Hi all,
I have been following the Q meter discussions here with great interest as I am a Q meter junkie.
One of my treasures is a Marconi TF1245 "Circuit magnification" (Q) meter. This consists of a base unit which is the actual Q meter and different exciters to cover the frequency range from audio to 300 MHz. The exciters are separate units that need to be bonded to the Q meter proper to avoid unwanted resonance effects as the connecting coax and instrument cases form a parasitic tuned circuit.
Until now I only had the VHF exciter but as I recently found a set of HF inductors for it I need to use it with the HF exciter (50 KHz to 50 MHz) as well. Now I only have a TF1246 HF exciter on loan and will have to return it soon so unless I can find a reasonably priced one I'll have to make something suitable.
The Injection resistor in the TF1245 is 0.02R and the injection voltage is 20 mV. The exciter is connected to it through a 0.48R resistor forming a 25:1 voltage divider so the exciter needs to provide 500 mV across 0.50R which is 500 mW or +27 dBm.? I plan to make up an adaptor to provide this from a signal generator. My HP8656B can provide +13 dBm into 50 ohms so I will need a gain of more than 13 dB and a 100:1 impedance transformation.
?I am thinking of beginning with an untuned amplifier at 50 ohms to get the level up to, say, 30 dBm (1 watt) and then a toroidal transformer with a turns ratio of 10:1 to match it to 0.5R. It's been a few years since i had to design such an amplifier so I'd like to find a module to do it. Any advice as to how to achieve this would be most welcome.
Thanks,
Morris
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Re: Tests on HP 4342A Q Meter and more
Mikek said "do you have an example?"
It's not something you would find and buy - rather a component layout arrangement. If you look at microwave/RF coaxial terminations and attenuating devices, you can see that they often use discus type resistors or even cylindrical complete sub-assemblies, where there are uniform sheets of resistive material, with current flowing from a center conductor to an outer one.in radial fashion. You can approximate this structure with discrete components. A bunch of parts in a radial arrangement is an easy way to get pretty close to the ideal continuous structure. A large or infinite number of them would do nicely, except that they would have to be shaped like slices of pie, while your common SMD parts are rectangles. So, you put a bunch of them in a radial pattern, like cylinders on a radial internal combustion aircraft engine. You can only fit so many in a given layout structure.
Ed
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For those interested in the details of various regulatory limits on conducted
and radiated EMI, the company TI has a nice overview summary:
While the two documents at this page cover respectively
conducted and radiated EMI specifically for power supplies,
the regulatory limits are of broader interest.? There has been
a lot of recent discussion on these issues over on the RFI reflector at
lists.contesting.com
Mike, K8CN
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I think those choppy bits that look like integral signs represent the measured current (Icm and Idm) since they seem to be multiplied by 25 or 50, which would appear to be impedance (Zcm and Zdm).
Donald.
On 1/26/23 15:19, Dr. David Kirkby, Kirkby Microwave Ltd wrote:
I detailed my experience with a piece of test equipment to measure the RF on our residential AC mains.
Thank you.?
The assumption is "AC mains exhibit an impedance of 50 ohms." This is a false assumption, and, if there is interest, I'll post some graphs from a study of AC mains impedance in the files
section.
It would be very specific to individual circumstances though.?
I chose to go with the design shown at:
I used two BN 73-202 binocular cores with a 6:6 turns.
There’s some writing on the left hand side. I originally thought it was 215 cm + 501 dm. Then it looks a bit like an integral. ??
This has been very educational project and it appears the FCC/EU/British Telecom doesn't even pay lip service to conducted EMI limits.
Thank you for sharing this.
Dave?
--
Dr. David Kirkby,
Kirkby Microwave Ltd,
drkirkby@...
Telephone 01621-680100./ +44 1621 680100
Registered in England & Wales, company number 08914892.
Registered office:
Stokes Hall Lodge, Burnham Rd, Althorne, Chelmsford, Essex, CM3 6DT, United Kingdom
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I think those choppy bits that look like
integral signs represent the measured current (Icm and Idm)
since they seem to be multiplied by 25 or 50, which would appear
to be impedance (Zcm and Zdm).
Donald.
On 1/26/23 15:19, Dr. David Kirkby,
Kirkby Microwave Ltd wrote:
toggle quoted message
Show quoted text
I detailed
my experience with a piece of test equipment to measure
the RF on our residential AC mains.
Thank you.?
The
assumption is "AC mains exhibit an impedance of 50
ohms." This is a false assumption, and, if there is
interest, I'll post some graphs from a study of AC mains
impedance in the files section.
It would be very specific to individual
circumstances though.?
I chose to
go with the design shown at:
I used two
BN 73-202 binocular cores with a 6:6 turns.
There’s some writing on the left hand side. I
originally thought it was 215 cm + 501 dm. Then it looks a
bit like an integral. ??
This has
been very educational project and it appears the
FCC/EU/British Telecom doesn't even pay lip service to
conducted EMI limits.
Thank you for sharing this.
Dave?
--
Dr. David Kirkby,
Kirkby Microwave Ltd,
drkirkby@...
Telephone 01621-680100./ +44 1621 680100
Registered in England & Wales, company number 08914892.
Registered office:
Stokes Hall Lodge, Burnham Rd, Althorne, Chelmsford, Essex, CM3
6DT, United Kingdom
|
I detailed my experience with a piece of test equipment to measure the RF on our residential AC mains.
Thank you.?
The assumption is "AC mains exhibit an impedance of 50 ohms." This is a false assumption, and, if there is interest, I'll post some graphs from a study of AC mains impedance in the files section.
It would be very specific to individual circumstances though.?
I chose to go with the design shown at:
I used two BN 73-202 binocular cores with a 6:6 turns.
There’s some writing on the left hand side. I originally thought it was 215 cm + 501 dm. Then it looks a bit like an integral. ??
This has been very educational project and it appears the FCC/EU/British Telecom doesn't even pay lip service to conducted EMI limits.
Thank you for sharing this.
Dave?
-- Dr. David Kirkby, Kirkby Microwave Ltd, drkirkby@...Telephone 01621-680100./ +44 1621 680100 Registered in England & Wales, company number 08914892. Registered office: Stokes Hall Lodge, Burnham Rd, Althorne, Chelmsford, Essex, CM3 6DT, United Kingdom
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Re: Tests on HP 4342A Q Meter and more
On Wed, Jan 25, 2023 at 06:01 PM, Ed Breya wrote:
I don't know if you're aware of a radial form of this kind of thing that's been around for a long time, used especially for coaxial terminations.
No, I am not aware, do you have an example. ????????????????????????????????????????? Mikek
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Re: Tests on HP 4342A Q Meter and more
Mikek,
I don't know if you're aware of a radial form of this kind of thing that's been around for a long time, used especially for coaxial terminations. It's just two concentric circles of Cu, with a bunch of paralleled SMD (or leaded) resistors arranged radially from the inner ring to the outer. It's assembled with conventional methods, with everything on-plane. The interconnects, feature sizes, ground planes etc depend on the purpose and environment.
Ed
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Re: Tests on HP 4342A Q Meter and more
I would like to see work towards a transformer or even a very low impedance drive resistance that is compatible with Banana connectors mounted 1" apart, hoping to keep it compatible. In the end a PCB supply house could take a design and send boards instead of everyone having a different design. ?However that does take some agreement on what the actual project is, because I doubt that 1" spacing is going to work for small value inductors at high frequency. (100MHz) ? Jacques has a simple approach in just knowing the errors and correcting for them. ?I would just like a more accurate instrument even if it is limited to 100kHz to 30MHz. The HP4342A was designed over 50 years ago, electronic components have changed size and many high impedance, high accuracy ICs have been developed, even, processors are cheap. I think with 50 years of progress, the HP 4342A can be improved on, with most of the components mounted on one PCB. ? Here is part of a board for using banana connectors and a low resistance driver that I started to draw up when someone mentioned using 7 SMD resistors to make a low inductance load. As they pointed out 7 is not magic. The info is in the old thread "Making a Q Meter" I don't remember the resistor values, but they were tiny to get us under 0.02Ω. Same applies with mounting a transformer, center leg is the banana Connector. Just my 2 cents :-) ??????????????????????????????????????? Mikek 
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Re: Tests on HP 4342A Q Meter and more
Way to go, Gerhard. I'm looking at a foil secondary too, and have been working on various schemes to build an appropriate mechanical structure for it. I don't know if you did the foil wrap only for test purposes, but I recommend using it for the actual secondary too. The trick is in working out a good structure that maintains low Z to the DUT connection.
Regardless of the core size, the center post should be as fat as possible, with a very close fit to the finished ID of the winding assembly. Then, a sheet of Cu foil can be wrapped tightly around the outside. One end of the wrapping becomes the approximate midpoint of the winding, bonded electrically to the center post. The other end of the wrapping can be cut open to clear the post, and sculpted into shape to form the ground connection (which is essentially a ring with the center post passing through it). And of course, you have to sculpt in a passageway for the primary leads. During all the forming and mounting steps, the foil can be finger-pressed to conform as tightly as possible to the toroid assembly. Also, depending on the methods and parts, some insulating materials like thin Kevlar or PTFE sheet may be needed in certain spots, especially soldering zones.
The version I'm presently working on is using an unknown junk box core similar to T130-1 or -2, as far as I can tell. My estimate of A sub L is about 14 nH, which is between the -1 and -2. The main reason for this core is that I happen to have some nice silver plated brass resonator posts out of a big old junked cavity filter. They're about 11/16" OD, which looks just about right to fit the core after it's loaded with the 0.030" D (whatever AWG that is) wire I have on hand. I just have to pick the right length to cut from the base. The resonators are tapped in the center for 8-32, but I'll redo it for 10-32, the shank size of the binding posts I'm using. So, the test voltage post will thread into the transformer's center, forming the low-Z source output, and the bottom end of the secondary foil will solder to a ground plane section. The back side midpoint foil of course has to be bonded well to the post by soldering or compression, and a big washer and 10-32 screw or stud, and include features to mount on an insulator, and a sound mechanical structure. The entire outer foil is "hot" with the test voltage, with about half on the back end where it mounts, so it has to be insulated to prevent undesired ground currents. It can be further contained by an added outer shield structure if needed. Since the voltage is small, it shouldn't be too much trouble, but you never know.
I've been picturing a small version too, with say a 1/4" D post made from a threaded brass spacer or shaft stock. The structure would be the same, except that the ground end of the foil would be soldered to a brass 1/4" ID x 3/8" threaded shaft bushing during construction. The bushing would be drilled out a little over-sized to provide clearance for a Kevlar insulation wrap, and the ground plane mount would be the bushing, so it attaches like a pot to a panel.
Ed
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Re: Tests on HP 4342A Q Meter and more
Hello Jacques, MikeK,
I have been following this thread with great interest and I have been thinking about constructing my own Q-meter.
I am also interested in lower frequencies and therefore choose a tape wound core to obtain wide bandwidth.
The first test was with 97 turns 0.50mm on VAC Vitroperm 500 T60006-L2025-W523, AL 28.4uH, 25 x 20 x 10mm.
This resulted in a low frequency limit of 84Hz in a 50 Ohm system.
To determine the achievable leakage inductance I wrapped the primary winding with a secondary wound with thin copper foil. This secondary was shorted and the secondary leakage inductance and resistance of a one turn secondary (as close to the primary as the foil) was determined by measuring the primary inductance and resistance and dividing by the primary turn squared: 0.3nH and 1.15 mOhm at 10MHz. At the HF end the first resonance is at 40MHz. This is probably due to the high number of turns. Apart from resonances of parasitic inductances and capacitances I don't think we will get beyond the frequency for which a quarter wavelength equals the length of the primary winding: one of the few things I remember from transmission line theory is the a quarter wave length of transmission line inverts the impedance: a short on one end is measured as an open on the other end. So reducing the transformer size and cascading transformers should help to increase the usable HF bandwidth
I also wanted to construct an oscillator from the resonant circuit under test by using the circuit current for feedback with the proper phase. The circuit current could be measured the a transformer similar to the drive transformer. The obvious disadvantage is a doubling of the series resistance and leakage inductance. But this can be circumvented if the level feedback is tapped after both transformers.
I should do some simulations!
Best regards,
Gerhard
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Re: Stepper Motor info needed for an Antenna Tuner project.
I only have information on one Philips stepper motor, but it might help someone else:
North American Philips Controls Corp 12 Volts 8 Watts 0-300 PPS K82701-P2 36 Ohms/coil 7.5 Degree per step 8 wire Stepper motor. I still have seven of these, somewhere.
Hi Chris , many thanks for replying.
Ive just had a phone chat with a colleague and he's emailed me the following link full of Philips databooks.
Thankfully ive found the info i need now.
I think i will download that achive in case in dissapears. Can never have enough databooks on file.
regards Pete
Hi Pete, Can you include a photo showing how many wires?
Coil resistance would help too.
Chris?
Hi everyone, im in the process of designing and building an automatic antenna tuner using some large variable caps. These are attached to Stepper motors for which i have no info.
The motors are Philips 400mN/M 1.8 deg.
Marked with the following numbers which i assume are part numbers :-
9904? 115? 23101
MB21? 4386
Ive tried searching for data on these motors without success, and i understand Philips no longer make stepper motors.
Has anyone got any datasheets or an old data book with the info please
Kind regards? Pete
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Re: Stepper Motor info needed for an Antenna Tuner project.
Hi Chris , many thanks for replying.
Ive just had a phone chat with a colleague and he's emailed me the following link full of Philips databooks.
Thankfully ive found the info i need now.
I think i will download that achive in case in dissapears. Can never have enough databooks on file.
regards Pete
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Hi Pete, Can you include a photo showing how many wires?
Coil resistance would help too.
Chris?
Hi everyone, im in the process of designing and building an automatic antenna tuner using some large variable caps. These are attached to Stepper motors for which i have no info.
The motors are Philips 400mN/M 1.8 deg.
Marked with the following numbers which i assume are part numbers :-
9904? 115? 23101
MB21? 4386
Ive tried searching for data on these motors without success, and i understand Philips no longer make stepper motors.
Has anyone got any datasheets or an old data book with the info please
Kind regards? Pete
|
Re: Stepper Motor info needed for an Antenna Tuner project.
I think this is the part number 9904? 115? 23101 I think this is the batch code and build date MB21? 4386 Hope it helps. Nigel ?
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From: [email protected] <[email protected]> On Behalf Of Pete Harrison
Sent: 25 January 2023 12:27
To: [email protected]
Subject: [Test Equipment Design & Construction] Stepper Motor info needed for an Antenna Tuner project.? Hi everyone, im in the process of designing and building an automatic antenna tuner using some large variable caps. These are attached to Stepper motors for which i have no info. The motors are Philips 400mN/M 1.8 deg. Marked with the following numbers which i assume are part numbers :- 9904? 115? 23101 MB21? 4386 Ive tried searching for data on these motors without success, and i understand Philips no longer make stepper motors. Has anyone got any datasheets or an old data book with the info please Kind regards? Pete
|
Re: Stepper Motor info needed for an Antenna Tuner project.
Hi Pete, Can you include a photo showing how many wires? Coil resistance would help too. Chris?
Hi everyone, im in the process of designing and building an automatic antenna tuner using some large variable caps. These are attached to Stepper motors for which i have no info.
The motors are Philips 400mN/M 1.8 deg.
Marked with the following numbers which i assume are part numbers :-
9904? 115? 23101
MB21? 4386
Ive tried searching for data on these motors without success, and i understand Philips no longer make stepper motors.
Has anyone got any datasheets or an old data book with the info please
Kind regards? Pete
|
Stepper Motor info needed for an Antenna Tuner project.
Hi everyone, im in the process of designing and building an automatic antenna tuner using some large variable caps. These are attached to Stepper motors for which i have no info.
The motors are Philips 400mN/M 1.8 deg.
Marked with the following numbers which i assume are part numbers :-
9904? 115? 23101
MB21? 4386
Ive tried searching for data on these motors without success, and i understand Philips no longer make stepper motors.
Has anyone got any datasheets or an old data book with the info please
Kind regards? Pete
|
Re: Tests on HP 4342A Q Meter and more
?Since we are fighting inductance, Does a lower impedance transformer help reduce output inductance? If not, my point is not helpful. Alan G8LCO, suggested a 10Ω to 1 turn transformer with a 10Ω drive impedance, in the original "making a Q meter" thread ? Alan? said the following, "Don't think much of the 50:1 transformer at all, HP used it as a cheap way of producing a low source impedance up to mid HF. Using a 2-mix core is not great either, I went for a 3C90 core for an adapter that I mentioned on another group, 10 turn primary and 1 turn secondary transformed a 4:1 pad of 39 and 10 ohms down to 0.08 ohms source that was flat from 3KHto >>150MHz. Inserting a second cascaded similar transformer would produce a 100:1 stepdown in voltage but a 1/10,000 reduction in impedance without great transformer issues or drive amp complexity.
Generally it is fair to say that non-transmission line transformers become "difficult" when the ratio goes beyond 10 or that many more than 20 turns are involved, stray reactance then tends to become problematic? at very wide bandwidths. However if you stick to modest ratio's and few turns on the smallest core available ( have a look at minicircuit's wideband transformers) then you can have an easier time than others. This leads to using ferrites rather than dust iron cores ( not 2-mix for example)."
This it what I think he did, then he suggest another 10 to 1 transformer to go even lower output impedance.
?????????????????????????????????????? Mikek
?
?
?
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Re: Tests on HP 4342A Q Meter and more
Sorry, it should be 5 nanoHenry ! Thanks for pointing this out. Jacques
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Re: Tests on HP 4342A Q Meter and more
On Tue, Jan 24, 2023 at 05:19 AM, Alan wrote:
Ls=5uH ????? 5uH is? the inductance of a? thin wire in a circle of 1m diameter, 5nH might be more appropriate.
I'm pretty sure that's a typo, in his previous post with the PowerPoint attachment, he has .05nH and 3nH examples. Good catch though! ???????????????????????????? Thanks, Mikek ???????????????????????????????????????????????
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Re: Tests on HP 4342A Q Meter and more
Ls=5uH ????? 5uH is? the inductance of a? thin wire in a circle
of 1m diameter, 5nH might be more appropriate.
73.
Alan G8LCO
On 23/01/2023 21:06, Jacques Audet
wrote:
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Hi
Mikek,
You wrote:
< the negative effect of reactance of the drive
transformer. I haven't understood, how the reactance affects the
measurement >
When you resonate the Q meter the coil inductance L, and
the source Ls add up so that:
- The resonant frequency will decrease. (compared to not
having Ls)
- This increases the total reactance XL, since we have two
inductors in series.
- The? Q = XL/Rs? so the Q will increase slightly by a
small amount.? More increase above 10 MHz and with high resonant
C.
The effect of Rs is generally larger and overall the
measured Q factor decreases .
My Excel sheet has been revised to add the corrections for
both Rs and Ls, the source resistance and reactance,
for the HP4342A and the Boonton 260? Q Meters.? (For the
Boonton I assumed Rs=0.02 ohms and Ls = 5 uH, but it can be
changed)
Hope this helps,
Jacques
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Re: Tests on HP 4342A Q Meter and more
Hi Mikek,
You wrote:
< the negative effect of reactance of the drive transformer. I haven't understood, how the reactance affects the measurement >
When you resonate the Q meter the coil inductance L, and the source Ls add up so that:
- The resonant frequency will decrease. (compared to not having Ls)
- This increases the total reactance XL, since we have two inductors in series.
- The? Q = XL/Rs? so the Q will increase slightly by a small amount.? More increase above 10 MHz and with high resonant C.
The effect of Rs is generally larger and overall the measured Q factor decreases .
My Excel sheet has been revised to add the corrections for both Rs and Ls, the source resistance and reactance,
for the HP4342A and the Boonton 260? Q Meters.? (For the Boonton I assumed Rs=0.02 ohms and Ls = 5 uH, but it can be changed)
Hope this helps,
Jacques
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Dr. David Kirkby, Kirkby Microwave Ltd
Michael A. Terrell
Chris Hayes
