REFLECTOR: Antennas

Tue May 21 16:16:47 CDT 2013

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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