K-W Radio Amateurs Since 1922
to 24 GHz
by Steve Kavanagh
Based closely on a paper originally
published in the "Proceedings of
the 51st Annual Meeting of the Southern Ontario VHF and UHF Group", Toronto,
June 16, 2001
(prices quoted in article are as
of summer 2001)
in Ontario on 24 GHz is starting to increase. This
article provides a guide on how to join this activity and what to expect.
frequency allocation is as shown in the following table, along with the
other services that share this band in Canada. Unlike
some of the microwave bands, this band is available worldwide.
|Amateur (Primary), Amateur
(Primary), Amateur (Secondary), Earth Exploration Satellite -Active
really isn't heavy usage by the other services at present, except for the
unlicensed ISM equipment in the form of low power radar burglar alarms
and door openers. Parts for this
ISM equipment have become available as surplus, helping amateurs to get started.
propagation characteristics at 24 GHz are quite similar to the lower microwave
bands in most respects. That is to
say that the most useful propagation
is line-of-sight, with occasional enhancement by Tropospheric bending and
ducting, and perhaps some Tropospheric scattering with the best available
equipment. I've not seen any claims
regarding rain or snow scatter, but I suspect it is possible with good equipment.
there is one significant difference, which is that the 24 GHz band falls
near the centre of a band which suffers from absorption by water vapour
molecules in the atmosphere. This
provides an extra challenge for those trying to cover distances of more
than a few kilometres. The following
graph shows the losses which can be expected through air at different temperatures
and with relative humidities from 10 to 100%. Since
air can hold more water at high temperatures the losses increase with temperature
as well as with relative humidity.
while line-of-sight paths are the ones we try when starting out, they usually
require portable operation. But during
the summer in southern Ontario, when we like to be outdoors, it is usually
both hot and humid which leads to high losses. For
example, from the graph one can see that at 27 degrees and 80% relative
humidity the loss is 0. 5 dB per kilometre. So
over a line-of-sight path of 50km an extra loss of 25 dB must be dealt with.
Tropospheric ducting and refraction
which can extend the paths beyond the horizon rely on variations of the
refractive index of the air due to its water content, and can become more
pronounced if the humidity is high. So
in order to get a long path we need to put up with lots of path loss !However,
the challenge is not insurmountable as shown later by some examples of
what can be done. If nothing else
it provides an incentive to do some microwave operating in the winter when
both lower temperatures and lower relative humidities prevail. That
same 50 km path at 0 degrees and 40% relative humidity suffers only about 0. 05 dB/km loss or
2. 5 dB in total. So
this path could be done on a typical winter's day with 22. 5 dB less power
(a factor of nearly 200 times less) than in July.
term "active" may be a bit optimistic at this point, but the bulk of 24
GHz operation in North America is concentrated in two groups. They
are the same as on 10 GHz:
FM voice (WBFM) using basically the FM broadcast standard of 75 kHz deviation
and IF bandwidths around 200 kHz, with transmit and receive frequencies
offset from each other by 30 MHz for full duplex operation, and normally
using vertical polarization, and
far, I know of no narrowband activity
in Canada with the exception of VE4MA's 24 GHz moonbounce efforts. For
the builder of equipment WBFM gear is much cheaper in parts and easier
to get going. If one is interested
in commercial gear, however, a transverter for narrowband operation is
actually cheaper than a full WBFM transceiver, if the cost of the 144 MHz
transceiver that the transverter works with is not included in the comparison.
wideband FM, VE3's OIK, VXO and SMA are active. VE3EZP
is working on equipment and W2EV quite often operates from the Canadian
side of the Niagara frontier. I understand
that VE6KKZ and VE6TC also have wideband gear for 24 GHz. There
is also some activity in the Rochester, NY area (certainly on wideband
FM, possibly also narrow band) and in Michigan (primarily narrow band).
modes (CW and SSB voice) which are used exactly as on the VHF bands, i. e.
upper sideband for voice, on-off keying for code, single frequency simplex
operation using horizontal polarization.
some areas of the world, FM television is used on 24 GHz. Denmark
probably has the most enthusiastic 24 GHz TV operators.
for wideband FM is all based on variations of the
"Gunnplexer" concept initially popularized for 10 GHz by M/A COM. These
use a 24 GHz Gunn diode oscillator as a transmitter and simultaneously
as the local oscillator for the receiver. The oscillator is frequency modulated
for transmission. The receive frequency
is offset from the transmit frequency by the intermediate frequency used. In
North America, an IF of 30 MHz is standard for 24 GHz operation. The
Gunn oscillator frequencies used are near the centre of the band, around 24. 125
GHz. Transmitter powers vary
typically from 5 mW to 200 mW.
following block diagrams show some of the possible versions. The
first is the simplest, which employs a Gunn oscillator/mixer unit as typically
used in alarm and door-opener equipment and is the approach used by VE3VXO.
mixer diode is simply mounted in the waveguide between the oscillator and
the antenna. The Gunn oscillator
is tuned simply by varying the supply voltage. At
this point it is appropriate to note that virtually all 24 GHz equipment
employs waveguide size WR42 with inside dimensions of 0. 42 by 0. 17 inches.
you are able to find a circulator, a more elegant approach is possible,
which better optimizes the power going to the mixer from the oscillator
and minimizes the received power which is lost in the oscillator.
a varactor-tuned Gunn oscillator is available, the modulating and tuning
functions can be separated from the Gunn power supply, resulting in more
optimal performance. This approach,
combined with the use of a circulator is used in the Advanced Receiver
Research TR24GA transceiver for which the block diagram is shown below. VE3OIK
has used a varactor-tuned oscillator in a similar design, but with a straight-through
I first acquired some 24 GHz oscillator mixer units (from Kustom speed
radars) I discovered that they could not be tuned more than 2 MHz using
the supply voltage, and they did not have varactor tuning. Since
the warm-up drift was at least 5 MHz there was no way that I could set
them reliably to be the necessary 30 MHz apart to be able to communicate
with each other. Therefore I adopted
a wide-range tuneable IF scheme as shown below and just preset the Gunns
to be about 30 MHz apart. The exact
necessary IF is found by tuning the IF up-conversion oscillator. It
is also worth noting that the Kustom units, occasionally found as surplus,
have an unusual waveguide junction which results in transmission with one
sense of circular polarization and reception on the other sense. For
two such rigs to work each other one must take care to have the opposite
polarization senses on the two.
of WBFM Equipment and Parts
quoted as of summer 2001)
only source of ready-to-operate equipment that I know of is Advanced Receiver
Research in Connecticut. Their TR24GA
transceiver, with a 25 mW output and a small horn antenna sells for US $699. 95.
They also sell the IF receiver/modulator
the homebrewer, Advanced Receiver Research offers the microwave Gunnplexer
(Gunn oscillator, mixer and circulator) for US$369. 60. SHF
Microwave Parts in Indiana offers a 5 mW varactor tuned Gunn/mixer unit
for US66. 00 (used by VE3OIK). They
also sell replacement Gunn and mixer diodes. Gunn/mixer
units also occasionally show up as surplus (though much more rarely than
the similar 10 GHz versions). VA3REI
was able to acquire one Gunn/mixer unit from an alarm company, which is
now in VE3VXO's rig,
and I found two Kustom radar guns at Electronic Surplus Industries in Toronto.
found pieces of a Kustom unit at the Rochester (NY) Hamfest. VE3EZP
obtained a commercial point-to-point 23 GHz radio (based on similar Gunn
oscillator technology) from a local ham in London and is attempting to
convert it to ham use at 24 GHz.
of WR42 waveguide, circulators and the like show up very occasionally at
surplus stores and major ham flea markets such as Rochester and Dayton.
picture below is of the Gunn/mixer assembly from SHF
for narrow band operation normally involves a transverter to downconvert
receive signals and upconvert transmit signals to a lower frequency (usually
144 MHz) CW/SSB transceiver. The
standard calling frequency for narrow band operating on both CW and SSB
is 24. 1921 GHz so transverters are designed to provide coverage of a narrow
band around this frequency. As I
have not tried it yet, I will refrain from providing details of typical
equipment. However, some excellent
ideas can be obtained from the Kuhne Electronic website as well as articles
in the German (but bilingual in English as well) publication DUBUS, many
of which are available on the World Wide Web.
for NB Equipment and Parts
only manufacturer of complete transverters that I know of is Kuhne Electronic
in Germany (run by DB6NT). They are
represented in the US by SSB Electronic USA in Pennsylvania who offer the
basic transverter for US$475. Rumour
has it that it is cheaper for Canadians to buy directly from Germany. DB6NT
also makes a line of low noise and power amplifiers which allow quite a
sophisticated rig to be put together. There
is some work needed to get it on the air; antenna transfer between receiver
and transmitter and interfacing with your 2m transceiver are up to you. The
majority of hams active on 24 GHz narrow band modes (worldwide) appear
to be using DB6NT transverters.
such as transistors, capacitors and the like, needed to build the more
sophisticated circuits in narrow band equipment are something of a challenge
to procure for the individual. Down
East Microwave in New Jersey has some parts. For
local oscillators, 8 or 12 GHz phase-locked loop "brick" oscillators can
be used with frequency multipliers using GaAs FETs, or diode harmonic mixers.
PLL bricks are often found at major flea markets and in surplus stores,
but rarely at exactly the frequency needed, so some retuning will likely
be needed. You will have to work
quite hard to find everything needed to build a transverter for this band
all 24 GHz operation uses either horn or parabolic dish antennas. These
are very much the same as for the lower frequency microwave bands, except
that the tolerances for dimensional errors are smaller. Dish
feeds always use waveguide input, a the loss in a coax feed from the back
of the dish to the focus is almost always excessive (0. 7 dB per foot in 0. 141” semi-rigid cable, for example) and coaxial connectors that work
at 24 GHz are hard to find.
at 10 GHz or below, the maximum dish size that can be used is usually limited
by unwieldiness in the case of portable stations or tower wind loading
in the case of fixed stations, at 24 GHz the difficulty in pointing the
dish is often the limiting factor. VE3VXO
has been using a 2 foot (60 cm) dish when portable and reports it to be
very critical to point (but very effective once aimed correctly !). The
figures below show the typical beamwidth and gain versus dish diameter
at 24 GHz.
of antennas are primarily surplus stores (Electronic Surplus Industries
in Toronto has supplied a number of dishes, a couple of which are in use
on 24 GHz) and ham flea markets. Ku
band satellite dishes should be accurate enough for 24 GHz use.
Results Can Be Expected?
in southern Ontario most of the wideband activity used only small horn
antennas until recently. The best
distance covered between two horns was 35 km (line-of-sight, from Baden
Hill near Kitchener to Bower Hill near Woodstock), using about 150 mW at
each end. This was, however, done
in quite warm humid weather. Distances
of up to about 15 km were quite easily worked. With
the addition of dishes the distance has been pushed up, first to 42 km
(one dish at about 10mW and one horn at 150 mW) and most recently to nearly
75 km between two dishes at 5-10 mW, between VE3VXO at Stoney Creek and
VE3OIK at Star, near Caledon. This
path is (barely) line of sight and was completed in March 2001, when the
water vapour attenuation was quite low.
frequency stability of the wideband rigs is not very good and generally
requires a hand on the tuning dial at all times. VE3OIK
has added automatic frequency control to his rig so that it tracks the
frequency of the received signal. This
has been found to be quite worthwhile.
band equipment can provide much better performance but the distance tends
to be limited by the water vapour absorption. NE8I
reports from Michigan that distances of more than 40 km over land, with
100mW and dishes, are quite difficult. A
100 km path across Lake Michigan has been worked but typically gives weak
signals with 100mW and 1m dishes. With
800mW output and dishes, WW8M and NE8I report distances of about 60 km
worked with very good signals this winter. Further
a field, in Europe and California, for example, where activity and mountains
are higher, longer distances are becoming quite common. Long
over-water paths of 200 - 400 km have also been worked on occasion, despite
the water vapour absorption.
following table summarizes a few distance records on 24 GHz. As
you can see, there is plenty of scope for improving the Canadian distance record.
are the articles on amateur 24 GHz equipment and operating that I know
of so far. I'm sure there are many
others that I haven't found yet.
- 1. J. N. Gannaway, G3YGF & S. J. Davies, G4KNZ, eds. , The Microwave Newsletter
Technical Collection, Radio Society of Great Britain, 1983 contains several
short articles on WBFM gear:
"A Power Supply/Modulator for the GDO33 24 GHz Oscillator
"Modifications to the GDO33"
"Notes on GDO33 PSU"
"An Improved 24 GHz Diode Mount"
"A 1N26 mixer for 24 GHz"
"Control of a Gunn Oscillator by Phase Locking Techniques"
Tom Hill, WA3RMX, "SSB/CW Equipment Concepts for 24 and 47 GHz", Proceedings
of Microwave Update '89, ARRL, 1989
Dennis Sweeney, WA4LPR, "Design and Construction of Waveguide Bandpass
Filters", Proceedings of Microwave Update '89, ARRL, 1989
Kent Britain, WA5VJB, "Horns for 10 GHz and Up", Proceedings
Update '89, ARRL, 1989
Tom Hill, WA3RMX/7, "24 GHz Low Noise Amplifiers", Proceedings
Update '91, ARRL, 1991
Kent Britain, WA5VJB, "Dual Mode Feedhorn for 24 GHz", Proceedings
Update '91, ARRL, 1991
Sam Jewell, G4DDK, "24 GHz and the East Coast Effect", Proceedings
Update '97, ARRL, 1997
Toshi Takamizawa, JE1AHH, "The Art of Building 24 GHz Equipment that Works",
Proceedings of Microwave Update '97, ARRL, 1997
John Sortor, KB3GX and Paul Drexler, WB3JYO, "Getting Started on 24 GHz",
Proceedings of Microwave Update '97, ARRL, 1997
DL3ER, "Waveguide for the 24 GHz Band", VHF Communications, Issue 4, 1980
DL3ER, "A Wavemeter for the Frequency Range
23. 5 to 24. 5 GHz", VHF Communications,
Issue 4, 1981
DC3QS, "A Gunn Oscillator for the 24 GHz Band", VHF Communications, Issue
DL6MH, "A Straight-Through Mixer for 24 GHz", VHF Communications, Issue
DL3ER, "A Gunn Oscillator, Detector and Mixer Module for 24 GHz", VHF Communications,
Issue 3, 1982
DJ7FJ, "Straight-Through Mixer for 24 GHz", VHF Communications, Issue 4,
DL3ER, "A Spectrum Generator for the 24 GHz Band", VHF Communications,
Issue 4, 1982
Emil Pocock, W3EP, "UHF and Microwave Propagation" in The ARRL UHF/Microwave
Experimenter's Manual, ARRL, 1990 [contains some useful info on water vapour
Michael Ross, VE2DUB, "24 GHz Gunnplexers", The Canadian Amateur, November
1986 [short description of Advanced Receiver Research equipment]
Juergen Dahms, DC0DA, "Einfaches Hohlleiterfilter fuer 24 GHz" [waveguide
filter], DUBUS Issue 1, 1989, pp. 7-8
Ulf Huelsenbusch, DK2VR, “24 GHz Baugruppen” [waveguide-coax adapter and
slot antenna], DUBUS, Issue 1, 1984, pp. 1-2
Michael Kuhne, DB6NT, "GaAs FET Doubler with Mixer for 24 GHz", DUBUS Issue
3, 1986, pp. 207-212
Michael Kuhne, DB6NT, “Transistorized 24 GHz Transverter, DUBUS Issue 1,
1988, pp. 3-11
Erich Zimmerman, HB9MIN, "SSB-Millimeterwellen-Baugruppen 24 und 47 GHz"
[multiplier/mixer PCB], DUBUS Issue 1, 1990, pp. 10-16
Toshihiko Takamizawa, JE1AAH, "24 GHz Transverter with
HEMT's", DUBUS Issue
2, 1991, pp. 37-48 and Issue 3, 1991, pp. 24-32.
Reed Fisher, W2CQH, "A Simple 24 GHz Bandpass Filter", Proceedings of Microwave
Update 2001, ARRL, 2001.
Joel Harrison, W5ZN, "Evaluating 23 GHz Commercial Feeds for Amateur Service",
Proceedings of Microwave Update 2001, ARRL, 2001.
Lars Karlsson, AA6IW/SM0CQC, "Six-Way Combiner for 24 GHz", Proceedings
of Microwave Update 2001, ARRL, 2001.
Barry Malowanchuk, VE4MA, and Al Ward, W5LUA, "The First 24 GHz Moonbounce
QSO", Proceedings of Microwave Update 2001, ARRL, 2001.
William D. McCaa, K0RZ, "Concepts and Approaches to Building 24 GHz Transverters",
Proceedings of Microwave Update 2001, ARRL, 2001.
Lilburn Smith, W5KQJ, "A Triband 3. 456, 10 and 24 GHz Transceiver", Proceedings
of Microwave Update 2001, ARRL, 2001.
Gary Lauterback, AD6FP and Lars Karlsson, AA6IW, "Dual-Band 10/24 GHz Feedhorns
for Shallow Dishes", Proceedings of Microwave Update 2001, ARRL, 2001.
Websites of Interest
SHF Microwave Parts Co. http://www.shfmicro.com/
Kuhne Electronic http://www.db6nt.com/
DUBUS archives http://dpmc.unige.ch/dubus/
Microwave e-mail reflector www.wa1mba.org
Microwave email reflector archives at http://www.infosite.com/~jkeyzer/uwave/
Advanced Receiver Research http://advancedreceiver.com/
G8ACE (24 GHz amplifiers) http://www.microwaves.mcmail.com/
SSB Electronic USA http://www.ssbusa.com/
Down East Microwave http://downeastmicrowave.com/
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