Log periodic antenna
professorpaul
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 W3...@arrl.net
Thanks!
/paul W3FIS
Jim Lux
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.
Jerry
"professorpaul" <dead...@comcast.net> wrote in message
news:573444b6-9301-4c0b...@33g2000vbe.googlegroups.com...
Hi Paul
"For what it is worth", I support Jim Lux's advice. A 70 cm Yagii wont
couple much power from the transmitter when sending on 2.meters It would
be easy to test the effect of shunting the 435 receiving Yagii with the 2
meter Yagii. You could even do that with EZNEC.
An antenna like Jim suggests would be easy to build on a broom stick to
test the effects of the 'other antenna'.
The principal value of the Log Periodic is it's bandwidth. That is not
significant when only two discrete frequencies are considered. A
disadvantage of the Log Periodic is it's limited gain. I fail to see where
the Log Periodic benefits the user when only two frequencies are being
considered.
Jerry KD6JDJ
Helmut Wabnig
wrote:
Mechanical and electrical precision.
A single frequency antenna must be tuned very carefully.
The LPDA is "self-adjusting" and easy to make.
And you may change frequency any time.
w.
Cecil Moore
> 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
Jerry
"Helmut Wabnig" <hwabnig@ .- --- -. dotat> wrote in message
news:k9to75ttf18fgvsl6...@4ax.com...
Hi W
I hadnt realized that Yagiis were so difficult to build and tune. Have
you considered telling the AMSAT guys about how they can benefit from your
advice? It seems that most of the AMSAT guys have been using the "Arrows"
for LEO satellite work.
Jerry KD6JDJ
professorpaul
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
Jerry
/paul W3FIS
Hi Paul
AO-51 is a good HAM satellite. It is 146 up and 435 down.
If you do want to get some good experience designing Log Periodic
antennas, you might consider a Log Periodic V. The V configuration takes
advantage of a three to one frequency spread, where a center fed 1/2 wave
dipole becomes 3/4 wave at 3 times the frequency. The low frequencie
pattern is little effected by the "V". The high frequencies (3 times the
low frequencies) appreciate the bending to the V because that allows the
sidelobes to add toward the "front".
Jerry KD6JDJ
Dave
>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.
then forget all the complications of log periodics and just make 2 simple
yagis on the same boom. that is the common method of constructing
directional satellite antennas. same boom too complicated, just make 2
separate ones and mount them on a cross arm a few feet apart.
Cecil Moore
> On Aug 7, 5:03 pm, Cecil Moore <nos...@w5dxp.com> wrote:
>> Question is: Why would an amateur radio operator
>> want to cover 148 MHz to 420 MHz with a transmitting
>> antenna?
>
> satellites, where the uplink is on 144 and the downlink is 420, or vis
> versa.
Then you would be wasting 98% of the frequency coverage
of the log periodic. The unused antenna elements would
constitute almost the total cost of the antenna.
JB
/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.
tom
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