Comm Ant. Top or Bottom?

It's time to mount my comm antenna and I am getting mixed reviews which
is better top or bottom. Since I doubt I'll be doing any rough field
landings that isn't an issue. I'm sort of leaning to it just doesn't matter.

In electrical terms it doesn't really matter, assuming the locations
offer a ground-plane that is more or less identical. But the fact
your airplane did not come with an antenna array already installed
begs the question as to type, age, method of construction and so
forth.

For maintenance however, antennae mounted to the top of the structure
usually offer some benefits. But as always, this is a general rule;
you will run into exceptions... without which this Group could not
survive! :-)

Just be careful not to measure Field Strength readings for a system
using the lower side of the hull, since the proximity of the earth
will skew your readings. Your 'Free Space' radiation pattern should
be identical, top or bottom. But here again, that 'Free Space' only
appears in text books. Ain't nothing 'free' nowadays :-)

-R.S.Hoover

On Jan 21, 10:34*am, Gig 601Xl Builder
wrote:
It's time to mount my comm antenna and I am getting mixed reviews which
is better top or bottom. Since I doubt I'll be doing any rough field
landings that isn't an issue. I'm sort of leaning to it just doesn't matter.

On my 801 with a Icom- 200 I mounted it on the bottom. You spend 99%
of the time flying and the radios you are transmitting to are on the
face of the earth, ie, under you, so the bottom seems logical.. Mine
works great down there. YMMV.

Ben.

stol wrote:
On Jan 21, 10:34 am, Gig 601Xl Builder
wrote:
It's time to mount my comm antenna and I am getting mixed reviews which
is better top or bottom. Since I doubt I'll be doing any rough field
landings that isn't an issue. I'm sort of leaning to it just doesn't matter.

On my 801 with a Icom- 200 I mounted it on the bottom. You spend 99%
of the time flying and the radios you are transmitting to are on the
face of the earth, ie, under you, so the bottom seems logical.. Mine
works great down there. YMMV.

Mine is mounted *inside*. :-)

http://www.bowersflybaby.com/stories/antenna.htm

Ron Wanttaja

"Ron Wanttaja" wrote in message
...
stol wrote:
On Jan 21, 10:34 am, Gig 601Xl Builder
wrote:
It's time to mount my comm antenna and I am getting mixed reviews which
is better top or bottom. Since I doubt I'll be doing any rough field
landings that isn't an issue. I'm sort of leaning to it just doesn't
matter.

On my 801 with a Icom- 200 I mounted it on the bottom. You spend 99%
of the time flying and the radios you are transmitting to are on the
face of the earth, ie, under you, so the bottom seems logical.. Mine
works great down there. YMMV.

Mine is mounted *inside*. :-)

http://www.bowersflybaby.com/stories/antenna.htm

Ron Wanttaja

I had a bent Com antenna on the bottom of my Baby Belle helicopter. A
survey of its characteristics, looking from the coax fitting that connects
to the Microaire, showed a minimum VSWR of 3 accross the band. This ain't
good. I lost 25% of my range with this. I bought a straight antenna and
couldn't mount it on the bottom due to clearance and Voila VSWR accross the
band was less than 2. Beware of the bent antennas. Antenna mfr says VSWR 3
is normal.

Mine is a bent 1/4 wave length antenna mounted on the top of the metal tail
cone. My radio is a 1 watt Filser ART 57. So far I haven't had a problem
communicating airborne aircraft or ground stations.
http://www.soaridaho.com/Schreder/HP...P-14_N990d.jpg
http://www.soaridaho.com/Schreder/HP...0_Borah_Mt.jpg
http://www.soaridaho.com/Schreder/HP.../N990_rain.jpg

Wayne
HP-14 "6F"
http://www.soaridaho.com/



"Stuart Fields" wrote in message
...

"Ron Wanttaja" wrote in message
...
stol wrote:
On Jan 21, 10:34 am, Gig 601Xl Builder
wrote:
It's time to mount my comm antenna and I am getting mixed reviews which
is better top or bottom. Since I doubt I'll be doing any rough field
landings that isn't an issue. I'm sort of leaning to it just doesn't
matter.

On my 801 with a Icom- 200 I mounted it on the bottom. You spend 99%
of the time flying and the radios you are transmitting to are on the
face of the earth, ie, under you, so the bottom seems logical.. Mine
works great down there. YMMV.

Mine is mounted *inside*. :-)

http://www.bowersflybaby.com/stories/antenna.htm

Ron Wanttaja

I had a bent Com antenna on the bottom of my Baby Belle helicopter. A
survey of its characteristics, looking from the coax fitting that connects
to the Microaire, showed a minimum VSWR of 3 accross the band. This ain't
good. I lost 25% of my range with this. I bought a straight antenna and
couldn't mount it on the bottom due to clearance and Voila VSWR accross
the band was less than 2. Beware of the bent antennas. Antenna mfr says
VSWR 3 is normal.

"Wayne Paul" wrote in message
...
Mine is a bent 1/4 wave length antenna mounted on the top of the metal
tail cone. My radio is a 1 watt Filser ART 57. So far I haven't had a
problem communicating airborne aircraft or ground stations.
http://www.soaridaho.com/Schreder/HP...P-14_N990d.jpg
http://www.soaridaho.com/Schreder/HP...0_Borah_Mt.jpg
http://www.soaridaho.com/Schreder/HP.../N990_rain.jpg

Wayne
HP-14 "6F"
http://www.soaridaho.com/



"Stuart Fields" wrote in message
...

"Ron Wanttaja" wrote in message
...
stol wrote:
On Jan 21, 10:34 am, Gig 601Xl Builder
wrote:
It's time to mount my comm antenna and I am getting mixed reviews
which
is better top or bottom. Since I doubt I'll be doing any rough field
landings that isn't an issue. I'm sort of leaning to it just doesn't
matter.

On my 801 with a Icom- 200 I mounted it on the bottom. You spend 99%
of the time flying and the radios you are transmitting to are on the
face of the earth, ie, under you, so the bottom seems logical.. Mine
works great down there. YMMV.

Mine is mounted *inside*. :-)

http://www.bowersflybaby.com/stories/antenna.htm

Ron Wanttaja

I had a bent Com antenna on the bottom of my Baby Belle helicopter. A
survey of its characteristics, looking from the coax fitting that
connects to the Microaire, showed a minimum VSWR of 3 accross the band.
This ain't good. I lost 25% of my range with this. I bought a straight
antenna and couldn't mount it on the bottom due to clearance and Voila
VSWR accross the band was less than 2. Beware of the bent antennas.
Antenna mfr says VSWR 3 is normal.
Wayne: All my experience with antennas says that you are not getting as
much as you can due to the high VSWR. That said, if you are getting
everything that you want, why change? Those photos are great. I can
understand why you fly one of them "quiet things". Still haven't gone for a
sail plane ride but it is certainly in my "round to it" bucket.

stu

"Stuart Fields" wrote in message
...

"Wayne Paul" wrote in message
...
Mine is a bent 1/4 wave length antenna mounted on the top of the metal
tail cone. My radio is a 1 watt Filser ART 57. So far I haven't had a
problem communicating airborne aircraft or ground stations.
http://www.soaridaho.com/Schreder/HP...P-14_N990d.jpg
http://www.soaridaho.com/Schreder/HP...0_Borah_Mt.jpg
http://www.soaridaho.com/Schreder/HP.../N990_rain.jpg

Wayne
HP-14 "6F"
http://www.soaridaho.com/


Wayne: All my experience with antennas says that you are not getting as
much as you can due to the high VSWR. That said, if you are getting
everything that you want, why change? Those photos are great. I can
understand why you fly one of them "quiet things". Still haven't gone for
a sail plane ride but it is certainly in my "round to it" bucket.

stu

Thank you for the complements on the picture. I really enjoy the old HP-14
homebuilt. It was designed in 1964. Mine was completed in 1973 (I
purchased it in 1999.) On Aug 7, 2007 I managed to complete a declared 300
km flight.
http://www.soaridaho.com/Flights/6F_Gold_Distance.html

If you ever have the opportunity to get a flight in a high performance
two-place sailplane ... do it!!

BTW, what makes you think that I have a high SWR? Normally sailplane
communicate with their crews and other sailplanes on 123.3 or 124.5 MHz. I
have tuned my antenna for 123.3 MHz At that frequency the SWR is 1.2 to 1.
At the extremes of the comm frequencies it does not exceed 2 to 1.

Wayne
Amateur Radio W7ADK

wrote:
In electrical terms it doesn't really matter, assuming the locations
offer a ground-plane that is more or less identical. But the fact
your airplane did not come with an antenna array already installed
begs the question as to type, age, method of construction and so
forth.

For maintenance however, antennae mounted to the top of the structure
usually offer some benefits. But as always, this is a general rule;
you will run into exceptions... without which this Group could not
survive! :-)

Just be careful not to measure Field Strength readings for a system
using the lower side of the hull, since the proximity of the earth
will skew your readings. Your 'Free Space' radiation pattern should
be identical, top or bottom. But here again, that 'Free Space' only
appears in text books. Ain't nothing 'free' nowadays :-)

-R.S.Hoover

The antenna in question is a Comant CI122 bent whip. Considering all the
advice I will mount it on the bottom but make sure there is enough
service loop in the cable to move it if it doesn't work out.

BTW, what makes you think that I have a high SWR? Normally sailplane
communicate with their crews and other sailplanes on 123.3 or 124.5 MHz.
I have tuned my antenna for 123.3 MHz At that frequency the SWR is 1.2
to 1. At the extremes of the comm frequencies it does not exceed 2 to 1.


I do not find 124.5 as a legal sailplane frequency in my copy of the FCC
regs. Mind giving me a pointer to it?

BTW, snippety doo-dah, snippety aye is a GOOD thing to do.

Jim