Today's Message Index:
----------------------
1. 06:03 AM - Re: Re: Antennas general (Robert L. Nuckolls, III)
2. 06:34 AM - Re: Re: Antennas general (sportav8r@aol.com)
3. 06:52 AM - Re: Re: Antennas general (Hopperdhh@aol.com)
4. 08:39 AM - Re: VHF antenna mounting (more hair splitting) ()
5. 09:37 AM - Re: Antennas general (Robert L. Nuckolls, III)
6. 09:49 AM - Antenna Coax Routing (Todd Richmond)
7. 11:09 AM - Re: Antenna Coax Routing (Hinde, Frank George (Corvallis))
8. 12:25 PM - Re: Re: Antennas general (sportav8r@aol.com)
9. 12:25 PM - Re: Re: Antennas general (sportav8r@aol.com)
10. 04:42 PM - Re: Re: Antennas general (Dale Ensing)
11. 06:35 PM - Re: Re: Antennas general (sportav8r@aol.com)
12. 07:18 PM - Off line for a few days (Robert L. Nuckolls, III)
Message 1
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Subject: | Re: Antennas general |
--> AeroElectric-List message posted by: "Robert L. Nuckolls, III" <nuckollsr@cox.net>
At 04:58 PM 7/26/2006 -0700, you wrote:
>--> AeroElectric-List message posted by: "europa flugzeug fabrik"
><n3eu@comcast.net>
>
>
>brian wrote:
> > A 50W transmitter shooting its signal at you using a directional
> antenna when you are less than 2000' away does not require much from the
> receiver and its antenna.
>
>I believe theyre as little as 2.5W, though as highly directional, the
>moral equivalent of higher power relative to like a COM. Perhaps you are
>referring to that.
>
>Also, the sensitivity of the receiver isnt good, maybe 200 times less
>sensitive than a COM. So, the antenna has to be reasonably good. I
>wonder if we could use wire or copper tape to fake an equivalent of a sled
>antenna. One end to shield, center wire about 10 down or wherever, but
>we need a ramp tester to tune it. Or rig it up in the car, and find a
>marker shed we can drive up close to. A coax monopole w/o ground plane as
>proposed will probably be OK.
>
>Fred F.
Lets put some rough orders of magnitude numbers to
this discussion. Assuming 2.5 W transmitter driving
a corner reflector (lets assume 3db gain) for an
ERP of 5 watts, let's plug into:
http://www.megalithia.com/elect/fieldstr.html
With an ERP of .005 Kw and distance of .2 KM.
Leave the channel defaulted at CH44.
This calculator is for UHF frequencies the the
performance at 75 MHz would be only slightly different
due to tiny differences in path losses.
The calculator says we can expect a field strength
on the order of 80 dBuV at .2 Km above this marker
site.
Go to:
http://www.radioing.com/eengineer/rfcalc.html
and enter 80 (dBuV) before punching the box in the lower
right column for DbUv -> Volts conversion and we get:
0.01 volts, or 10,000 microvolts.
Marker beacon receiver sensitivity is on the order of
1500 uV in the LO SENS position and 200 uV in the
HI SENS position. So barring errors in data or logic
it seems that there's a LOT of head-roon for loss of
antenna efficiency.
I've had a number of builders in glass/epoxy airplanes
simply lay a 40" piece of wire out in the tailcone
and run a coax to the marker receiver report excellent
results.
But the bottom line is that what ever one installs that
departs from the installation instructions (hence departures
from the manufacturer's expectations) the installation should
be flight checked by overflying a marker beacon facility
at various altitudes. Returning to
http://www.megalithia.com/elect/fieldstr.html
Enter 1.5 KM into the distance box (5x higher than anything
we would expect to do in a real approach) and we get
62 dBuV field strength. Which converts to a potential
signal level of 1200 uV to a receiver in an IDEAL installation.
Hmmmm . . . one would probably not expect even the best of
installations to function at 5,000 AGL in LO sensitivity but
it should come back alive when you select the HI sensitivity.
A little bit of flight testing is all it takes to see how much
headroom your installation possesses. Data-in-hand trumps
un-quantified supposition every time. The above exercise suggests
that considerable degradation of gross antenna performance is
tolerable and worthy of further exploration.
Bob . . .
Message 2
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Subject: | Re: Antennas general |
While we're discussing dB's, I note that the installation instructions for m
y Garmin GMA 340 audio panel mention several times a feature provinding "10
times gain (20 dB)" for the entertainment channel input. I have labored all
my life under the impression that 10dB was 10x gain, and 20 dB was 100x gai
n. It seems unlikely that the people who design this stuff professionally k
now more about decibels and power gain than a radio hobbyist does, so it's s
afe to assume I'm the one who is missing something. What gives?
Sorry to hijack an antenna thread for this, Bob. But I've just got to get t
his straight before I go nuts ;-)
-Bill B
-----Original Message-----
Sent: Thu, 27 Jul 2006 8:52 AM
--> AeroElectric-List message posted by: "Robert L. Nuckolls, III" <nuckolls
r@cox.net>
At 04:58 PM 7/26/2006 -0700, you wrote:
>--> AeroElectric-List message posted by: "europa flugzeug fabrik" ><n3eu@co
mcast.net>
>
>
>brian wrote:
> > A 50W transmitter shooting its signal at you using a directional > anten
na when you are less than 2000' away does not require much from the > receiv
er and its antenna.
>
>I believe they=C3=A2=82=AC=84=A2re as little as 2.5W, though as highl
y directional, the >moral equivalent of higher power relative to like a COM.
Perhaps you are >referring to that.
>
>Also, the sensitivity of the receiver isn=C3=A2=82=AC=84=A2t good, ma
ybe 200 times less >sensitive than a COM. So, the antenna has to be reasonab
ly good. I >wonder if we could use wire or copper tape to fake an equivalent
of a sled >antenna. One end to shield, center wire about 10=C3=A2=82=AC
=C2=9D down or wherever, but >we need a ramp tester to tune it. Or rig it up
in the car, and find a >marker shed we can drive up close to. A coax monopo
le w/o ground plane as >proposed will probably be OK.
>
>Fred F.
Lets put some rough orders of magnitude numbers to
this discussion. Assuming 2.5 W transmitter driving
a corner reflector (lets assume 3db gain) for an
ERP of 5 watts, let's plug into:
http://www.megalithia.com/elect/fieldstr.html
With an ERP of .005 Kw and distance of .2 KM.
Leave the channel defaulted at CH44.
This calculator is for UHF frequencies the the
performance at 75 MHz would be only slightly different
due to tiny differences in path losses.
The calculator says we can expect a field strength
on the order of 80 dBuV at .2 Km above this marker
site.
Go to:
http://www.radioing.com/eengineer/rfcalc.html
and enter 80 (dBuV) before punching the box in the lower
right column for DbUv -> Volts conversion and we get:
0.01 volts, or 10,000 microvolts.
Marker beacon receiver sensitivity is on the order of
1500 uV in the LO SENS position and 200 uV in the
HI SENS position. So barring errors in data or logic
it seems that there's a LOT of head-roon for loss of
antenna efficiency.
I've had a number of builders in glass/epoxy airplanes
simply lay a 40" piece of wire out in the tailcone
and run a coax to the marker receiver report excellent
results.
But the bottom line is that what ever one installs that
departs from the installation instructions (hence departures
from the manufacturer's expectations) the installation should
be flight checked by overflying a marker beacon facility
at various altitudes. Returning to
http://www.megalithia.com/elect/fieldstr.html
Enter 1.5 KM into the distance box (5x higher than anything
we would expect to do in a real approach) and we get
62 dBuV field strength. Which converts to a potential
signal level of 1200 uV to a receiver in an IDEAL installation.
Hmmmm . . . one would probably not expect even the best of
installations to function at 5,000 AGL in LO sensitivity but
it should come back alive when you select the HI sensitivity.
A little bit of flight testing is all it takes to see how much
headroom your installation possesses. Data-in-hand trumps
un-quantified supposition every time. The above exercise suggests
that considerable degradation of gross antenna performance is
tolerable and worthy of further exploration.
Bob . . .
=========================
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=========================
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=========================
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=========================
===========
________________________________________________________________________
Message 3
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Subject: | Re: Antennas general |
In a message dated 7/27/2006 9:39:55 A.M. Eastern Daylight Time,
sportav8r@aol.com writes:
While we're discussing dB's, I note that the installation instructions for
my Garmin GMA 340 audio panel mention several times a feature provinding "10
times gain (20 dB)" for the entertainment channel input. I have labored all
my life under the impression that 10dB was 10x gain, and 20 dB was 100x gain.
It seems unlikely that the people who design this stuff professionally know
more about decibels and power gain than a radio hobbyist does, so it's safe
to assume I'm the one who is missing something. What gives?
Sorry to hijack an antenna thread for this, Bob. But I've just got to get
this straight before I go nuts ;-)
-Bill B
Bill,
You are correct for POWER gain. For VOLTAGE gain Garmin is right.
Db=10 log (P1/P2)
Db log (V1/V2)
Dan Hopper
K9WEK
RV-7A
Message 4
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Subject: | Re: VHF antenna mounting (more hair splitting) |
Rumen:
Excellent point, that is why this list is great, input from everyone
and splitting hairs or not that is a GREAT IDEA. I have just made
note of this and put it into my RV-7 builders instructions. Thanks
Another hair to split, not that anyone on the list would ever do
that, is not to use stainless steel screws? Why? The base of
the antenna is aluminum alloy. Aluminum and SS is far apart
on the galvanic corrosion chart. Boeing uses passivated/cadmium
plated fasteners not stainless steel. I think the engineers at
Boeing and Cessna might have a clue. Dang engineers what
do they know. :-) All those years in school wasted.
Cheers George M., MSME, ATP/CFII-MEI
>From: rd2@evenlink.com
>Bob,
>Speaking of the magic (grounding the base) - looking at the
>Antenna_Installation.gif , I have seen toothed lock washers used
>between the doubler plate and skin.
>
>This was on a Cessna. The doubler plate was not riveted to the
>skin (it came with with the antenna replacement kit). The lock
>washer assured better el contact (grounding). They used externally
>toothed lock washers, as per attached. Maybe a better idea would
>be to use the external-internal toothed type washers (also attached).
>Opinions?
>
>Rumen
---------------------------------
See the all-new, redesigned Yahoo.com. Check it out.
Message 5
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Subject: | Re: Antennas general |
--> AeroElectric-List message posted by: "Robert L. Nuckolls, III" <nuckollsr@cox.net>
At 09:58 AM 7/26/2006 -0700, you wrote:
>--> AeroElectric-List message posted by: "Hinde, Frank George (Corvallis)"
><frank.hinde@hp.com>
>
> On my Vans kit they provided a wingtip NAV antenna which is just a
>strip of copper foil. Do not suggest how one is supposed to ground it to
>the airframe.
>
>I assume one has to ground the coax braid to the wing somehow??
How is the foil installed? Does it begin right at the edge of
the tip fairing such that transition from coax to antenna is
closely located to metallic portions of the wing? If so, ground
the coax shield to the nearest practical wing-metal.
>Also I intend to run my marker beacon antenna (40" lentgh of stripped
>coax) in the bottom of my cowl. Assuming this will work do I need to
>bond that coax to the firewall or similar?
Here's where having access to a piece of test equipment is
a real help! An MFJ-259 antenna analyzer (See:
http://www.mfjenterprises.com/products.php?prodid=MFJ-259B )
would allow you to run say 10" of straight wire, coil 20"
or so around a piece of plastic or wooden dowel, then extend
the remainder out straight for an overall length of 20"
or so. Then use the antenna analyzer to look at the characteristics
of this shortened antenna. You'll find that it resonates lower
than 75 Mhz. Trim the 10" extension beyond the coil to bring
the antenna up to 75 Mhz then glass over what remains.
Bob . . .
Message 6
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Subject: | Antenna Coax Routing |
Folks,
This might be a newbie question but I'm giving it a shot none the less. I
have an RV-7A (or part of one at this point) in which I am planning on
mounting my VOR and marker beacon antennas in the wingtips (one in each
tip). Can I route my antenna coax in the same conduit with the nav,
landing, and strobe lights or should I do a separate run some distance away
to avoid any potential interference. The current set up has one transformer
for the strobes mounted in the fuselage and a shielded wire running to the
wing tips (the strobes ground back at the transformer). The nav, landing
and taxi lights are grounded locally on the wingtips.
My other concern is that at some point I would like to upgrade to a HID
system for the landing/taxi lights which would require a local power
transformer by the light. Has anybody had any experience with interference
caused by these next to an antenna?
Thanks for any input.
Todd R. Richmond
RV-7A
Message 7
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Subject: | Antenna Coax Routing |
Todd Just a thought but....
If you mount a comm in one wingtip, Nav in the other and marker bacon in
the bottom of the cowl you'll have no com attenna sticking out in the
breeze (at least one less if you have more than one com) and you'll
reduce the amount of coazxyou have to run out to the wings.
Frank
________________________________
[mailto:owner-aeroelectric-list-server@matronics.com] On Behalf Of Todd
Richmond
Sent: Thursday, July 27, 2006 9:42 AM
Folks,
This might be a newbie question but I'm giving it a shot none the less.
I have an RV-7A (or part of one at this point) in which I am planning on
mounting my VOR and marker beacon antennas in the wingtips (one in each
tip). Can I route my antenna coax in the same conduit with the nav,
landing, and strobe lights or should I do a separate run some distance
away to avoid any potential interference. The current set up has one
transformer for the strobes mounted in the fuselage and a shielded wire
running to the wing tips (the strobes ground back at the transformer).
The nav, landing and taxi lights are grounded locally on the wingtips.
My other concern is that at some point I would like to upgrade to a HID
system for the landing/taxi lights which would require a local power
transformer by the light. Has anybody had any experience with
interference caused by these next to an antenna?
Thanks for any input.
Todd R. Richmond
RV-7A
Message 8
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Subject: | Re: Antennas general |
Aw, shoot! Make that P=E^2/R. I knew better than that. Hit "send" too quickly.
-Stormy
-----Original Message-----
Sent: Thu, 27 Jul 2006 9:46 AM
In a message dated 7/27/2006 9:39:55 A.M. Eastern Daylight Time, sportav8r@aol.com
writes:
While we're discussing dB's, I note that the installation instructions for my Garmin
GMA 340 audio panel mention several times a feature provinding "10 times
gain (20 dB)" for the entertainment channel input. I have labored all my life
under the impression that 10dB was 10x gain, and 20 dB was 100x gain. It seems
unlikely that the people who design this stuff professionally know more about
decibels and power gain than a radio hobbyist does, so it's safe to assume
I'm the one who is missing something. What gives?
Sorry to hijack an antenna thread for this, Bob. But I've just got to get this
straight before I go nuts ;-)
-Bill B
Bill,
You are correct for POWER gain. For VOLTAGE gain Garmin is right.
Db=10 log (P1/P2)
Db log (V1/V2)
Dan Hopper
K9WEK
RV-7A
________________________________________________________________________
Message 9
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Subject: | Re: Antennas general |
Ah, the old P=E^2*R ploy. I see now. Thanks.
-----Original Message-----
Sent: Thu, 27 Jul 2006 9:46 AM
In a message dated 7/27/2006 9:39:55 A.M. Eastern Daylight Time, sportav8r@aol.com
writes:
While we're discussing dB's, I note that the installation instructions for my Garmin
GMA 340 audio panel mention several times a feature provinding "10 times
gain (20 dB)" for the entertainment channel input. I have labored all my life
under the impression that 10dB was 10x gain, and 20 dB was 100x gain. It seems
unlikely that the people who design this stuff professionally know more about
decibels and power gain than a radio hobbyist does, so it's safe to assume
I'm the one who is missing something. What gives?
Sorry to hijack an antenna thread for this, Bob. But I've just got to get this
straight before I go nuts ;-)
-Bill B
Bill,
You are correct for POWER gain. For VOLTAGE gain Garmin is right.
Db=10 log (P1/P2)
Db log (V1/V2)
Dan Hopper
K9WEK
RV-7A
________________________________________________________________________
Message 10
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Subject: | Re: Antennas general |
Are you sure it is not E=mc2 ;<)
Aw, shoot! Make that P=E^2/R. I knew better than that. Hit "send"
too quickly.
-Stormy
DO NOT ARCHIEVE
Message 11
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Subject: | Re: Antennas general |
Dale, you may have something there... ask the patent office ;-)
do not archive
-----Original Message-----
Sent: Thu, 27 Jul 2006 7:13 PM
Are you sure it is not E=mc2 ;<)
Aw, shoot! Make that P=E^2/R. I knew better than that. Hit "send" too quickly.
-Stormy
DO NOT ARCHIEVE
________________________________________________________________________
Message 12
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Subject: | Off line for a few days |
--> AeroElectric-List message posted by: "Robert L. Nuckolls, III" <nuckollsr@cox.net>
Dr. Dee and I are loading the van up with aunt Sally and uncle
George tomorrow morning to go poke around in the mountains for
a few days. Got tickets for a steam-powered narrow-gage ride
on Saturday. After that we'll probably go explore New Mexico
ghost towns . . . or something equally un-stressful.
We'll be back Wednesday, August 2.
By the way, Eclipse got their provisional type
certificate issued at OSH a few days ago. As far as I know,
that's the first instance of networked, multiple smart
actuators being used on flap system of any GA aircraft.
Yours truly had a role in the architecture and development
of that system . . . I'm still hopeful of getting this
technology onto Premier before I retire. It's about half the cost,
20 pounds lighter and best yet - works as advertised
Bob . . .
---------------------------------------------------------
< What is so wonderful about scientific truth...is that >
< the authority which determines whether there can be >
< debate or not does not reside in some fraternity of >
< scientists; nor is it divine. The authority rests >
< with experiment. >
< --Lawrence M. Krauss >
---------------------------------------------------------
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