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Vintage Test Gear and Workshop Equipment For discussions about vintage test gear and workshop equipment such as coil winders.

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Old 20th Jan 2023, 12:41 pm   #1
mickm3for
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Default Q meter

Hi any ideas on building a Q meter or any for sale Mick
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Old 20th Jan 2023, 6:19 pm   #2
WME_bill
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Default Re: Q meter

Mike, I have a complete Marconi Q Meter set with signal source oscillators. Model TF1245 Q Meter and TF1246 Oscillator 40khz to 50Mhz and Oscillator TF1247 20Mhz to 300Mhz. With all manuals and accessories. All working a year ago. I would prefer to pass on as a complete set. If of any interest, I will work out a price to comply with Forum rules.
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Old 20th Jan 2023, 6:44 pm   #3
G6Tanuki
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Default Re: Q meter

There was a design for a Q-meter in an edition of PW some time in the late-70s/mid-80s.

The basic aspect was a tunable oscillator/amplifier stage operating at HF that was loosely coupled to the coil/capacitor under test which were set up as a parallel-resonant circuit, with a RF voltmeter that measured the peak voltage across the circuit.

There was then a low-value [a couple of Ohms] non-inductive resistor that could be switched in series with the coil, and from seeing how this affected the RF voltage across the now-additionally-lossy tuned-circuit, the Q could be extrapolated.


Maybe an exploration of the PW archive on the worldradiohistory site would reveal it?
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Old 20th Jan 2023, 7:48 pm   #4
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Default Re: Q meter

Quote:
Originally Posted by G6Tanuki View Post
There was a design for a Q-meter in an edition of PW some time in the late-70s/mid-80s.
The circuit is in Nov.'78 edition, but..... It utilises a FET as a buffer amp, in a style of circuit seen in many publications, but in recent years, knowledgeable people on this Forum using LT Spice have said will exhibit high negative resistance and won't/shouldn't work.

B
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Old 20th Jan 2023, 7:55 pm   #5
Philips210
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Default Re: Q meter

G6Tanuki, that was the PW 'Sarum' from November 1978.

There was also some good discussion here: https://www.vintage-radio.net/forum/...d.php?t=154320

The Q meter ex member Argos25 recommended looks a good project.

Regards,
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Old 20th Jan 2023, 8:25 pm   #6
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Default Re: Q meter

Hi all,
Q-meter is a very nice euipment, was intended by Boonton in (I think 1938) and all other Q-meters are practically a copy af their product the 160, some as 100% identic peace -visually too...
HP aquired in 1959 firm Boonton and his knowledge too.
I worked much with Bills Marconi system, that was very nice set, but BULKY, 30 years later I become possibility to by cheap a HP 4342A -was produced between 1970-93, its a fine, transportable and precize/stabile bag cased equipment.
It works between 22KHz and 70MHz, measures Q in a range of 5 to 1000; usually it is quite expensive on the market so at 1000$ on auctions sites.
If I would build a Q-meter, I would wish to make so an example, BUT it isn`t a simple job: needs i.e. a very good variable capacitor-practically up to 500 pF and so on...
K.
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Old 21st Jan 2023, 5:45 pm   #7
mickm3for
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Default Re: Q meter

Hi its just dawned on me why not use the nano vna to plot the + and -3dB pionts and calc Q from this Mick
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Old 21st Jan 2023, 6:30 pm   #8
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Default Re: Q meter

Quote:
Originally Posted by Bazz4CQJ View Post
Quote:
Originally Posted by G6Tanuki View Post
There was a design for a Q-meter in an edition of PW some time in the late-70s/mid-80s.
The circuit is in Nov.'78 edition, but..... It utilises a FET as a buffer amp, in a style of circuit seen in many publications, but in recent years, knowledgeable people on this Forum using LT Spice have said will exhibit high negative resistance and won't/shouldn't work.

B
That's the one I remember, yes.

I never built it but despite what the subsequent simulations may have suggested, I had good reports of its efficacy from people who did build them and used them to optimise HF power-amplifier tank-circuits and select the 'best' combinations of toroid-characteristics/number-of-turns in low-pass-filters.
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Old 29th Jan 2023, 3:56 pm   #9
David G4EBT
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Default Re: Q meter

The 'Sarum' 'Q' Meter was the November 1978 Practical Wireless front cover project.

The link to that addition of PW is here:

https://worldradiohistory.com/UK/Pra...PW-1978-11.pdf

However, two crucial pages of the article are missing, namely, pages 64 & 66.
(Page 66 has the coil winding details).

I still have the original article as at one point I'd considered building it, but never did. It's a common tale.
Many more 'gunners' firing blanks than there are constructors! (I'm 'gunner build this, I'm 'gunner build that').

I've scanned the two missing pages in case it might help someone.

I guess one hurdle would be to source the 'Aladdin' style 7mm coil formers with dust iron cores, which used to be so commonplace back then.

See Aladdin Coil Former thread:

https://www.vintage-radio.net/forum/...d.php?t=122173
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Old 29th Jan 2023, 4:05 pm   #10
Philips210
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Default Re: Q meter

Thank you for posting the missing pages to the article David.

I'm sure David Gleason at World Radio History would be pleased to have those missing pages to help complete the Nov 1978 issue.

Regards,
Symon.
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