for sat work, wondering what antenna type might be better or if they
are close

i've seen those corkscrew like, helical's and say the M2 beam, with
switchable,& cir/pol



performance wise are they in the ball park, does one have a clear adv
over the other in a particular circumstance??


thanks

i've seen those corkscrew like, helical's and say the M2 beam, with
switchable,& cir/pol



performance wise are they in the ball park, does one have a clear adv
over the other in a particular circumstance??

Check out the last bit of this page:

http://www.cebik.com/vhf/gh3.html

It's got the sort of comparison you're looking for...

In article .com,
" wrote:

i've seen those corkscrew like, helical's and say the M2 beam, with
switchable,& cir/pol



performance wise are they in the ball park, does one have a clear adv
over the other in a particular circumstance??

Check out the last bit of this page:

http://www.cebik.com/vhf/gh3.html

It's got the sort of comparison you're looking for...

wow, this was a great site, thanks very much !!!

i have to ponder now , what the helical ant bigger sidelobs might do
in my area

The main advantage of a helix is that it "gives" you circular
polarization for "free"...you don't have to phase or split anything.
The disadvantage is generally that they're relatively heavy and they do
require something of a reflector screen behind them, although there are
variants that use a ring reflector similar to what you'd see in a quad
antenna.

Helices have excellent impedance bandwidth, but really the point of
Cebik's article is that the pattern bandwidth is not nearly as large as
the impedance bandwidth. So really it's best to think of them as
single-band antennas like a yagi.

As to sidelobes specifically, you don't really care about that on
transmit for satellite work. But they are important (and to be
avoided) in receive and especially at microwave frequencies. As an
example, in the initial stages of AO-40 (2.4GHz earth receive) many
started with long (5') helices, but quickly realized that small TVRO
dishes were quite superior even though the gain of the two antennas was
about the same.

One great advantage that phased yagis have is that you can switch the
sense of circular polarization--very hard to do that with a helix.
Sometimes satellite links can be improved by switching either your
transmit or receive sense, depending on the relative satellite
orientation and motion.


ml wrote:
for sat work, wondering what antenna type might be better or if they
are close

i've seen those corkscrew like, helical's and say the M2 beam, with
switchable,& cir/pol performance wise are they in the ball park, does one have a clear adv
over the other in a particular circumstance??


thanks

In article .com,
"nx7u" wrote:

The main advantage of a helix is that it "gives" you circular
polarization for "free"...you don't have to phase or split anything.
The disadvantage is generally that they're relatively heavy and they do
require something of a reflector screen behind them, although there are
variants that use a ring reflector similar to what you'd see in a quad
antenna.

Helices have excellent impedance bandwidth, but really the point of
Cebik's article is that the pattern bandwidth is not nearly as large as
the impedance bandwidth. So really it's best to think of them as
single-band antennas like a yagi.

As to sidelobes specifically, you don't really care about that on
transmit for satellite work. But they are important (and to be
avoided) in receive and especially at microwave frequencies. As an
example, in the initial stages of AO-40 (2.4GHz earth receive) many
started with long (5') helices, but quickly realized that small TVRO
dishes were quite superior even though the gain of the two antennas was
about the same.

One great advantage that phased yagis have is that you can switch the
sense of circular polarization--very hard to do that with a helix.
Sometimes satellite links can be improved by switching either your
transmit or receive sense, depending on the relative satellite
orientation and motion.


ml wrote:
for sat work, wondering what antenna type might be better or if they
are close

i've seen those corkscrew like, helical's and say the M2 beam, with
switchable,& cir/pol performance wise are they in the ball park, does one
have a clear adv
over the other in a particular circumstance??


thanks

this did help me interpert the article a bit more, i was on track at
least really appreciate both of your help!!

for 2m most of the antennas i've looked at such as the m2 it seems i
am liking best, is a bit too long and was hoping to find a simular
but shorter antenna as it's a typical beam perhaps i can just chop
a bit off the ends' the helical's i've seen were all a bit
physically boom wise shorter but i guess not worth it performance wise

When I was in the Air Force our helical SATCOM antenna got trashed. We put
together a pair of Yagis made of 2x2s and solid ground wire and a phasing
harness. When we first put it together we thought we had really messed up
but then we reversed the connexctions on the harness we were able to get a
solid signal. later the antenna was improved on and the crossed Yagis became
our antenna of choice. New and improved version was made with aluminum rods
and a fiberglass boom and the driven element became a folded dipole with a
hairpin match. We were in the middle of an operational readiness inspection
and the SATCOM guys got special recongnition for adapting to the situation.
The antenna does have its limitations comared to the helix. The helix is
significantly more broadbanded.