AboutMarc Ebelini Expertise Basis aircraft and engine maintenance. Avionics and other electronic questions related to computers and radio communications.
Experience FAA licensed comercial pilot, A&P mechanic, former authorized inspector, ground instructor certified in aircraft, powerplant and radio navigation. FCC commercial license.
Expert: Marc Ebelini Date: 5/13/2008 Subject: AMTENNA ON AIR FORCE ONE
Question ON THE LOWER SIDES 0F THE OLDER AIRFORCE ONE VC-137B THERE ARE WHAT APPEAR TO BE ANTENNAS THAT ARE DONUT IN SHAPE BUT FLAT. ONE END OF THE DONUT LOOP IS WIDER THAN THE OTHER AND THE THINNER END ENTERS THE FUSELAGE THROUGH WHAT MIGHT BE AN INSULATOR FEED THROUGH. I WAS TOLD THEY ARE TV ANTENNAS. I HAVE A PICTURE OF THE DEVICE. ANY IDEA WHAT THE ARE AND WHERE I MIGHT GET SOME FURTHER INFORMATION.
THANKS - JOHN
Answer Finally received a challenging question. So challenging I am hesitant to respond. Remember there are numerous pieces of equipment aboard that aircraft both transceiving and plain receiving. While the size can usually determine the frequency range that too can be misleading.
Case in point. Atomic wrist watches use a 60 KHz signal from Colorado to maintain it's fantastic accuracy. Transmitting antennas are usually 1/4 or 1/2 wave in length. Now the wave length for that frequency would be 300,000/frequency in KHz. Results is in meters. So how does that wrist watch pick that low frequency with an antenna so small in comparison to the wave length? So now I have you thinking. If the shape is donut or round could mean it's omni direction. Also as the aircraft moves toward it's target the signal get's stronger so the design may require greater signal strength aft. It's all speculation. So why don't you just email the picture at ortelho@aol.com and I will forward it to my friend at the Pentagon to see if he is allowed to reveal it's actual use.
The Polaris submarines once used a 10 KHz signal for navigation (you do the math on the wave length.) Yet I stalled an antenna the size of a brick on an aircraft to receive the signal. The Canadian government was interested in using that method for aircraft instead of installing VOR stations through out the country because of the cost of installation and maintenance. Who knew GPS would not be far behind.
Send the picture and give me a few days to see if I can give you the exact answer instead of speculating.
