REFLECTOR: Antennas

Wed May 22 15:39:17 CDT 2013

Dick,

The provided antenna is a ground plane antenna.  They give you the antenna and you are to supply the ground plane.  The ground plane elements are called radials as in radius.  An 18" antenna needs 18" radials.  Four conductors spaced at 90 degrees and 18" in length meet this requirement and will work as well as a 36" diameter disk.  Installing without a ground plane is only 1/2 an antenna and will perform badly.  The manufacturer says that this is the only antenna certified to be used with this unit because it's the only one they used to certify the unit, not because it is good for use in a glass plane.  The FAR's require that the ELT antenna meet the required RF radiation.  I bet your local avionics shop has a procedure for that.  I have a dipole, copper foil antenna on the back side of the pilot side center spar that my field strength tests show it to out perform any whip on a spam can that I've checked.  I have the old 121.5-243 Mhz ELT but I could modify the antenna to accommodate 406 Mhz.

Larry Coen
N136LC

From: Dick Harpster 
Sent: Wednesday, May 22, 2013 12:12 PM
To: 'Velocity Aircraft Owners and Builders list' 
Subject: Re: REFLECTOR: Antennas

I talked to an engineer at Steinair, who built my panel. His recommendation is to install the antenna horizontal, along the wing spar. It will require a ground plane, preferably the same length as the antenna. I check and by installing the antenna on a piece of 2” x 1/8” aluminum bar, I can use a 20” piece at the end of the wing spare where the wings bolt on, pointing back towards the fuselage. 

Dick Harpster

From: reflector-bounces at tvbf.org [mailto:reflector-bounces at tvbf.org] On Behalf Of Brett Ferrell
Sent: Wednesday, May 22, 2013 12:17 PM
To: reflector at tvbf.org
Subject: Re: REFLECTOR: Antennas

I haven't done any testing, but for reference mine was vertical, and had to get past the SS on the firewall and through the hangar, and the USAF was ringing every phone I own in milliseconds asking awkward questions, so I know up-and-down works fairly well.

http://www.velocityxl.com/attachment.php?attachmentid=4849&d=1276866122

-- 

Brett Ferrell

On Wed, May 22, 2013, at 11:33 AM, Keith Hallsten wrote:

  Brett,

  I had considered placing the dual-band 406/121.5 ELT antenna in front of the firewall, but thought the stainless steel sheet would distort the radiation pattern so badly that there would be no coverage to the rear at all.  I was therefore considering mounting the ELT antenna laying horizontal in the back of the strake, along the spar.  I realize that you would normally want it vertical, but figured the pattern distortion would be less than it would be up against the firewall.  Has anyone done any relative testing of those two (compromise) locations?

  Keith

  From: reflector-bounces at tvbf.org [mailto:reflector-bounces at tvbf.org] On Behalf Of Brett Ferrell

  Sent: Tuesday, May 21, 2013 5:12 PM

  To: reflector at tvbf.org

  Subject: Re: REFLECTOR: Antennas

  Yep, and these work... I installed one of the standard fiberglass antennas behind my false bulkhead and accidentally tripped the ELT... it the satellite even inside a metal T hangar...

  -- 

  Brett Ferrell

  reflector at velocityxl.com

  On Tue, May 21, 2013, at 07:51 PM, Bachman, Jonathan wrote:

    The new 406 MHz ELT system is what I was going for

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    From: reflector-bounces at tvbf.org [reflector-bounces at tvbf.org] On Behalf Of nmflyer1 at aol.com [nmflyer1 at aol.com]

    Sent: Tuesday, May 21, 2013 3:16 PM

    To: reflector at tvbf.org

    Subject: Re: REFLECTOR: Antennas

    Jon, 

    It is the same as building the comm antennas as per the plans in the factory manual. Since it sits smack in the middle of the VHF com band, it is adequate. Since I haven't crashed yet, and I don't have a SWR meter, I relied on the old standby method of checking the ELT. 

    Here it is:  

    "There are two ways to test for sufficient antenna signal on a C91a ELT. One is to evaluate the signal strength using a test box like those made by QCAvionix or Whiffletree. The other method is to listen to the signal using an AM-band radio receiver.

    The FAA endorses the AM radio test and has codified this check in the most recent update of Advisory Circular 43.13-1B (CHG 1). The test for sufficient signal radiated from the antenna is as follows (Par 12-22):

    "Active the ELT using the ON or ELT TEST switch. A low-quality AM broadcast radio receiver should be used to determine if energy is being transmitted from the antenna. When the antenna of the AM broadcast receiver (tuning dial on any setting) is held about 6 inches from the activated ELT antenna, the ELT aural tone will be heard."

    "It has to be a cheap AM radio," said Bob Glorioso, president of QCAvionix. "It can't be too well shielded. You're trying to overwhelm the AM detector."

    Many mechanics, perhaps unaware of the FAA's recommendations, listen the ELT signal on the aircraft's VHF radio, set to receive on 121.5 megahertz. But this isn't a good test, because the aircraft radio's receiver is extremely sensitive. The AM radio test, says AC43.13, "is not a measured check; but it does provide confidence that the antenna is radiating with sufficient power to aid search and rescue. The signal may be weak even if it is picked up by an aircraft VHF receiver located at a considerable distance from the radiating ELT. Therefore, this check [VHF radio] does not check the integrity of the ELT system or provide the same level of confidence as does the AM radio check."

    What the FAA is saying is that simply listening to the ELT signal on the aircraft's VHF radio does not meet the requirements of 91.207(d). "

    Now if you wanted to change to a 406 ELT, you would have to find the correct antenna lengths, but the idea should be the same. 

    Kurt 

    -----Original Message-----

    From: Bachman, Jonathan <jonathan.bachman at mtsi-va.com>

    To: Velocity Aircraft Owners and Builders list <reflector at tvbf.org>

    Sent: Tue, May 21, 2013 2:53 pm

    Subject: Re: REFLECTOR: Antennas

    Kurt,

    Do you have any more specifics?  I have a STD RG and am thinking of upgrading to the new ELT freq.  But the thought of adding an external antenna is holding me back.  Does the antenna you made perform adequately?  

    Jon

    N956DR

----------------------------------------------------------------------------

    From: reflector-bounces at tvbf.org [reflector-bounces at tvbf.org] On Behalf Of nmflyer1 at aol.com [nmflyer1 at aol.com]

    Sent: Tuesday, May 21, 2013 2:33 PM

    To: reflector at tvbf.org

    Subject: Re: REFLECTOR: Antennas

    I just made one similar to the com antenna. Put it on the inside of the fuselage aft near the gear bulkhead area. 

    Kurt 

    -----Original Message-----

    From: Dick Harpster <Dick-CentralSecurity at nc.rr.com>

    To: reflector <reflector at tvbf.org>

    Sent: Tue, May 21, 2013 2:09 pm

    Subject: REFLECTOR: Antennas

    I am currently building an XLFG and am looking for advice on antennas. I of course have the nav / com antennas in the winglets and did the marker beacon in the floor. My problem is I can’t seem to find a ELT antenna that will work internally and I sure don’t want that ugly 18” whip on the outside of the plane. With the new frequency, none of the internal antennas are recommended.  Any advice?

    Dick Harpster

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