"professorpaul" wrote in message
...
On Aug 7, 5:03 pm, Cecil Moore wrote:
Helmut Wabnig wrote:
The LPDA is "self-adjusting" and easy to make.
And you may change frequency any time.

Question is: Why would an amateur radio operator
want to cover 148 MHz to 420 MHz with a transmitting
antenna?
--
73, Cecil, IEEE, OOTC, http://www.w5dxp.com

I only want to cover 144 and 420, nothing in between! Just for LEO
satellites, where the uplink is on 144 and the downlink is 420, or vis
versa.

/paul W3FIS

I have an ELK and it works on those frequencies out of the box without any
tuning. The 5 element ELK has the same performance as Cushcraft 2/70 beam
it replaced. The Cushcraft was essentially two separate 3 element Yagis (6
elements) with a splitter harness to feed the two.

You say you only want to work 2 specific frequencies, but for the Yagi you
will have to make adjustments because most that are pre-tuned, are optimized
for 146-148 on 2 meters. Also, very few hams are content to stay on one
frequency. There is so much to do and experiment with. ELK actually
performs as a beam from 144 Mhz multi-mode action to far flung NOAA WX
stations at 162 Mhz. ELK works at both ends of 2 meters without tuning.

It is also lightweight, portable and takedown and assembly is quick and
easy. The downside is that you need to use lockwashers on the elements and
glue the tips or they will work loose in the wind. Mine has been up for 5
years and I added a bell crank/pulley and cord running to the base of the
mast to change polarization.

The upper limit of gain for a Log-Periodic is about 10db. A 3 element Yagi
is about 7db and a 5 element is about 9 db. You have to go to a long boom
to exceed 10 db with a Yagi.

There have been several LPDA construction articles in QST over the years,
and there are a few on the Internet too. One that looked interesting, used
angle stock bolted together with Nylon hardware for the boom/feeder, and
another that used parallel Copper tubes with the coax routed from the rear
through one of the tubes for the front feed point. One real big plus is
that you can get Brass and Aluminum tubing and rod in numerous hobby shops
and hardware stores stock sizes that are just too short for 1/2 wave on 2
meters.

Jim Lux wrote:
On Aug 6, 7:06 pm, professorpaul wrote:
Does anyone have design for a log periodic antenna comparable to the
Elk one for 2 meters and 70 cm. I'd like to build one for satellite
work, and with the log periodic, I believe I could avoid the diplexer
issue.

Please respond directly to

Thanks!
/paul W3FIS

Actually, for a dual band to one feed, you can probably just
interleave the elements of a 2m and 70cm beam on the same boom and
connect the driven elements in parallel.

http://www.arrowantennas.com/ look at the model 146/437... they have
plans on the site to build it yourself. While they have a filter box
available, I'm not sure you actually need it.

Except most of these designs don't work well. The problem is that the
2m elements really mess up what you're trying to do on 70.

There are ways to deal with it. One is that you tilt the elements
forward and use them for both bands. Old trick.

tom
K0TAR