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Old 31st Dec 2017, 2:46 am   #21
Bazz4CQJ
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Default Re: The Best GDO Ever Made?

Quote:
Originally Posted by WB6NVH-GEOFF View Post
One major correction - The Measurements Model 59 Megacycle Meter has no association whatever with the Boonton Radio Corporation, which was (and is) an entirely separate company. Measurements was located in Boonton, New Jersey,
Yes indeed, I have been quite confused about that background. I see that there were at least six business's operating in Boonton in the '40's, all doing similar kinds of radio kit and that Model 59 was a Measurements product. Thanks for that correction. I know that Boonton Radio are still around but have not yet had chance to check out the other companies. I note that the AN/PMR10 was made by Stamford Electronics, who were not based in Boonton.

I may be wrong, but I'm guessing that none of the services are still using GDO's.
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Old 31st Dec 2017, 8:41 am   #22
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Default Re: The Best GDO Ever Made?

Measurements was bought by McGraw Edison and seems to have disappeared since, probably by the 1970's. I have a vision of employees moving around between the assorted test equipment firms in Boonton, New Jersey at the time. Measurements made the superb Model 80 signal generator, which many of us in the states used as our main bench generator on HF and VHF communications equipment, and later the 560-FM and the Motorola branded equivalents.

Boonton remains in operation.

While the Mesaurements GDO is usually considered the best, I also have the Millen version which I like, except that having the remote head on the Measurements is quite handy.

One version of the Measurements instrument came in a handsome purple velvet lined carrying case with all possible measurement heads and coil sets. I was never lucky enough to find one.

The contract for the PRM-10 military GDO was not that large and thus they are not all that easy to find today, although they are a nice instrument as well.
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Old 1st Jan 2018, 4:24 am   #23
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Default Re: The Best GDO Ever Made?

I've been busy converting the PMR10 schematic to Brit convention. So attached are;
  • Model 59 (Brit)
  • PMR10 (Brit)
  • PMR10 (original)
That original PMR schematic takes a little time to unravel, and I'm not yet sure it's 100% right. It seems to show that the PMR is based on the model 59, but the PMR has the pot ganged with the tuning capacitor and has three resistors mounted in each coil assembly and the values of those change with frequency. Considering that the 59 was highly rated, someone seems to have gone to a lot of trouble to develop the PMR derivative!

B
Attached Files
File Type: pdf Model 59 Megameter (Brit).pdf (41.8 KB, 49 views)
File Type: pdf AN-PMR10 (Brit).pdf (63.5 KB, 41 views)
File Type: pdf pmr10 original.pdf (25.2 KB, 36 views)
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Old 1st Jan 2018, 1:32 pm   #24
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Question Re: The Best GDO Ever Made?

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Originally Posted by Bazz4CQJ View Post
My own FET-based unit does strange things when using it to trim aerials to length. It dips at frequencies which don't make sense and the dips are different (strangely narrow) from its normal behaviour.
[Quote slightly edited for brevity].
I assume that you are aware that the extent of the physical coupling from a GDO coil to the cct. under test (in your case, the aerial) will have an impact on the indicated resonant frequency?

Al.
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Old 1st Jan 2018, 2:09 pm   #25
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Post Re: The Best GDO Ever Made?

GDOs needn't be complicated affairs: I built this one years ago - it still works just fine.

Al.
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File Type: pdf GDO PW_July_1966.pdf (785.3 KB, 102 views)
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Old 1st Jan 2018, 3:52 pm   #26
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Default Re: The Best GDO Ever Made?

Hi Al, yes I assembled a little rig where I could easily move the FET GDO nearer or further away from the loop which fed the aerial, I guess that ideally, the minimum coupling which gives a visible reading should be used, but there were times when I was still concerned with the results.

Your own GDO is a classic valve one, the major difference from the American ones being discussed is the valve itself.

At the moment, I'm working on building a clone of an early Heathkit design which used a tunnel diode as the oscillator; interesting, but I note that it was not in production for very long. Then I think I will probably build a clone of the model 59 (I have a small number of Acorn valves to play with). Not sure about the PMR-10.

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Old 1st Jan 2018, 10:38 pm   #27
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Default Re: The Best GDO Ever Made?

Please don't hate me for this. I'm guessing that to you all GDO is a Grid Dip Oscillator? To me it's a Garage Door Opener!
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Old 1st Jan 2018, 11:52 pm   #28
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Default Re: The Best GDO Ever Made?

Not quite right for Amateur and Military radio, but is is the festive season.
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Old 2nd Jan 2018, 1:26 pm   #29
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Default Re: The Best GDO Ever Made?

I've also seen the abbreviation 'GDO' used to refer to a Gate Dip Oscillator - which, as an applied abbreviation, I'm none too sure makes sense.

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Old 2nd Jan 2018, 7:05 pm   #30
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Default Re: The Best GDO Ever Made?

In Heathkit's tunnel diode based dip oscillator, which I'm cloning, the dip is measured in terms of a change of the voltage on the tank circuit, sensed via a small (3pF) capacitor. Guess that will be either just a DO, or a TDDO.

I see that there is a lot of effort currently going on to incorporate tunnel diodes in to the gates of FET's, hence TFET's. Glasgow University are currently publishing papers on TD's; curious.

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Old 9th Jan 2018, 11:11 am   #31
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Default Re: The Best GDO Ever Made?

Just curious as to why - in the 'Magacycle Meter' - the anode load resistor is made up of three in series - R10 (6K8), R15 (6K8) and R14 (5K6), totalling 19K2. Why not just a 20K resistor (+4%), which would have been a standard value at the time, or 2 x 10K? Just seems a bit ungainly to use a string of 3 resistors in series for no apparent reason, either technical or practical unless I'm missing something. Even 18K or 22K would surely have been fine - the anode voltage wouldn't have been that critical and would have no bearing on the performance or accuracy.

Back in the 1980s when I was active in amateur radio, I built my own antennas - a G4MH type mini beam, multi-band trapped verticals and trapped dipoles, for which I made my own traps. In 1985 there was an excellent PW article to make an FET Gate Dip Oscillator which covered from 1.8 MHz to 150 MHz in six overlapping ranges using home-wound plug in coils. The article had full constructional details, and there was a follow up 4-page in Dec 1985 on how to use a GDO.

http://www.americanradiohistory.com/...PW-1985-10.pdf

http://www.americanradiohistory.com/...PW-1985-12.pdf

I've attached some pics of the one that I built, which I was able to calibrate using a home-brew frequency counter. It worked very well. The last pic is of a 7 MHz trap I made for a trapped dipole using fibreglass spreaders to space the coil, and double sided PCB laminate for the 22pF capacitor. When adjusted using the GDO, the traps were housed in plastic tubes and sealed. The traps and hard drawn copper wire was up in the air from 1986 - 2003 when I took down all my antennas and called it a day.

The first pic shows the GDO with the six coils and a 7 MHz test coil.
Second pic shows the VHF coil at 150 MHz displayed on my homebrew PW 'Robin' frequency counter.
(Designed by the late Mike Rowe (AKA 'Swordholder', the original designer of the Sussex Valve Tester).
Third pic is the RF 'sniffer' attached to the Robin, sniffing the VHF coil.
Fourth pic is a display of 15 MHz RF from the GDO.
Last pic is of a 7 MHz trap, yet to be housed.

(From the pic of the trap, it may seem that both ends of the coil are soldered to the same side of the PCB capacitor, creating a dead short across the coil. That isn't so - there is a groove on each side of the PCB towards each end, obscured by the wire. The grooves create and area of copper on each side of the PCB, which - along with the fibreglass laminate - form a capacitor which will carry the full legal limit of 400W SSB).

All good fun at the time.

Back to the Acorn valved 'Megacycle meter' there was an article in Short Wave Magazine back in March 1957, which can be found here:

http://www.americanradiohistory.com/...WM-1957-03.pdf

Nice things to own, as curios and relics of a bygone era, but I wonder if anyone uses GDOs these days, and if so, what for, in a 'plug 'n play' era when antennas come from shops?

Hope that's of interest.
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Old 9th Jan 2018, 11:56 am   #32
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Default Re: The Best GDO Ever Made?

Self capacitance in series?

Lawrence.
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Old 9th Jan 2018, 12:50 pm   #33
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Default Re: The Best GDO Ever Made?

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Originally Posted by David G4EBT View Post
Nice things to own, as curios and relics of a bygone era, but I wonder if anyone uses GDOs these days, and if so, what for, in a 'plug 'n play' era when antennas come from shops?
I like GDOs even to this day. They're cheap, simple and very useful. I've got a Heathkit GD-1U which is a little drifty and limping slightly, missing one coil and someone has added a BNC connector for a counter but it still works fine.

I tend to use mine for testing resonant circuits and for filter sweeps, adding my FET voltmeter and RF probe and my counter plugged into it. Also have used mine for ballparking inductor values. Less so as it's a bit difficult to use one with toroidal cores.

I have been meaning to build my own for a while and have most of the parts as specified in that PW article so might just have a go there.

As I'm currently doing my Foundation stuff, I will be building antennas soon past the simple dipole I have already slung together so will be very useful. I'm not going for the easy path which is "buy an MFJ antenna analyser and plug a Yaesu into it" although that's what I suspect the foundation course tutors would like as they sell them. That would be boring.

As always David, I am rather impressed by your creations

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Old 9th Jan 2018, 3:15 pm   #34
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Default Re: The Best GDO Ever Made?

Antenna experimentation and construction is perhaps the most satisfying aspect of amateur radio, and one where home-brew is still a real practical proposition. The present licence structure and training to become a radio amateurs is in my view, far more comprehensive and much better preparation than the old 'essay style' RAE that I took back in 1974. The Foundation Licence is the only one that stands on its own. The Intermediate and Full licence 'bolt-on' to the FL. All involve practical work and on air QSOs, none of which applied under the old set-up.

I've attached a pic of the trap in my previous post, housed and ready to install. Second pic is on a home-brew 1:1 balun for a trapped dipole that I made, wound on a 1/2" ferrite rod, and the third pic is of another balun, using two 12mm ferrite rods side by side, glued together. Cost next to nothing to make and didn't take long either, so why do people fork out for commercial items when they're so simple to make? (If I said my hobby was marquetry, and I bought all the items ready made from a shop, people would think I was nuts!).

Good wishes in your endeavours.
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Old 9th Jan 2018, 4:54 pm   #35
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Default Re: The Best GDO Ever Made?

A balun is first thing on the list of antenna parts to put together so that's rather helpful. Very neat construction. I like the absence of a recipe involving Amidon parts, which are the bane of my existence as I never seem to have the right one. I've started winding air cores. Turns out they're much more stable, and on topic, considerably easier to poke around with via GDO anyway! Thank you again for your comprehensive post.
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Old 12th Jan 2018, 10:03 pm   #36
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Default Re: The Best GDO Ever Made?

Ah! Just spotted the later posts here. Re the three resistors in the HT line of the Model 59 (Megacycle Meter); I cannot offer any comment on the rationale of the two 6k8's. The separate 5k6 allows a tapping which relates to the fact that the 59 will also act as a wavemeter, detecting RF signals and indicating them both on the meter and via headphones.

The manual for the 59 describes how it can best be used in various roles as a GDO (including antenna work) and also as a means of measuring L, C, Q and mutual conductance. Sadly, it's over 3MB so I cannot upload it.

As stated above, I built a FET GDO back around 1970 but there have been times when it has given spooky readings which were hard to explain, most recently, when playing with a 5MHz dipole. If you spend time Googling "GDO's" (which I have ) you find questions here and there about FET GDO's (and Wrangler has expressed similar concerns). I think some people believe that a valve may be better, or even a bipolar transistor, but I'm not stringent on this; whatever rocks your boat! I am interested in building another GDO, I'm now cooling off the tunnel diode option and heading towards an Acorn, perhaps a direct copy of the Model 59.

B
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Old 12th Jan 2018, 11:30 pm   #37
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Default Re: The Best GDO Ever Made?

The link I mentioned in post #17 has the original manual as mentioned by Baz as well as the military manual.

One problem I foresee in trying to replicate the Megacycle meter head assembly is 2x 50pf coil coupling caps. See the schematic in post #1 for reference. These are not conventional wire ended parts but are made up of brass parts of the capacitor assembly sandwiched together with a dialectric between them.

Al
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Old 13th Jan 2018, 9:27 am   #38
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Default Re: The Best GDO Ever Made?

Mmm, I'd noted that the tuning caps, the Acorn base and the coil sockets were assembled as a single entity, but hadn't spotted the two caps to be mechanically fabricated and part of that entity.

I'd be quite happy if my version would operate to ~150MHz, rather than 430 (?) MHz of the original, so I might get away with a good but more conventional assembly?

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Old 13th Jan 2018, 10:03 am   #39
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Default Re: The Best GDO Ever Made?

Just a point on spooky readings on FET GDOs; I’m wondering if this is the same thing I had with my VFO based on a 2n4416. I found after looking closely with the scope is that it would periodically break into bursts of oscillation. So it was oscillating at the fundamental and a high frequency that was modulated by a third. Couldn’t see it on an analogue scope but could on a digital. Ferrite from a broken tek scope slipped over gate stopped that but I’m not sure that would scale to a wide band oscillator like a GDO without tailing off.
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Old 13th Jan 2018, 12:03 pm   #40
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Default Re: The Best GDO Ever Made?

You need wiser man than me on this. What drew me up was the work that Al did on the wideband FET amp which he did manage to finally sort out, but only after a little angst. One member of the forum was doing SPICE modelling for him and saying things like "the FET gate goes into negative resistance under these conditions" . It was at this point that I got my coat.

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