Hidden stealth aircraft antenna

wsuffa said:
Same here. And when the Tek 7L12 & 7L13 were the "standard" that even the FCC used.
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Those were significantly newer than the HP 141T. We used a 7L13 when I worked for the Navy in the late 1970s. I really like the HP 8566A Spectrum Analyzer. A boat anchor (112 pounds, IIRC), but there was a button for every function. Easy to program over the GPIB interface. Not a menu in sight. Did I mention that I hate menu driven instruments?
 
Ghery said:
Those were significantly newer than the HP 141T. We used a 7L13 when I worked for the Navy in the late 1970s. I really like the HP 8566A Spectrum Analyzer. A boat anchor (112 pounds, IIRC), but there was a button for every function. Easy to program over the GPIB interface. Not a menu in sight. Did I mention that I hate menu driven instruments?
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Yeah, I used both... Well all 3. I agree about the storage on the 141T, but it had a plug-in that did baseband well, the 7L units were RF. Moved on to an Anritsu with digital storage later, I do like the Anritsu stuff. I cut my teeth on the 7L13 for RF and the 141T for baseband.
 
As someone whose radio knowledge limits interaction with one to turning it on, tuning to the desired frequency, and adjusting the volume, I find antenna discussions fascinating.

:D
 
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I'm the OP here - I learned about graphical VNA's, have purchased one, and am having lots of fun generating graphs of the SWR across frequencies for my existing antennas. I'll use it when developing the com antenna for the Tailwind. I have determined that a wing strut is within a few inches of being the recommended 3/4 wavelength for the long element of a J-Pole at 127 MHz - I'll see what I can do with that ...
 
If you can figure out how to model it (and most things CAN be modeled), the MiniNEC or NEC do a pretty good job of predicting antenna performance. Takes some time to learn, but once you do, the info is very useful. There are a couple of packages that are focused on the ham radio community that put a more user-friendly front end on the software.
 
Yes, I've used 4NEC2 , but this time I'll do it empirically, since I have a new tool to play with!
 
Super old thread. Probably newer threads that I'll search out but this happened to the first I saw.

Most of the content flew by at an flight level above my operating levels, but some what similar to a few of the posts, I'd like to ask how possible it would be to get good transmit and reception from a 1/4 wave antenna mounted vertically inside a cub type tail.
- Yes, it's a chromoly steel frame.
- A sizeable ground plane would be problem, at least in width.
- Could be quite long, meaning, may be able to fit a 1/2 wave? Does that help or hurt?
- And quite close to vertical in flight attitude.
- Could "house" it in a pex tube mounted to the fuselage.

Is the tail "open" enough to allow it to work well?

Thank you.
pb
 

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If the rudder was open internally, I suspect that while you might get "ok" performance to the sides, range will be very poor along the longitudinal axis of the plane (straight in front and behind). But passing the antenna through the ribs as well, who knows what would happen, the reflected RF might even damage the radio.
 
flyingron said:
The first statement that an "antenna will radiate just fine regardless of length" is bunk.
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I have several antenna books by people who design antennas for a living that would disagree with you.
 
Pinecone said:
I have several antenna books by people who design antennas for a living that would disagree with you.
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They either design lousy antennas or you didn't understand what they say. WeirdJim (now gone from the forums) who designed radio and antenna systems for a living agreed with me earlier on in the thread. You can match a steak knife to the radio and but it's not going to radiate optimally.
 
Pinecone said:
Exactly. You can match anything and it will radiate most of the power (minus some feedline losses).
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Balderdash! There are many competently designed antennas which operate at well below 50% efficiency due to size and cost considerations. An aviation related example is the NDB transmitting antenna. Here is a link to a paper describing one:


The beginning of the paper describes the design considerations and tradeoffs and there is an example at the end which has all of 19% efficiency.

I suspect the aforementioned "steak knife" used a VHF comm antenna would be similar.
 
There is considerable difference between using a 20 ft. antenna for a frequency whose ¼ wavelength is 600 ft. and an 11" (steak knife?) one for a frequency whose ¼ wavelength is 22".
Two days ago I "worked" a station in Hungary from OK using a 550 ft long wire loop on a frequency whose ¼ wavelength is 24.5 ft. with 2.8 watts of RF to the feedline. True, the current digital communication protocols are VERY efficient, and it was text, not voice.
The point being that you can't make blanket statements about antennas that will or will not work without knowing the details. That having been said, I am not going to mount a VHF comm antenna inside my steel tube fuselage.
 
OKDonn said:
There is considerable difference between using a 20 ft. antenna for a frequency whose ¼ wavelength is 600 ft. and an 11" (steak knife?) one for a frequency whose ¼ wavelength is 22".
Two days ago I "worked" a station in Hungary from OK using a 550 ft long wire loop on a frequency whose ¼ wavelength is 24.5 ft. with 2.8 watts of RF to the feedline. True, the current digital communication protocols are VERY efficient, and it was text, not voice.
The point being that you can't make blanket statements about antennas that will or will not work without knowing the details. That having been said, I am not going to mount a VHF comm antenna inside my steel tube fuselage.
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Curious to learn what worked on your Tailwind. Have used 2 inch copper tape with sufficient bandwidth.
 
Rebelrabbit said:
Curious to learn what worked on your Tailwind. Have used 2 inch copper tape with sufficient bandwidth.
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I'm sorry to report that my Tailwind is not to that stage yet -- but I'm hoping to load a wing strut similar to a J-pole antenna. I'll report when I try it.
 
Farmboy said:
Can you elaborate?
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There are several reasons not to mount a transmitting antenna is a steel cage. First, all of the steel tubes will interfere with the transmitted pattern and de-tune the antenna to increase the SWR (power reflected back to the transmitter, not radiated from the antenna). Second, the firewall at the front of the aircraft (assuming a tractor configuration) will block the signal to the front.
Yes, some signal will get out, but there will be many areas where it's blanked, and what does get out will be attenuated.
Depending on your flying, this might not be a problem, or it might be a big problem.
 
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