February 19th 09, 06:50 PM
It's antenna-decision-time for my Europa kitplane; though I purchased
a couple of Bob Archer antennae w/ my kit, my sparse knowledge on the
subject (make that next to zero), has led me to reconsider the issue
as a blank slate. I'm thinking I'll be needing antennae for 2 coms, 1
nav, transponder, and ELT. Not interested in wasting dollars, but
usually willing to pop for something which assures trouble-free
operations, particularly when I'll be having wing tip and tail mounted
strobes (3) which I gather can sometimes complicate things.
My research led me to RST's website...I've always enjoyed Jim Weir's
articles, and years ago built one of his intercoms which served me
well. His $29 antenna package w/ textbook for plastic airplanes
sounded great.
As I investigated further, I received this email from a pal who knows
his avionics:
Asking his opinion on RST's offerings, I wrote, "For $29, Jim can
solve all the antenna issues for a plastic airplane...now, I know, I
know...something too good to be true probably isn't...but...every now
and then. Your thoughts?"
And my pal responded:
"You can make dipoles fairly easily, but they will have to be tuned
for the specific frequencies that they will be used for. preferably
once they are installed in the airplane. You will also need a "balun"
to balance the impedance of the elements to the impedance of the feed
line. It isn't as complicated as it sounds, but most folks don't have
the gear to tune home made antennas and wind up relying on someone
with a ham license who has the gear, or taking it to a radio shop.
This is especially true of the transponder antenna, as you will be
hard pressed to find a ham operator who has the capability to tune an
antenna at 1090 Mhz. The COM frequency band (118-136 Mhz) is a bit
more common to hams, though. Most 2 meter test gear will handle those
frequencies.
"FWIW, I have both the sweep test gear (I can sweep anything from 30
Mhz to 32 Ghz with my sweep gear) and the knowledge of how to make my
antennas, but I chose to use the AAE antennas because I liked the
material they were made from and it was one less thing I had to do to
get my bird into the air. It would have been difficult for me to
reproduce what AAE does for their price in terms of quality and
performance. There's nothing wrong with a copper tape antenna, though,
provided you tune the antenna to minimize the SWR (reflected power)
across the band."
Now my only "sweeping" equipment and experience is on the end of a
broom...and I live on an island without a convenient neighborhood
radio shop, and the only ham I'm familiar with comes in a sandwich.
So my questions for this discussion (and for Jim, if he's monitoring
this) are, taaa daaa,
1. What's involved in "tuning" an antenna? (Can proper tuning be
assured by careful measurement and installation...or must one have
both access to the antenna for trimming, and diagnostic equipment of
some kind?)
2.What's involved in "sweeping" an antenna? What equipment is needed,
and what is the nature of any alterations to the antenna which the
process of sweeping reveals?
3. Can these issues of tuning and sweeping be ignored by buying off-
the-shelf products?
Humbly,
Fred
a couple of Bob Archer antennae w/ my kit, my sparse knowledge on the
subject (make that next to zero), has led me to reconsider the issue
as a blank slate. I'm thinking I'll be needing antennae for 2 coms, 1
nav, transponder, and ELT. Not interested in wasting dollars, but
usually willing to pop for something which assures trouble-free
operations, particularly when I'll be having wing tip and tail mounted
strobes (3) which I gather can sometimes complicate things.
My research led me to RST's website...I've always enjoyed Jim Weir's
articles, and years ago built one of his intercoms which served me
well. His $29 antenna package w/ textbook for plastic airplanes
sounded great.
As I investigated further, I received this email from a pal who knows
his avionics:
Asking his opinion on RST's offerings, I wrote, "For $29, Jim can
solve all the antenna issues for a plastic airplane...now, I know, I
know...something too good to be true probably isn't...but...every now
and then. Your thoughts?"
And my pal responded:
"You can make dipoles fairly easily, but they will have to be tuned
for the specific frequencies that they will be used for. preferably
once they are installed in the airplane. You will also need a "balun"
to balance the impedance of the elements to the impedance of the feed
line. It isn't as complicated as it sounds, but most folks don't have
the gear to tune home made antennas and wind up relying on someone
with a ham license who has the gear, or taking it to a radio shop.
This is especially true of the transponder antenna, as you will be
hard pressed to find a ham operator who has the capability to tune an
antenna at 1090 Mhz. The COM frequency band (118-136 Mhz) is a bit
more common to hams, though. Most 2 meter test gear will handle those
frequencies.
"FWIW, I have both the sweep test gear (I can sweep anything from 30
Mhz to 32 Ghz with my sweep gear) and the knowledge of how to make my
antennas, but I chose to use the AAE antennas because I liked the
material they were made from and it was one less thing I had to do to
get my bird into the air. It would have been difficult for me to
reproduce what AAE does for their price in terms of quality and
performance. There's nothing wrong with a copper tape antenna, though,
provided you tune the antenna to minimize the SWR (reflected power)
across the band."
Now my only "sweeping" equipment and experience is on the end of a
broom...and I live on an island without a convenient neighborhood
radio shop, and the only ham I'm familiar with comes in a sandwich.
So my questions for this discussion (and for Jim, if he's monitoring
this) are, taaa daaa,
1. What's involved in "tuning" an antenna? (Can proper tuning be
assured by careful measurement and installation...or must one have
both access to the antenna for trimming, and diagnostic equipment of
some kind?)
2.What's involved in "sweeping" an antenna? What equipment is needed,
and what is the nature of any alterations to the antenna which the
process of sweeping reveals?
3. Can these issues of tuning and sweeping be ignored by buying off-
the-shelf products?
Humbly,
Fred