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 Previous: Surfin': Hamming Outside of the Box |  Next: NTIA Study is Bad News for SAVI 425-435 MHz Proposals |
By Stu Cohen, N1SC
QST Technical Editor
October 30, 2002
Okay HF enthusiasts... do you think that you have a "compact" antenna for your favorite band? Let's see, a wavelength in free space at 30 MHz is about 33 feet; a practical 10 meter, ½ wave dipole being about 16 feet long. How about an antenna for a band where a wavelength is about 1 mm or .04 inches? That's just about what it is at the 241 GHz amateur band!
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The conference was international in scope; here's Grant Hodgson, G8UBN's presentation. | Matt Reilly, KB1VC's talk about building a "portable" EME dish. Look carefully at that title! |
I was impressed. After attending the Joint Conference of the 17th Annual Microwave Update 2002 and the 28th Eastern VHF/UHF Conference in Enfield, Connecticut on October 25 through 27, I came away with the realization that this is an enthusiastic group of hams who take our microwave bands very seriously.
The conference had 165 attendees. Every US call area was represented; in addition, there were several VEs, Gs, JAs, an ON and a VK.
The papers covered several areas and, among others, included those dealing with weak signal enhancement DSP software, improved local oscillator performance at microwave frequencies, antennas for 47 GHz, construction of a portable microwave EME (Earth-Moon-Earth) system, VHF and UHF transverter design, amateur equipment for the 241 GHz band and the use of TV satellite dishes (TVRO) for a massive, world-based, phased-antenna SETI (Search for Extraterrestrial Intelligence) project.
The weak signal DSP amateur-developed software is truly impressive. Imagine being able to recover signals well below the receiver noise floor... signals that can't even be seen or heard, yet amazingly result in Q5 copy! It puts EME and meteor-scatter communications within the modest equipment range, thus opening this exciting VHF-UHF communications area to many more amateurs. Kudos to Leif Asbrink, SM5BSZ; Bob Larkin, W7PUA; Joe Taylor, K1JT, and many other amateurs for development work in this area.
A paper relating the work done by Brian Justin, WA1ZMS/4 on the 241 GHz amateur band really spoke to millimeter wave communication. WA1ZMS/4 and Pete Lascell, W4WWQ have set a world DX record on this band with an 11.4 km contact. They have further modified their equipment to produce output at 322 GHz, producing a 0.5 km record at that frequency. They use Gunn oscillators, Schottky diode triplers and phase locked oscillators, producing 750 microwatts (that's ¾ of a milliwatt!) at 241 GHz. Not a lot of power, but at these frequencies, RF power is not easy to come by. Here, careful system design makes all the difference, especially when dealing with a path loss of over 160 dB, even at these (relatively) short distances.
 A small millimeter-wave portable station. |
Another talk by Paul Drexler, W2PED outlined the results of a project designed to produce a series of 24 GHz, 1 W power amplifiers. That project eventually succeeded in serial production of units that produced about 1.4 W of saturated output power. It will result in the production of about 40 units, giving some "crunch" to users of this band. By "users," I don't mean to imply that communication at these frequencies is routine.... there is no commercial gear available to plug in and operate. These are experimenters, in the truest sense of the word and the amateur spirit.
Several periodic auctions at the conference produced interesting bids for microwave oscillators, 10 GHz power amplifiers, circuit components for microwave signal chains and mixers, millimeter-wave dishes and other esoteric items. Additionally, an ongoing noise figure (NF) measurement lab yielded some amazing results for homebrew equipment. It was impressive to see noise figures consistently below the 1.0 dB figure at VHF and UHF. A homebrew 1296 MHz RF preamplifier having 23 dB of gain showed an outstanding NF of 0.23 dB. There's serious work being done here!
An interesting and exciting conference... a lot
has changed since those early days of modulated oscillators and 417A
preamplifiers at 432 MHz and my hat goes off to those amateurs experimenting
with and operating at, these frequencies. It is pioneering work indeed!
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Noise figure measurements at various frequencies gave participants valuable data. | A view in the parking lot: VHF/UHF antenna farm... mobile style! |
| Previous: Surfin': Hamming Outside of the Box | Next: NTIA Study is Bad News for SAVI 425-435 MHz Proposals |
