[amsat-dc] Thank you & antenna links

Stephan Greene ks1g04 at gmail.com
Mon Mar 25 14:52:01 PDT 2013


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
satellite use.

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
aluminum booms)
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.

Internet Vendors:
http://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
antenna feedpoints.

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!

Steve, KS1G
FM18 Herndon, VA

Steve Greene  ks1g04 at gmail.com  <kay ess one gee zero four>@gmail.com

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