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Comm Ant. Top or Bottom?



 
 
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  #1  
Old January 21st 09, 06:34 PM posted to rec.aviation.homebuilt
Gig 601Xl Builder
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Posts: 683
Default 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.
  #2  
Old January 21st 09, 06:50 PM posted to rec.aviation.homebuilt
[email protected]
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Posts: 472
Default Comm Ant. Top or Bottom?

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
  #3  
Old January 21st 09, 11:40 PM posted to rec.aviation.homebuilt
stol
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Posts: 161
Default Comm Ant. Top or Bottom?

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.
  #4  
Old January 22nd 09, 12:28 AM posted to rec.aviation.homebuilt
Ron Wanttaja
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Posts: 756
Default Comm Ant. Top or Bottom?

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
  #5  
Old January 22nd 09, 01:01 AM posted to rec.aviation.homebuilt
Stuart Fields
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Posts: 43
Default Comm Ant. Top or Bottom?


"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.


  #6  
Old January 22nd 09, 01:12 AM posted to rec.aviation.homebuilt
Wayne Paul
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Posts: 905
Default Comm Ant. Top or Bottom?

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.




  #7  
Old January 22nd 09, 04:03 AM posted to rec.aviation.homebuilt
Stuart Fields
external usenet poster
 
Posts: 43
Default Comm Ant. Top or Bottom?


"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


  #8  
Old January 22nd 09, 07:51 AM posted to rec.aviation.homebuilt
Wayne Paul
external usenet poster
 
Posts: 905
Default Comm Ant. Top or Bottom?


"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


  #10  
Old January 22nd 09, 05:41 PM posted to rec.aviation.homebuilt
RST Engineering
external usenet poster
 
Posts: 1,147
Default Comm Ant. Top or Bottom?


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


 




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