Hi, about two years ago, I started a design for a robotics class project of
a AZ-EL rotator controller system, and a hardware package for the mechanism
for rotating an antenna in any direction subject to mechanical stops. The
system would have been able to handle regular and flip modes. I didn't do
anything more than calculations, and moved on to building a classroom
instructional robot then.
Lately, as I am setting up (K3GWU, the George Washington University Amateur
Radio Club and Research Station) I find that the price of az-el systems
such as G5500 + Yaesu AZ-EL rotors are expensive, and are not typically
available on an affordable basis on Ebay or eham.net etc. Well, of course,
expensive is a relative term, for a student hobby organization, it's a lot,
and I guess for small ham operators it is also moderately expensive.
This may be a frequently asked topic: does any one have experienced with
(tested) kit designs for AZ-EL rotors that can be made with parts from
current suppliers ? I know there are a number of controller designs, but I
am interested to know if there are any options for suppliers of the
required gears/motors etc.
I have located several large AC motors / DC motors at my university
mechanical engineering workshop, but they are not all guaranteed the same
specs. I now realize if I do embark on a actual design process with my
model/simulation/hardware, it would be nice to build several of these all
at once to share the development cost over the production run, and ensure
those who want a cheap AZ-EL system can get one. Otherwise the production
cost of one heavy duty system is going to be quite high.
I hope some of you may have suggestions for me, both (+) and (-) or perhaps
(~) in nature. I thought amsat / amateur radio folks have a common need to
encourage homebrew activity to keep their brain cells in working condition?
I'm opening this question up to the national US audience, and welcome any
discussion on the challenges of making the ever-so-important
azimuth-elevation rotor. I've studied some of the alternatives: Alliance
U100 and Yaesu G-5500. I think we can do better in 2013. But ideally, to
allow the wide adoption of AMSAT ground stations, what price point would
the system have to be to make it worth building ?
73 de N3RDX
George Washington University
I had a great time at the AMSAT-DC meeting on Saturday. I greatly
appreciated the contributions, ideas, and questions from all the
participants. HUGE THANKS to Pat Kilroy and to NASA GSFC for hosting!
Since I went on quite a bit about cheap antennas, here are some links to
design & construction info and some related information.
Cheap Antennas for the AMSAT LEO's (WA5VJB)
Construction suggestions, tuning, diplexer design. Also discusses
performance of Arrow antenna.
Cheap Yagi for 70 cm (search Amsat.org or internet for the companion 2M
design) - uses foam board!
Controlled Impedance "Cheap" Antennas (WA5VJB)
The original cheap yagi article. Designs for 2M, 220 MHz, 70cm, 902 MHz,
1296 MHz, including AMSAT and FM sections on 70cm. Great ideas for
terrestrial as well as satellite ground station antennas.
The 6 element 2M antenna I had with me on Saturday is VJB's 2M design and
I've used it with reasonable success on 2M terrestrial (tropo, E-skip) and
meteor bounce (FSK441 using WJST software). It's probably about as large
as I'd want to use for a VHF rover station or portable installation. It's
larger than necessary for use with LEO satellites; a much lighter boom & 3
or 4 elements are more than sufficient. There have been several published
handheld designs that are 2 elements, and the Arrow (even with alleged
performance issues) is a 3 element design.
WA5VJB Herringbone Log-Periodic for satellites:
Interesting design, simple, very portable (designed for hand-held).
DK7ZB's designs. http://www.qsl.net/dk7zb/start1.htm
Huge wealth of information here! Probably better performance than the
WA5VJB designs, but more demanding of precise construction. Most of his
designs are in metric units but some have English measurements as well.
There are several standard inch dimension rods that are close enough to
metric sizes to work. And you can get metric-dimensioned components ,
too. Many examples of ingenious construction techniques in the photos.
His area of interest in terrestrial weak-signal communications; many of his
designs are VERY optimized for 144.2 MHz and 432.2 MHz, particularly the
lower impedance designs. So stick with the smaller 50 ohm designs for
The 2M/70cm-Yagis Ultralight page is probably most useful for satellite
antennas. http://www.qsl.net/dk7zb/PVC-Yagis/PVC-details.htm Many of the
designs are available from SOTABeams (UK) http://www.sotabeams.co.uk and as
kits from Attila Kocis DL1NUX, Nuxcom, http://www.nuxcom.de. Some
satellite-specific ideas & info:
Using electric fence post insulators as element mounts (especially for
DK7ZB and WA5VJB both assume the antenna elements are insulated from the
boom. If you use an aluminum boom (recycled antenna pieces, ¾"x ¾"
extrusions from Lowes/Home Depot), you have to mount the elements above the
boom or with insulated plugs through the boom (and worry about boom
correction factors). These insulators are a good alternative. And I don't
understand why the Europeans get all the cool design small parts. Less
exotic looking ones are available on Ebay & Amazon (and probably at
farm/horse supply stores, Tractor Supply, etc.). I purchased a big bag of
them off Ebay and plan to experiment with this approach.
Antenna element materials: WA5VJB recommends welding rod (cheap, elements
may require splicing with hobby tubing to get lengths for 2M), #10 solid
copper wire ($$), solid aluminum guy wire (old versions - Radio Shack
discontinued the product several years ago), hobby tubing/rods (can get
$$). Several online vendors sell a variety of aluminum rod and brass rod,
some will cut to custom length at small additional cost if you are as inept
as I am with hand tools! Watch shipping charges if you go over 48" in
length. On the 6 element 2M antenna I displayed, I spliced the 2M driven
element for that reason. The local big box stores generally don't stock
small enough diameters/long enough lengths but it's worth a look. Or hit
Timonium or Manassas and see what's in the flea market.
http://ww.speedymetals.comhttp://www.onlinemetals.com (I think I ordered from them)
http://www.mcmaster.com/#standard-aluminum-rods/=m17g2q [Thank you to
Sambudra for reminding me of M-C] McMaster-Carr sells the rod stock in 6ft
lengths; I haven't checked if they have oversize shipping charges. They
sell a lot more than just metals.
The above designs can make circularly polarized antennas. The 2nd set of
elements is mounted at 90 degrees on the boom and is offset by ¼ wavelength
(free space, I believe). It's fed in parallel with the 1st set. Since
both antennas are 50 ohm designs, there are at least 2 solutions to deal
with the parallel impedance:
1. Make a matching harness from coax of carefully cut and assembled
2. Purchase or build a power divider (both Directive Systems and M2
Antennas sell them), use IDENTICAL lengths of 50 ohm feedline to the
Note - According to the Directive Systems website, the company has been
sold and is in the process of moving to HAYMARKET VIRGINIA this week!
RF Connection (therfc.com) in Gaithersubrg MD is an excellent local source
of feedline, connectors, couplers, and associated parts. He can also make
custom harnesses (those phasing lines). Attends all the local hamfests, so
good way to save on shipping large amounts of coax across the country.
I did not discuss omnidirectional antennas. The quadrafiller helix and
Lindenblad were mentioned at the meeting, and Pat had a Lindenblad on
display. These antennas have a reputation as difficult to build. A
passive Lidenblad design was published in QST (or maybe AMSAT journal) a
few years ago and looks much easier to build. No idea how well they
actually perform. The local RF noise level is high enough that higher-gain
antennas may be a requirement around the DC area.
WB4APR has recommended for years using a low-moderate gain yagi elevated 15
degrees (some folks go for 20). Rotate in azimuth and don't worry about
elevation - most passes are not close to overhead and the satellite spends
very little time there. And when it is close, the shorter range and path
loss make up for the loss in antenna gain (at least for smaller antennas -
a very tight EME array is a different matter!)
Preamps - besides the wideband RX-only model AMSAT sells, there are several
sources mentioned on Saturday. Advanced Receiver Research's product list
is here http://www.advancedreceiver.com/page2.html
Hope this is of use to folks and look forward to the next meeting & meeting
you on the air locally, and on the birds!
FM18 Herndon, VA
Steve Greene ks1g04(a)gmail.com <kay ess one gee zero four>@gmail.com
I HAD A RADICAL IDEA for a fellow AMSAT
member who reads this message, to make it
his or her own, and run with it. . . .
WHAT IF we have a *great* turn out for our
Spring Workshop and are "burdened" with
either too many hardware setups overflowing
the VC auditorium or too many non-hardware-
toting attendees (i.e., lots and lots of
non-AMSAT members)? . . .
WHAT IF someone runs a Sat Pass List for our
location for all amateur and Wx satellites
on our workshop date? . . .
WHAT IF the weather on Saturday morning,
March 23, turns out to be an outrageously
beautiful day? . . .
THEN, wouldn't it be awesome if one of us
were to set up a "fully functioning" (you
define) portable satellite ground station
outdoors immediately outside the VC audi-
torium to actively attempt receptions, and
perhaps some two-way contacts as well?!!
THINK of the possibilities!
THINK of the potential benefits!
That extra touch would certainly be "News
at 11" material.
Pat Kilroy, N8PK
P.S. If you haven't noticed yet, the exact
location in mind is shown in two of the
photos displayed on the AMSAT-DC workshop
Dear fellow AMSAT members,
Please go to http://patkilroy.com/amsat-dc/
and read everything top to bottom.
Then please let me know if you have any
comments, questions, recommended edits or
anything else before I send it off to be
published in this weekend's ANS bulletins.
This is our workshop. Only a couple weekends
away. I hope you can attend.
1. We are looking for someone to bring a UHF
signal source for test purposes for the day,
something more substantial than an FM handheld
transceiver if possible. A simple analog SSB
transmitter in very low power mode looping a
recorded voice message would work, and be pretty
cool too. Takers, any one? Please contact me.
2. BRING YOUR CAMERA. Free WiFi.
3. We still need volunteers for this event. The
task list is quite similar to those of our previous
seminars and workshops (see Archives). This event
is run by volunteers for volunteers. For example,
two AMSAT greeters are needed. Also, a video person
with lights, a video editor person, a food organizer,
a Net Control Station for talk-in, go-fers, clean up
crew for examples. (I believe Art Feller is going to
bring his nice big dSLR still camera and gear, so we
are covered for publish-ready type still photos.)
4. We need to get the word out. Can you pass the
word and the amsat-dc Web page URL to your club news-
letter or on a Net? Talk it up on your repeater?
Tell a college kid? (YES!)
Who knows how to get an event announced on Newsline?
On the MDC section Web page and newsletter? Please do!
5. Have you registered through Martha yet? (Please
call her even if you only "might" make it: Unlike
local hamfests where you can walk right in, THERE
WILL BE NO registration on the day of the event!)
THANK YOU for your support.
We will have a great time!