6:19 AM, Mikek wrote:
Re the FET voltmeter mod: I'm only finding
the 2N5245 available from China, 10 for $10.96 plus $2.50
shipping.
If anyone orders them, I'll slip $4 in an envelope for one, or
if someone finds a replacement on DigiKey,
??I would order from there.
--?
Thanks, Mikek
--
Thanks, Mikek
|
Re: Boonton 260A Q Meter / Pete Orin 260A Boonton Guru communication
Hi Mike,
Tracking number: 9500 1152 6253 2304 7149 03. Should be there Friday. Postage was $ 5.40. I also included a pair of2N3866 NPN transistors. The 2N3819's and 2N3866's are leftovers from when I was selling active antennas.
Lots of traffic today with all the kids out trick or treating Main St.
John
toggle quoted message
Show quoted text
On 10/31/2022 6:19 AM, Mikek wrote: Re the FET voltmeter mod: I'm only finding the 2N5245 available from China, 10 for $10.96 plus $2.50 shipping.
If anyone orders them, I'll slip $4 in an envelope for one, or if someone finds a replacement on DigiKey,
?I would order from there.
--
Thanks, Mikek
|
Re: Boonton 260A Q Meter / Pete Orin 260A Boonton Guru communication
While looking for something else, I found a nice copy of the FET mod in the files section under Boonton / HP
of the HP/Agilent/Keysight IO group.
/g/HP-Agilent-Keysight-equipment/files/HP%20%20Boonton/HP%20%20Boonton%20%20535%20for%20BRC%20260%20%20Q%20meter/Boonton_535_fet_repl.pdf
--
Thanks, Mikek
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Today's update: The setup similar to what's shown in the picture seems to work well for my purposes. - The "speaker" is an old Shure "Controlled-Magnetic Transducer", as found in old hand mics from mobile police radios and such. It's a lot better than the 4" radio speaker. [Trivia: I looked up the Shure patent filed in 1941, and it is a "magnetic translating device", not specifically a microphone, so the patent intends for it to work in either direction.] - The distance is just a couple inches, and is not very critical. - The "damping" is currently an old rag, to reduce reflections from the bench surface. I don't think I'll bother to build a complete enclosure, since I'm not trying to do precise measurements. I'll just build a simple wood fixture to hold the pieces, with a way to adjust the adjust the position of the 2 mics. Jeff Green: I hope your ulcer issue gets resolved positively in the near future! In a couple of weeks, I'm having hernia-repair surgery (it's not real troublesome, mostly just annoying). Pete 
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Re: Boonton 260A Q Meter / Pete Orin 260A Boonton Guru communication
On Mon, Oct 31, 2022 at 10:23 AM, v321uk wrote:
I too would love to see Pete's solution.
I posted it in post #1111. ? -- Thanks, Mikek
|
Usually they are made of polypropylene as well as many pharmacy supplied pill bottles (the orangish brown ones).
Sam
Sam Reaves
ARS W3OHM
Owner / Moderator of: LeCroy Owners Group on Groups.io
Sencore Owners Group on Groups.io Sprint Layout Group on Groups.io?? Pulsonix EDA Group on Groups.io
LPKF Owners Group on Groups.io
Electronics and Mechanical Hardware Design Engineering Manager
Staff Scientist Andritz Rolls Global Research Center (RETIRED)
Mikek
Thanks I have saved a copy of this to study.? I would like to find out what the plastic in my Insulin Syringes is, I have checked the Mfg. Website, no mention.? They would make good VHF or UHF? coilforms.
Leon Robinson ?? K5JLR
Political Correctness is a Political Disease.
Politicians and Diapers should be changed
often and for the same reasons.
On Sunday, October 30, 2022, 12:56:18 PM CDT, Mikek < amdx@...> wrote:
On Sun, Oct 30, 2022 at 10:35 AM, Leon Robinson wrote:
I have heard this many times over the years but have never seen? any documentation.? I can see that in a final tank coil it wouldn't be suitable for thermal reasons.
Checkout this page and compare PVC at 60 vs crystal polystyrene at 1. Or PTFE (Teflon) at 2. ?But again no frequencies of the tests, but the page does mention it matters. ? -- Thanks, Mikek
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Re: Boonton 260A Q Meter / Pete Orin 260A Boonton Guru communication
Mike
I too would love to see Pete's solution.
John G3UGY
|
Re: Boonton 260A Q Meter / Pete Orin 260A Boonton Guru communication
On Mon, Oct 31, 2022 at 09:37 AM, Mikek wrote:
You probably should stick to the? MMBF-J20 because of its higher voltage.
I just noticed this on the MMBF-J20 datasheet, " This device is designed primarily for low level audio"
Makes me wonder how it would work at 70MHz on the 260A, not that I ever get that high, but...? -- Thanks, Mikek
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Re: Boonton 260A Q Meter / Pete Orin 260A Boonton Guru communication
On Mon, Oct 31, 2022 at 09:18 AM, Chuck Moore wrote:
The MMBF-J201? and the MMBF-J310
look to be potential subs.
You probably should stick to the? MMBF-J20 because of its higher voltage. ?A quick voltage divider of the 258V, 170kΩ and 22kΩ? sets the drain at 29.6V with no current through the FET. The MMBF-J20 is 40V, the MMBF-J310 is only 30V. ?I have some 2SK192A FETs in an order box from China, because I don't know of a good substitute. ?Here is the only info I can find on the 2SK192A, I want to try building the high impedance amp I posted earlier and see if it will get past 30Mhz flat, I'd like to go with the transistors in the original design, or something that would do the same job. ?I could go surface mount if the proper chips were available. ?Any ideas?  ? -- Thanks, Mikek
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Re: Boonton 260A Q Meter / Pete Orin 260A Boonton Guru communication
Here is a message Pete posted on the use of the 2N5245 and his recommendation for pretty much any JFET as a sub.
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Re: Boonton 260A Q Meter / Pete Orin 260A Boonton Guru communication
Morning Mike
After a few bad experiences buying micros on e-Bay, I use it as
a last resort for silicon these days.
Like you I found that the 2N5245 was obsolete. So I went looking
for potential replacements.? The MMBF-J201? and the MMBF-J310
look to be potential subs. The 201 is rated for 350 mW dissipation
which matches the 2N5245. The 310 is rated for 250 mW. Pete did
say he pulled the 2N5245 because it was what was in his parts bin,
there was nothing special about it. So my guess is either the 201
or 310 will work.
The MMBF-J201 and MMBF-J310 are the current variant of the
Siliconix U210 and U310 from decades past. They were popular
as they allowed a common gate configuration that offered decent
power gain at VHF/UHF without wanting to oscillate.
Chuck
On Oct 31, 2022, at 9:19 AM, Mikek <amdx@...> wrote:
Re the FET voltmeter mod: I'm only finding the 2N5245 available from China, 10 for $10.96 plus $2.50 shipping.
If anyone orders them, I'll slip $4 in an envelope for one, or if someone finds a replacement on DigiKey,
?I would order from there.
--
Thanks, Mikek
|
Exactly. A useful approximation is that sound travels about 6 orders of magnitude more slowly than light. So, for a given frequency, audio wavelengths are a million times shorter. Or, for a given wavelength, audio frequencies are a million times lower. And the product of frequency and wavelength is 300 GHz-mm for EM waves.
Tom Sent from my iThing; please forgive the typos and brevity
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On Oct 31, 2022, at 05:18, Brian <brianclarke01@...> wrote:
?
Hello Anonymous,
Sound travels at about 300 m/s. So, the wavelength of a 1 kHz
audio signal would be closer to 300 mm.
You might want to trade in your calculator for calculating the
wavelength of a 9.5 GHz RF signal, too.
EM waves travel at about 300 Mm/s. So, the wavelength of a 9.5 GHz
signal would be 31.6 mm.
See if you can get your EE professor to explain how to express
weights and measures.
73 de Brian, VK2GCE_,_
|
Re: Boonton 260A Q Meter / Pete Orin 260A Boonton Guru communication
Re the FET voltmeter mod: I'm only finding the 2N5245 available from China, 10 for $10.96 plus $2.50 shipping.
If anyone orders them, I'll slip $4 in an envelope for one, or if someone finds a replacement on DigiKey,
?I would order from there.
--
Thanks, Mikek
|
Re: Boonton 260A Q Meter / Pete Orin 260A Boonton Guru communication
Here's a slightly better picture.
Still have not got my scanner working, (may be time for new one).
--
Thanks, Mikek
|
Hello Anonymous,
Sound travels at about 300 m/s. So, the wavelength of a 1 kHz
audio signal would be closer to 300 mm.
You might want to trade in your calculator for calculating the
wavelength of a 9.5 GHz RF signal, too.
EM waves travel at about 300 Mm/s. So, the wavelength of a 9.5 GHz
signal would be 31.6 mm.
See if you can get your EE professor to explain how to express
weights and measures.
73 de Brian, VK2GCE
?
toggle quoted message
Show quoted text
From: [email protected]
[mailto:[email protected]] On Behalf Of Jeff
Green
Sent: Monday, 31 October 2022 10:28 PM
To: [email protected]
Subject: Re: [Test Equipment Design & Construction] microphone
testing
?
This might be
relevant:?
?
I’d taking some EE
classes and a professor explained how British engineers used audio to verify
microwave antenna for radar. It was easier and safer to work with audio then
RF.
1kHz would have a
wavelength of 30mm, which would be 9.5GHz…if I’ve done the math right. I
suspect it was a lot easier to produce 1kHz of audio then 9.5GHz of RF.
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Re: Boonton 260A Q Meter / Pete Orin 260A Boonton Guru communication
Thank you Mike.? This is more than sufficient for me.
Regards
Chuck
|
Re: Boonton 260A Q Meter / Pete Orin 260A Boonton Guru communication
Here's a quick picture for tonight, I'll try to do better tomorrow.
--
Thanks, Mikek
|
Brian
John Kolb
saipan59 (Pete)
Sam Reaves
