|
Vintage Test Gear and Workshop Equipment For discussions about vintage test gear and workshop equipment such as coil winders. |
|
Thread Tools |
24th Feb 2019, 12:00 am | #1 |
Heptode
Join Date: Nov 2018
Location: London SW16, UK.
Posts: 655
|
Q-meter questions
I am looking for a Q-meter to be used for testing homebrew RF, IF and oscillator coils.
PM please for offer. I have been measuring Q with the ring-down method but it is not accurate with basic scope and function generator. At the moment I can only predict unload Q with software. Sing |
24th Feb 2019, 12:09 pm | #2 |
Rest in Peace
Join Date: Jun 2006
Location: Chard, South Somerset, UK.
Posts: 7,457
|
Re: Q-meter wanted
I don't have a Q-meter for sale. However, I would recommend you look for an Advance T2 Q-meter. I have one here and is a useful piece of test equipment. The lowest freq. that it will resonate a coil to is 100 kHz. If you do acquire one, you will need the manual: it's available on the www.
Marconi made a Q-meter. I've never used one, but I have read reports that it a bit tricky to use. (And, I might add, in my experience, as an item from Marconi, that is what I would expect). Al. |
24th Feb 2019, 1:04 pm | #3 |
Heptode
Join Date: Nov 2018
Location: London SW16, UK.
Posts: 655
|
Re: Q-meter wanted
Thanks for the advice. I don't see them around often.
|
24th Feb 2019, 1:15 pm | #4 |
No Longer a Member
Join Date: Oct 2016
Location: Maroochydore, Queensland, Australia.
Posts: 2,679
|
Re: Q-meter wanted
By far and away the best Q meter I have seen was a "build your own version" in Electronics Australia, June 1969.
The thing that makes me laugh about it, they called it the "Economy Q Meter" It is far far better than most Q meters and is a wonderful project to build, just as good now as when they published it. I've attached some scans, obviously not the whole article. But the whole design of it, the mathematical support, operating instructions, the construction article and details are just wonderful. If you want the whole article, all you have to do is email Silicon Chip (they have this archived) and they will send you the entire article. |
24th Feb 2019, 5:16 pm | #5 |
Heptode
Join Date: Nov 2018
Location: London SW16, UK.
Posts: 655
|
Re: Q-meter wanted
Thanks the article. Without a Q-meter, it is not the end of the world. I can always rely on design rule of thumb and approx. known values such as graphs from Terman:
https://www.robkalmeijer.nl/techniek...e33/index.html Last edited by regenfreak; 24th Feb 2019 at 5:22 pm. |
26th Feb 2019, 1:12 am | #6 |
Dekatron
Join Date: Sep 2010
Location: Cheltenham, Gloucestershire, UK.
Posts: 3,077
|
Re: Q-meter wanted
Back in the 1990s I used the classic Marconi TF1245 Q meter to aid in design for high performance LPF, HPF and BPF filters. This was generally for filters across all bands from <100kHz to a few hundred megahertz. But this meter is big and bulky especially when fitted with both oscillator options and it needed lots of maintenance to keep it working on all its ranges. So I can't recommend it in 2019. Probably the best Q meter in those days was the HP4342A but these are rare and expensive unless you get lucky.
If you don't manage to find/buy a Q meter then there are various (fairly simple) methods you can use to measure inductor Q across the HF bands and up into VHF. I've not used a Q meter in probably 15-20 years because I don't think they are needed for general RF design in 2019. Because of the abundance of accurate test generators and detectors these days it is possible to lash something up (to measure Q) in a basic test jig that will be more trustworthy than a 40-50 year old Q meter that will have seen a few repairs and bodges during its lifetime. So I'd argue these old Q meters are a waste of space unless you need to measure the Q of lots of inductors in a short time. The only exception is the HP 4342A Q meter. I wouldn't say no to one of those but they are rare and expensive!
__________________
Regards, Jeremy G0HZU |
26th Feb 2019, 12:41 pm | #7 |
Heptode
Join Date: Nov 2018
Location: London SW16, UK.
Posts: 655
|
Re: Q-meter wanted
Hi Jeremy
Thanks for the advice. I agree. It is one of those things that it is nice to have but there are many ways of working around it. Funny enough, the only reason that I had the "desire" to buy a Q-meter was that I was reading the manual for the HP4342 last week. Someone in another forum had suggested me to download the manual and look at the method used in HP4342 instructions of measuring the stray capacitance of an inductor . But the method had turned out to not useful. But I must say the HP4342 manual has one or two interesting graphs and I was intrigued by them. There are a few online unloaded Q calculators, like this modern one using "helical waveguide mode" method (it seems very advanced but is not very good for working stray capacitance): http://hamwaves.com/inductance/en/index.html#input |
26th Feb 2019, 1:17 pm | #8 |
Rest in Peace
Join Date: Jun 2006
Location: Chard, South Somerset, UK.
Posts: 7,457
|
Re: Q-meter wanted
Many years ago, a design for a home-build Q-meter appeared in an issue of Practical Wireless magazine. Several years later, I bought a second-hand one. Briefly stated, it was almost useless. So I suggest that if you do see one offered, walk away!
Al. |
26th Feb 2019, 3:18 pm | #9 | |
Dekatron
Join Date: Sep 2010
Location: Cheltenham, Gloucestershire, UK.
Posts: 3,077
|
Re: Q-meter wanted
Quote:
My experience of advanced inductor modelling dates back to the early 1990s at my place of work. We have to model inductors out to frequencies several times higher than the first resonance mode because we do a lot of ultra wide bandwidth design. Our goal was to produce real working (complex transmission line based) models rather than to try and produce equations to predict where resonances occur. However, these days we mainly use 2 port VNA models for SMD inductors as this is quick, convenient and is usually adequate for SMD inductors that have lowish Q. But our old transmission line based models from the 1990s were very powerful and much better than the classic/flawed inductor models based on lumped components.
__________________
Regards, Jeremy G0HZU |
|
26th Feb 2019, 3:24 pm | #10 |
Dekatron
Join Date: Sep 2010
Location: Cheltenham, Gloucestershire, UK.
Posts: 3,077
|
Re: Q-meter wanted
Coilcraft offer some info on how to model SMD inductors using a crude transmission line model here:
https://www.coilcraft.com/pdfs/spice_132.pdf This is better than a lumped model but still fairly hopeless as a wideband model (out to several GHz) as it won't model the higher resonance modes correctly. ... but none of this will help you buy that Q meter. Someone on here may have one for sale. If it's an HP4342A I'll out bid you for it (just kidding )
__________________
Regards, Jeremy G0HZU Last edited by G0HZU_JMR; 26th Feb 2019 at 3:44 pm. |
26th Feb 2019, 5:56 pm | #11 |
Heptode
Join Date: Nov 2018
Location: London SW16, UK.
Posts: 655
|
Re: Q-meter wanted
Thanks. I don't know much about Ham radio but every time I look for any information I ended up reading articles written by Ham guys. I am only interested in unloaded Q prediction up 10 MHz for MW tank/oscillator radio and tesla coils design. I would stay away from the "black magic" of transmission line theory up to GHz. The maths of the VHF stuff boggles my mind.
It appear that the HP4342 is "an object of desire" then. It also seems that the owners of the HP4342 (guys from another forum) do not normally understand the logic of the testing steps outlined in the manual. Last week I was trying to figure out why certain test have to be done in specific steps and the HP4342 manual does not really explain the rational behind those testing procedures. Other less known Q meters would require lots of skills to restore and maybe it would be difficult to use correctly without the user manuals. |
26th Feb 2019, 7:08 pm | #12 |
Dekatron
Join Date: Sep 2010
Location: Cheltenham, Gloucestershire, UK.
Posts: 3,077
|
Re: Q-meter wanted
Wow, I'm not so sure about testing Tesla coils for Qu. I keep away from scary stuff like Tesla coil/machines so I have no idea what spec of Q meter you would need. Most of the RF stuff I do these days is SMD but in the 1990s I did make a lot of coils for filters across LF through VHF and these were fairly large coils with lots of turns. I often used Litz wire for the LF stuff with various RM cores from Siemens to achieve a Qu up in the 400-500 range.
Most Q meters I've seen operate on the principle that Q can be approximated by E/e. Whilst this is an elegant way to do it, it does make it hard to realise the source and detector requirements if you want to test coils that have a low ESR or high Rp at the test frequency. That's when the decent Q meters leave the cheap and basic Q meters behind. It's also why I prefer to use other means to measure Q these days because I feel more confident in the results. But for simple and typical MW coils that have moderate Qu I think you would be OK with a fairly old and basic Q meter. I can't comment on your Tesla coil requirements though!
__________________
Regards, Jeremy G0HZU |
26th Feb 2019, 7:27 pm | #13 | |
Nonode
Join Date: May 2007
Location: Redruth, Cornwall, UK.
Posts: 2,573
|
Re: Q-meter wanted
Quote:
Regards Symon |
|
26th Feb 2019, 11:02 pm | #14 |
Dekatron
Join Date: Jan 2004
Location: Newcastle upon Tyne, Tyne & Wear, UK.
Posts: 8,194
|
Re: Q-meter wanted
Hi Guys, the best and simplist Q meter for the OP's application is the Advance T2.
It is simple to use and is fitted with calibrated variable C and goes from 50KHz to 100MHz. It will allow Q and delta q measurements, as well as dynamic R and self cap of the test coil. It has a small platform that allows accurate measurements. A rats nest of wires will not give accurate Q figures. Parts to replace are black hunts caps that are not in the measuring circuit and valves (2) are easy to obtain types. Used to be quite common on ebay but not seen one for a while. Use with a Tesla coil would only be at very low power as the coil would only be energised form the meter. Ed |
27th Feb 2019, 12:06 am | #15 | |
Heptode
Join Date: Nov 2018
Location: London SW16, UK.
Posts: 655
|
Re: Q-meter wanted
Quote:
Just out of historical interest in vintage technology, I made a few spiderweb RF coils with 100 threads Litz wire, I think the Qu of spiderweb coils can go over the maximum limit of some Q meters; probably Qu reaches over 400. In that case software prediction or measurement methods using scope and signal generator are the only way forward. T2A looks beefy and solid. The maximum Q for HP4342A is 300 (up to 1000 with certain supplemental inductor combo) The maximum Q for T2A is 400 Last edited by regenfreak; 27th Feb 2019 at 12:23 am. |
|
27th Feb 2019, 12:18 am | #16 | |
Moderator
Join Date: Mar 2012
Location: Fife, Scotland, UK.
Posts: 22,864
|
Re: Q-meter wanted
Quote:
There was also a Boonton Rx meter and of course, General radio's RF bridge. But give me a 4342A any day David
__________________
Can't afford the volcanic island yet, but the plans for my monorail and the goons' uniforms are done |
|
27th Feb 2019, 12:54 am | #17 |
Dekatron
Join Date: Sep 2010
Location: Cheltenham, Gloucestershire, UK.
Posts: 3,077
|
Re: Q-meter wanted
If there is interest in discussing this stuff in detail then maybe it would be better to do it on a dedicated thread in the Test Gear section. I would certainly contribute to it. I've measured Q in lots of ways over the years and I abandoned the old Q meters many years ago. We threw our Marconi TF1245 away some time around 2000-2005 as no one had used it in ages. The TF1246/7 oscillator coils tend to fail on certain ranges (they can be fixed) and we had trouble every year we sent the complete 1245/6/7 assembly for 'calibration'.
Typical issues were to do with the cal house wanting to engrave a new capacitance dial (at immense cost) every other year or so and they also bleated every year about the detector diode (valve) failing their tests. They wanted to import the diode valve from the US at a crazy cost and they wouldn't guarantee the new diode would be any better than the old one. So every year we asked for a restricted calibration rather than spend money on it. That's why I would urge caution with this meter. If you find one it's probably had several sets of fingers in it to fix the usual failures and it will be unlikely to be in spec any more. However, I have fond memories of using it because it can be very rewarding seeing that Q needle climb just a little bit higher than it did with a previous coil design! I was chasing coil Q of >400 down at frequencies below 1MHz in the early days and I spent a LOT of time playing with pot cores and various types of Litz wire. I don't think the meter was very accurate when used like this but I was looking for increases rather than trust the Q dial.
__________________
Regards, Jeremy G0HZU |
27th Feb 2019, 3:33 am | #18 | |
Dekatron
Join Date: Sep 2010
Location: Cheltenham, Gloucestershire, UK.
Posts: 3,077
|
Re: Q-meter wanted
Quote:
__________________
Regards, Jeremy G0HZU |
|
27th Feb 2019, 10:51 am | #19 |
Dekatron
Join Date: Jan 2004
Location: Newcastle upon Tyne, Tyne & Wear, UK.
Posts: 8,194
|
Re: Q-meter wanted
Hi, it appears that the OP was looking for comparative measurements, so that absolute accuracy is not required and frequency can easily be checked with a cheap frequency meter.
If the Q goes beyond the 400, then it is a simple matter to add a fixed resistor across the coil for measurement (that are again comparative). I did read an early WW article (20's I think) about special coils that had a peak Q of 5000, but were quite only stable for short periods of time. I'm not now sure what construction methods were used. Ed |
27th Feb 2019, 12:42 pm | #20 |
Hexode
Join Date: Mar 2009
Location: Cirencester, Gloucestershire, UK.
Posts: 391
|
Re: Q-meter wanted
Hello
The Electronics Australia, June 1969 Q-meter design looks very useful, and easily reproducible today. The full article covers six pages and a scan of this issue of the magazine can be found at: https://www.americanradiohistory.com...stralia_AU.htm best regards ... Stef |