On Thursday, February 20, 2003, Neil, AB4YK, posted a message on the Microwave Digest reflector [Microwave@wa1mba.org] requesting advice on achieving at reasonable cost, the building of a 300 GHz plus communications system.
The objective is to generate and receive RF signals in the 300 GHz plus range. I requested inputs on the key steps and a description of people’s experiences. This is not a finished document.
The following helpful and informative ideas were received within just a couple of days from the group (not in any particular order). There’s a huge head of steam here. This field is going to break wide open, fast, given all the talent that’s being harnessed here. There’s lots of lovely spectrum to play with in spite of the atmospheric absorption which is graphed here. I have inserted comments here and there in the submissions that follow, I hope it doesn’t take away from the innovative ideas being presented here.
For terrestrial communications, the absorption by the atmosphere is of over-riding importance at these frequencies.
Jeff Kruth, WA3ZKR, pointed out that there’s essentially no stuff on the surplus market. So, I should figure on building my own multipliers and quasi-optical mixers. He figures it shouldn’t take more than $25-50 K to get something crude on frequency.
[NS notes that $25-50k is out of the price range. But see what Brian Justin and Luis Cupido have done with a lot less. Then there’s JC Bose who demonstrated 60 GHz experiments at London’s Royal Institution in 1897 (not a typo-that’s 1897). BTW note that the Royal Institution is not at all the same as the Royal Society. Back to Jeff Kruth.]
A friend of Jeff’s built a 300 GHz and a 600 GHz radiometer system in the early '60's for Uncle Sam. To get to 600 GHz with an LO, he said he just took a 300 GHz Carcinotron signal and doubled it". The LO life was rated for 20 hours and cost $15,000, waaay back when they had a running time meter on it and when they made a tune up, he got every thing ready then flipped on the B+ and quickly made a test, then shut the tube off! The carcinotron (O type BWO?? or M type, Jeff forgets!) was made by CSF in France. [NS’ note: I found a reference to a Thompson Carcinotron at one of the microwave EPR spectrometer web pages].
Jeff notes that the IEEE archives may include the tale of "Victorian MMW" where Dr. Chandra Bose demonstrated MMW signals at 60 & 100 GHz before the turn of the 20th century to the Royal Institution in London. He did it by spark-excited resonators, and got so much power that his parallel plate transmission line was glowing (plasma discharge) and the standing waves could be seen in the darkened room.
Another suggestion was to try heterodyning long wave near IR lasers in a non-linear medium, use radiometry methods for detection and send CW.
Jeff repeats: Aint gonna be cheap! On test gear Jeff notes that Brian Justin worked with an outfit that loaned him enough stuff to do it.
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Luis Cupido, CT1DMK, referred to his article presented at the MWU2001 describing corner cube mixers and etc .... That stuff gets you beyond 400GHz. A lot of patience is needed to get it all working. A good mechanics workshop is more useful than test equipment.
For test equipment Luis recommends using traditional generators (up to 18GHz or 26GHz) and spectrum analyzers that allow external mixers. The rest is DIY because there isn’t much stuff available. Luis has had good results at 411GHz.
The only decent way to begin is that you start building yourself a harmonic mixer and a multiplier. We don't need any degree of accuracy for a start.
Luis’ initial experiments were made with multiplier and harmonic mixer one just after the other. He could see about 80dB of attenuation. With +15dBm at 34.250GHz this was multiplied times 12 to give 411GHz and then a harmonic mixer down a few MHz that he could see on the analyzer at -65dBm.
The LO for the harmonic mixer was at 34.251GHz so the 12MHz signal could only be the 12th harmonic conversion. Luis is about to write a small article about these experiments.
(the mixers were published at the MWU2001).
Luis did all this on a very small budget and Jeff Kruth, WA3ZKR helped with the first experiments. The MWU proceedings show a photo of his first experiments... the big brick in the picture (is bigger than an ordinary mw-brick) it is a VARIAN 34GHz multiplied source (not a PLO) he got from Jeff at E-bay for $50. Luis has a 10m QSO... not much of a record... but 100% ham stuff. He is moving the LO up to 65GHz for better performance on the multiplication and harmonic mixer.
John Miles, KE5FX, described the use of Tek 49x analyzers ($3K-$5K) cover up to 325 GHz with external mixers, but “the upper-end mixers are rare as hens' teeth.” Count on spending another $1K-$2K just for the 220-325 GHz mixer...
John notes that the radio-astronomy guys are generating these sorts of frequencies through photonic mixing techniques. See
for a good .PDF on this. Just aim two lasers tuned 300 GHz apart at a photonic crystal, for a 300 GHz IF.
There might be room to do this on the cheap with diode lasers and homegrown crystals. John recommends surfing the ALMA (Atacama Large Millimeter Array) site at http://alma.nrao.edu NRAO’s Darrel Emerson reports some information at http://www.tuc.nrao.edu/~demerson/ . Emerson’s remarkable report on JC Bose’s researches is required reading, it is at:
He also suggested researching the IEEE archives to find the tale of "Victorian MMW" where Dr. Chandra Bose demonstrated MMW signals at 60 & 100 GHz before the turn of the 20th century to the Royal Institution in London. Bose did it by spark-excited resonators, and got so much power that his parallel plate transmission line was glowing (plasma discharge) and the standing waves could be seen in the darkened room.
John Miles, KE5FX, also wrote about a Carcinotron which is a powerful BWO for 100-1000 GHz.
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John, W3HMS, noted that Bill, W3IY, has a new Millimeter Handbook from France that might have useful ideas - some of them in English.
Bill, W3IY, writes - I'm
certainly interested, but I think it's kinda an extreme step. Why aren't you interested in the other
bands, where real QSOs are possible? The trouble with the 300GHz stuff is
that it's hard to work anyone beyond the range of your voice.
I think you will have to be very lucky and come across some surplus equipment, and even then it will be difficult. WA1ZMS may be willing to help. I think he gets help from UVA.
Brian Justin, WA1ZMS/4 – wrote:
Since I'm one of only two hams, the other being DB6NT, that have claimed to have had a QSO on the 300+GHz "band" I feel I should at least tell you my thoughts. My work was done on 322GHz. That frequency was chosen because it was the 4th harmonic of an 80.6GHz Gunn source that was driving a diode multiplier to get me on 241GHz. I am able to get about 750 microwatts of power on 241GHz and much less than that at 322GHz. Since the multiplier is an anti-parallel diode pair, the even order harmonics are suppressed. A properly design multiplier for 322GHz should be able to give you at least a few mW of power provided that you can drive the device with enough power.
As I understand it, the DB6NT approach to the question at hand, is to drive a single ended diode multiplier with a signal in the 30 to 40GHz range and live with the resulting comb output. Pick off the desired harmonic and you have a rig for the sub millimeter wave bands.
Industry standard waveguide goes as high as 325GHz with WR-3 and can be bought from Custom Microwave in Boulder, CO. The cost however is over $10 per inch. I know. I bought some. Higher than that and your on your own. Several sub-millimeter wave companies have their own "standards" for higher frequencies. The folks at the NRAO are a good example.
The mixer/multipliers I own for 241GHz and up are units that I helped modify-test-manufacture with the generous help of the guys at Virginia Diodes Inc. They are a spin-off off the Univ. of Virginia who also has helped me along. These guys are into mm-wave R&D and have a great semiconductor fab on campus just to make GaAs diodes. I do work for them, and in trade the have let me get a few of the "scraps". The commercial costs for such mixers are in the several K-dollars each. The 80GHz Gunn sources were semi-homebrew. I found some 40GHz Gunn diodes listed for sale from a scrap dealer in the UK. (RSGB news letter) Placed the diodes in a 2Fo mode Gunn cavity I bought from Harmonix Corp. and have a couple of nice 40mW Gunns on 80GHz.
It all took me over a year of solid work to get it all together. Home brew 6" dishes, phase locked Gunn sources, converting a 240GHz multiplier into a mixer, etc...
If I can do it, anybody else can. But I started out on 47GHz and have worked my way up. I'm sure that Will, W0EOM can tell you the same thing. You need to start out with lower freq higher power sources and multiply from there. Direct power on these bands can be done, but is more of a "lab thing" rather then taking it all roving with you to a snow covered mountain top.
But do look at the atmospheric losses on these bands first. I think you'll find that in order to do >1km you'll need several mW or relatively large dishes to get the job done. Losses can be several dB per km on these bands.
If I can answer any questions, just ask away. Also see: www.mgef.org for more info on the gear I built.
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Will Jensby, W0EOM writes from Santa Clara, CA:
and the group - this is a subject near and dear to my heart, as many
know. I am glad that Brian went first, as I have been following him on
My goal is to get to 241 GHz and be the second one to make a contact on that band. Since I have contacts on 76, 120 , and 144 GHz, and a drawer full of millimeter stuff, I hope to do it some day - over 300 GHz will come later.
Bob and I did make 25 km on 144 GHz about two weeks ago, with the best surplus Hughes mixers and multipliers we have been able to find, searching for over two years. Which in my mind, makes Brian's effort even more outstanding at 79 km.
I have built one of DB6NT's 241 mixers, but not sure I have a multiplier good enough to test it. I have seen a signal from a 215 GHz Impatt osc so am close.
Don't give up the effort to get to 300 GHz, but its not easy or cheap. I would likely pay over $500 for a mixer that works on 241, ones I have found so far are over $2500.
Gary Lauterbach, AD6FP, has been working toward 240/300 GHz capability and has collected the parts. The critical part was getting diodes capable of sub-mm operation. The group at NMRC sold him 5 honeycomb diodes (X81) at $100 apiece. The diodes can be used in open structure mixers through 2.5 THz. He also has 5 varactors that should be capable of several mw at 300 GHz.
A good reference on mm and sub-mm mixers is the mixer book by S. Maas, also check out his web site: http://www.nonlintec.com/. Maas is one of the well known experts in this field.
Jon, W2MXW, has decided on a homebrew approach including make/machine your own
mixer blocks, corner cubes, etc. and use scrounged parts. Some kind souls on this reflector have provided materiel for the cause as well. You can also get stuff machined to your specs and reasonably priced from (note: I have no affiliation therewith) www.emachineshop.com Forget the rare/big bux commercial stuff, you can do it (relatively) cheaply, with ingenuity. For LO/RF sources, try to get a surplus Gunn osc. at as high a freq. as you can find and injection lock it, or, use a brick and multiplier (for example one of my experimental setups is:
12.5 GHz brick->tripler [~37.5 GHz]->corner cube harmonic mixer (8th harm. on up is 300 GHz-up).
If you can get one of those surplus 20-someodd or 38 GHz units to use for your osc. or if you already have capability to provide a stable sig on 24 GHz or higher you're ahead of the game.
I'm also working on getting on 1000 GHz (1 THz) -plus. Investigating BWOs, mixing lasers too (on a semi-related note, also working on stabilizing laser diodes for heterodyne mixing for work at optical freq., another 'passion' of mine :-) SHF Micro sells low-cost Schottky mixer diodes which when removed from their ceramic pills can be used in the corner cubes with a catwhisker, or as-is in lower-freq. mult. or mixer stages. There is a (relatively) low cost commercial source for the 'honeycomb' diodes too. Tiny, delicate things so invest in a dissecting 'scope so you can see what you're doing. MIM (metal-insulator-metal) diodes can also be homemade, but are rather unstable (like galena detectors in xtal sets!) Some of the Schottkys and MIM diodes can operate up to optical freqs!! In all cases (except maybe spark, hihi) power will be very low, but still useful. You will be in the QRPpppp region with microwatts or at best a couple mW. Don't hope for watts or even dozens or 100's of mW. Fortunately antenna gain will help take care of that and is very easy to come by this high up. Greatest limitations on range are probably poor NFs and atmospheric loss. Humidity is your enemy so QSOs are best attempted when dry. *grin* Have played with spark too (above 300 GHz not [yet] allocated so FCC prohibition of Class B emission doesn't apply). Easy to use waveguide, perforated metal screens (yes, filters that actually work as EM "filters"!), and various other materials to ensure you really are on the desired bands.
Mercury vapor and some metal halide lamps also provide broadband energy in this region, useful as noise sources and for molecular spectroscopy, if that's your cup of tea! Crude detectors are made of homemade point-contact silicon or MIM diode in a parabolic reflector. A form of the latter is what J. C. Bose used (the "iron point contact detector"). Fascinating stuff. The main problem from my perspective is that AFAIK there isn't anyone near me interested in this stuff so I have to make TWO of everything if I expect to have a QSO! I'm working on a site compiling all the mmw/far IR info I've collected on the subject over the years (quite a bit of it, too!), but it'll be awhile yet before it can go online (time constraints, you know the drill).
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Bob Wesslund, WŘAUS, is working his way up in frequency. He has equipment up to 24 GHz for use on an antenna range. He uses an avalanche diode to generate 10 GHz signals. The avalanche diode has the advantage that it can be amplitude modulated with 1000 cps for a range. For 24 GHz he uses an Avalanche diode that is am modulated. Both of the units came as surplus for motion detectors for missile silos. For 47 GHz he has a 23.5 GHz Gunn diode and is looking for a pin diode modulator and a doubler for 47 GHz.
Web pages of interest:
IEEE MICROWAVE AND GUIDED WAVE LETTERS, VOL. 4, NO. 2, FEBRUARY 1994 37 “A 335 GHz Quasi-Optical Schottky Receiver” by Walid Y. Ali-Ahmad, Memberj IEEE, and Gabriel M. Rebeiz, Senior Member, IEEE
Nuclear Instruments and Methods in Physics Research A 436 (1999) 430}442
A new frozen-spin target for 4p particle detection
Ch. Bradtke, et al
In the GDH-experiment a carcinotron (Thompson CSF) was used as microwave source. It
provides a power output of 3.5W and its central frequency of 70 GHz corresponds to the electron Larmor frequency at a magnetic field of 2.5 T.
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AND NOW THE ALTERNATE IDEAS
Alternate approaches (inspired by 300 GHz+ thread)
Here in Canada we have no mode or bandwidth restrictions in the microwave & mm-wave bands (as long as you stay in the band) so I also gave some thought to spark as a cheap way to get some power on the mm-wave bands (we don't have bands over 300 GHz here though special permission could probably be obtained). It got me reading some VERY old textbooks !
There seems to be a problem of efficiency, however. Since the oscillation dies out after a number of RF cycles (about equal to the Q of the cavity) you need to keep repeating the spark to keep power coming out. However, if you do this at an audio rate as was done in the early days of radio, a millimetre-wave spark transmitter has zero output nearly all the time
(because of the large ratio of carrier to modulation frequency). Furthermore, I would expect the peak power to be limited by the small size of the cavity, so it might be hard to get much average output. Perhaps microwatts, like WA1ZMS, but the signal bandwidth is so wide it would likely get lost in the noise. I haven't really given a lot of thought to the use of a much higher modulation (spark repetion) frequency, say tens of MHz, but that might offer some chance if the arc could be extinguished fast enough.
It seems to me that there must be some room for amateurs to use techniques which are not suitable for commercial use to avoid the cost of diodes and other mm-wave devices. We are prepared to sit and tweak constantly (some of us prefer to, I think)which is totally impractical for most "real" applications.
One idea that got me thinking was running across some papers which showed experimental results of using ordinary garden-variety neon bulbs as X-band detectors...they actually worked quite well, but there was no info regarding other frequencies. They would go well with a spark transmitter...no diodes, transistors, nothing solid-state at all ! I was once told that there was such a thing as a ferrite multiplier...maybe we could learn how to make one using bits of ferrite from surplus isolators - no diodes needed ?
Jon W2MXW replied:
A quick Google search turned up these references for use of a glow lamp as mmwave detector:
see file "Neon lamp based scalar detector" mentions use of specially-constructed glow lamps as plasma diodes up to 100 GHz. Also has circuits for making your own glow lamp detectors. Well, off to the basement to have some fun!! :-)
Also, from same page "references" section:
N.S. Kopeika and N.H. Farhat, "Video Detection of Millimeter Waves with Glow Discharge Tubes," IEEE Transactions on Electron Devices, Vol ED-22, pp.
534-548, August, 1975.
N.S. Kopeika, B. Galore, D. Stempler, and Y. Heimenrath, "Commercial Glow Discharge Tubes as Detectors of X-Band Radiation", IEEE transactions on Microwave Theory and Technology, Vol MTT-23 pp. 834-846, October, 1975.
N.S. Kopeika, "Millimeter-Wave Holography Recording with Glow Discharge Detectors," Int. J. Electronics, Vol 38, pp. 609-613, May, 1975.
Also mentions sensitivity of 10 GHz (X- band) neon bulb detectors, ranging from 40 uV (best case) to 137 uV (worst case). Common NE-2U (should that be "-H"?) rated at 77 uV.
Jerry, K0CQ, writes:
I remember discussions on the R390 page in past years about the radioactivity tags on military versions of 0A2. Seems they need a bit of light to trigger reliably, and tube type military radar in pressurized enclosures for high altitude aircraft don't supply any light to the 0A2, so the 0A2W has a bit of radium or similar to provide a trigger.
Maybe some of the variation in neon sensitivity (besides individual variation on neon pressure) could have come from radioactive particles in phosphor coatings. Those might vary from production run to production run depending on the cleanliness of the phosphor chemicals.
Perhaps the neon RF detector could use a bit of tritium adjacent to the envelope to increase its sensitivity. I presume they do a DC bias. Maybe an AC bias, ala super regeneration could be used. Maybe some sort of modulated light bias... And since I've NOT read the references, I may have just reinvented all their techniques.
Do they still use a bit of something radioactive in some smoke detectors? How about antistatic brushes (as we used to use on vinyl records?) Or is anything weakly radioactive a sure death to sales so it can't be bought any more? How about a WW2 surplus watch face with glow in the dark numbers? There's a bit of radioactivity in the chemicals in some gas lantern mantles.
Entire content of prior 4 paragraphs is copyright of Dr.
Gerald N. Johnson, electrical engineer.
Reproduced by permission with thanks.
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Zack Widup, W9SZ, notes as follows:
Bob Paddock is an old friend of mine. He's not a licensed ham but knows a lot about RF. He gets into the "weird science" aspects quite a bit.
A few years ago I did a few experiments for him with a circuit he designed using coils wound on special ferrite materials to utilize the Barkhausen effect to detect (in theory) scalar waves. It was quite fascinating. These were done at VLF frequencies.
Now I'm going to have to play around with neon bulbs/tubes as mm wave detectors!
Geoff Blake G8GNZ , commenting on Gerry Johnson’s note, writes as follows:
IIRC the ionisation source in the 0A2W was tritium, as was used in all versions of the 0G3/85A2 which was used in virtually all Tektronix 5XX series oscilloscopes. We used dozens of these (85A2's) where I then worked and we stored them unwrapped for space reasons. When our Radiological Protection Officer (my boss) discovered this, he had a fit with his leg up!
We then carried out an investigation and discovered that we would have to break some 2,000 of 85A2's and collect ALL the tritium trioxide (?) powder before we had even a minimal risk!
Of course, we developed a healthy respect for things that glow in the dark, even if they require the application of a 100Vdc or so before they do so.
I for one thought K2RIW's article excellent!
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From: "firstname.lastname@example.org" <email@example.com>
To: W1MBA reflector and others
Sent: Tuesday, March 04, 2003 7:21 PM Subject: [Mw] 322GHz DX...
We (W4WWQ and myself), pushed our 322GHz "DX" to 1.4km on March 4th, 2003.
W4WWQ 37-21-14.7 79-10-13.7 FM07ji
WA1ZMS 37-21-23.6 79-11-10.8 FM07ji
Dew Pt: -6.7C
Atmos Loss: 10.6 dB/km <---WOW!
We likely would have had better results if we had a day with a lower dew point. The QSO on the WA1ZMS end
was tough at best. Problems with frequency stability limited the application of weak signal software like Spectran, etc.. So good old fashion 5WPM CW and headphones were used. Since one station has a better RX mixer than the other (isn't that always the case!) Pete, W4WWQ had about 6dB of margin on his end while I had 0dB on mine.
The gear is the same that was used in the recent past for other 241/322 GHz QSOs. Photos of gear can still be found at www.mgef.org For this QSO the 80GHz drive level into the diode multiplier was reduced during RX to get a lower conversion loss.
I hope that others can get some gear running on +300GHz and give this DX record a smashing!
73, Brian, WA1ZMS/4
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Thanks to all the authors for their contributions. Some of the above notes are copyright to the authors and their permission should be sought before reprinting their contributions.