On Wed, 15 Apr 2015 13:56:53 -0700, (Dave
Platt) wrote:

I recently lucked into a bin-full of Kenwood TK-981 mobile radios

Congrats. That's one of the better and easier to deal with 900 MHz
radios. Watch out for V1 versus V2. They're slightly different:
http://www.kw902.com/981generalinfo.html

Incidentally, what's with the 33 cm wavelength notation? I'll start
using wavelength instead of frequency when HP, TEK, or some other
reputable vendor supplies a frequency counter or generator calibrated
in wavelength instead of the usual frequency or period.

The likely use for these would mostly be as part of an emergency-
response kit, for helping set up command-net and message-net
structures during an exercise, drill, or an actual event.

OK, portable operation. That means mounted on top of a fiberglass
extension pole or floppy PVC pipe.

Due to the
scarcity of 33 cm radios I would not expect that many (if any) of the
individual ARES/RACES operators in our area would be taking part.

Actually, the problem is tremendous spread spectrum noise in parts of
the band. It's common for repeaters to have different output
frequencies, but sharing the few available input frequencies (usually
902.0125 in Northern Calif) that are out of the cordless phone noisy
areas. Of course, they all use different PL tones. See the list of
frequencies at:
http://users.innercite.com/kj6ko/page8.html
and notice the input frequencies. Also:
http://www.repeater-builder.com/tech-info/900mhz-frequencies-to-avoid.html


So... now I need to buy or make antennas for them. I'm interested in
ideas and suggestions.

I've seen a number of DIY designs on the net:

- Simple ground-plane antennas using an N connector and a few wires
soldered on are easy to make, and quite predictable. Unfortunately
the wires sticking out in several directions makes them not all
that "go-kit-friendly". I could figure out a design using (e.g.)
banana plugs and jacks to connect the elements, so the antenna
could be easily "unplugged and knocked down" for storage, but that
seems like a lot of fiddling.

- Several people have published designs for 33 cm J-poles, often with
a collinear structure for higher gain. Fairly predictable but
need some tuning during construction. Go-kit-friendly if installed
in a fiberglass or PVC radome tube.

- Simple sleeve dipoles (fold back the coax braid, trim for SWR,
heat-shrink) are easy, cheap, go-kit-friendly, and should be fairly
robust.

Yagis would also be useful but aren't as go-kit-friendly due to their
size; Kent Britain's "cheap Yagi" design is easy and the ones I've
made for other bands have worked well.

So, any other suggestions for simple-yet-effective DIY antennas for
this band? Are there commercial antennas good and cheap enough that I
should just buy a bunch? Good mobile antennas?




--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558