On the Shoulders of Giants

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11 April 2011 | by Fred WØFMS | Share | | Leave a Comment (1)

I really can’t believe I was invited to post here on AmateurRadio.com. I tend to be brutally honest and not very politically correct or savvy and I figured it was more likely I’d upset someone here than be invited to post.

I do already have a website (a bit out of date, albeit) and a blog (which I will reserve for lengthy and very technical posts or ones I don’t think are of general interest). But I will try to post here first. Lets make the best of it regardless, shouldn’t we?

Spring is very rough for me in the free time department. I have to “un-winterize” everything and do “honey-dos” and the antenna projects, and then other ham projects/operating which always seems to come last :(. So likely with my other ‘blog, you’ll see more in the winter than in the summer from me!

This weekend was typical Iowa in that the weather was actually very nice, but the threat of very violent weather and actually too strong of winds to do much productive work hurt the schedule a bit– pushed everything out another weekend… sigh…

Anyway, I digress.. I was asked by Matt W1MST to try to have some microwave, 1+ GHz plus material here. I have to be honest, I am a VHF+er by heart and most of my 25 years licensed, but only in the last year did I get decent HF antennas, so lately my interest is in HF and (even though I said I never would) contesting and paper chasing. I figure it’s time I tried it. So if any DX wants to work me or ND (ZERO in the ND QSO party, dudes, what’s up with that? I worked a bunch of rare DX that weekend but no ND? huh?), SD, MN, NV, WY.. e-mail me and set up a sked! 🙂 But I suspect that I’ll post mostly HF stuff for awhile. Help me get WAS and DXCC if you want to see more microwave stuff! (I’m sure VUCC would be next. Like I said “cocaine” would likely be a cheaper hobby!)

But for my first post I’m going to document something not invented by me nor even yet built by me.

Especially in Engineering, good engineers “engineer”, great ones “steal”. There are many “giants” in amateur radio.. the best thing we can do is build on their legacy.

Here is probably the least expensive way to get a couple of watts on 10 GHz. This amplifier was designed and built by Jerry Seefeld, WA9O who builds his own solid state QRO station on VHF/UHF and Microwave– several hundred of watts combined on each band, and runs it from the trunk of his car as a QRO rover! I’m not there and wasn’t when I roved. What can I say.. his stuff is seriously hard core and really, really good…

This is his 10 GHz amplifier: It turns out that the “FET” that is used in the Down East Microwave 10 GHz amp, is really a MMIC and has internal matching in it. The part is available from DEMI currently for $110, the part number is FMM5061VF, it’s a Eudyna (formally Fujitsu Semiconductor) part. It turns out that this device’s width is the same size as the width of two SMA’s mounted close together. Since the device is a MMIC with internal input/output matching, only biasing and simple grounding is needed to complete the amplifier.

With some very careful machining and a breadboarded negative bias circuit, this device can be used without a printed circuit board.

This is the view of the device mounted between two SMAs. Bypassing and grounding of the device is accomplished by “bubbles” in the copper tape and convenient soldering points.

Here is a view of the “top” of the amp:

WA9O 10 GHz Amplifer NO PCB, connector side

Here is a view of the bias circuit schematic. Comments from WA9O on this will be posted at the end of this blog post.

See WA9O's comments about the schematic later in the post!

And finally the business side of the amplifier with the bias board installed:

Here are Jerry’s comments about this circuit.
“The P channel IRF9530 has a 27K resistor not labeled in diag. This keeps the IRF9530 turned off when not grounded to xmit. The LT1054 has a voltage divider of two resistors to set the output to -5V. Kinda neat to have something to produce a neg supply and regulate it too. It’s good for 100mA but only 25mA is needed. The LT1085 is a 3 amp unit and if the power is applied by accident with the T/R in xmt then only 3 amps should hit the 5061 until the -5V builds up a milisecond later. It should be Fred-proof. The 5061 draws just under 2 amps regardless of B+ voltage. DEMI runs it at less then my 8.5V and they have been run as high as 10V but I don’t have the guts to run it above 9.0V.“
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See the “Fred-proof” comment, he must know me. It’s a very simple design… and I posted this for the first AmateurRadio.com post for a reason. First off, Jerry WA9O and I would like to say that all of the old “you can’t do microwave if you can’t machine to the thousandth” was never correct and is even less so with our modern, internally matched, broadband components. (Jerry has told me in the past I could forward on the design of this amplifier if I gave him credit! I’m giving him credit! It’s NEAT! I will build it someday when I get off the HF “high”).
All I can say is that idea, that things had to be built to commercial tolerances to work at microwaves– did more damage to that part of the hobby than anything else possibly could have.. thanks ARRL.
It’s like (exactly) being told you can’t work DX with your HF vertical and crappy ground system, you need a 70′ tower and a beam, so don’t bother with anything less. Well that’s nice but a lousy antenna is infinitely dB better than nothing. In most cases, your best tolerance machine work will work on VHF+ and it will just keep getting better with experience!
In this case, that 10 GHz amp, a DBS/DSS dish and a drilled out feed or a W1GHZ horn will put you into the “big boy league” on 10 GHz for as little as $200 for the amp, nothing for the dish if you are a good dumpster diver like I am, and maybe $300-$400 for a transverter, which, of course you will build yourself, right? And the bragging rights are always fun.. only you and the others who have done it will realize that the equipment is almost easy with modern components. Now working DX at 10 GHz is harder but it’s a really fun challenge and there are others out there who would LOVE to help you do some.
I’d like to encourage microwaves. And IMHO, 10 GHz is where it really becomes fun. There are so many cool things to do on ham radio.. and this is one of the more “cutting edge” aspects of the hobby.
Probably my next post will be another “giant” post (at HF though).. but this one I am building and hopefully will test. Check back here in a week or two for that!
73 de W0FMS

Fred Spinner, WØFMS, is a regular contributor to AmateurRadio.com and writes from Iowa, USA. Contact him at [email protected].

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