What's under the shark fin?

The VHF TX range stops at 137 MHZ in the air craft band. The ham band begins at 144 MHZ the only antenna that would have a wide enough band width would be a folded dipole and at best it's only good for 13 MHZ. This would not be a good air craft antenna because it would only be resonate in the upper part of the air craft band. It would put you inside of the ham band but in order for it to be that wide it would have to be 1/2 wave and that's a good bit too big and ugly for mobile use. Generally the widest a vertical ¼ or 1/2 wave antenna will do is maybe 4 MHZ. I can match and antenna that is way off in the ham bands with a tuner unfortunately this only fixes the mismatch and makes the radio happy it does not make the antenna resonant so its efficiency suffers. The other issue with anything air craft is expense so you can figure whatever you want to do with antennas will be 4X the price with an FAA sticker on it.

 

I would agree that the FAA sticker raises the price dramatically. I would not agree on the frequency range for transmit that were stated. Again the best advice is to contact the antenna manufacture directly. I am showing several "shark fin" aircraft antennas on manufactures websites listed with all of the OP's original freqs in the operational range. Tim I don't have the experience in the HAM radio that you obviously do. Can you share your expertise. I have no desire to lead the OP or anyone else down a road that will not help them archive their desired goals.

 

I did some research on air craft antennas because I was not really sure how they got such a wide band width. In some cases they were dual antennas (two antennas of different freq inside of one unit) In with two feed lines and in other cases it was a single dipole 19 MHZ wide. There also seems to be two completely different antennas for the low edge of the air craft band i.e. VOR from 108-118 and the rest from 118 to 137MHZ. 19 MHZ is doable with folded dipoles but again it stops at 137MHZ. On the down side they are in the $1,600 range! (IIT Communications DM C60-1 118-137 MHZ) it is a shark fin type fixture. Here is a picture of an HF band antenna tuner this tuner would work in both the armature bands and in the HF aircraft bands again the air craft tuner would probably come close to the price of a good used car. It is designed to tune random length wire something you would see on a long haul air craft or any air craft out of line of line of sight VHF communications. They were usually strung from the tail forward. Basically it uses combinations of capacitors and inductance to make the wire resonate on the desired freq. In the case of air to ground VHF communications you do not need a lot of antenna because the aircraft acts like a very tall tower increasing its range dramatically. I have talked to pilots that were hams using their armature hand held radios 200 miles away!

 

http://www.sti-co.com/ makes some stealth antennas. I use a bulkhead type feed through on my fiberglass cap for the 2 meter HIQ loop for SSB that is mounted on a roof rack. Generally for the roof I use NMO mounts have a 900 MHz and GPS antenna mounted on 2 of them. Removing the shark fin and replacing it with a NMO mount might work, needs a 3/4 inch hole. Plugging the alignment hole could be as easy as using a rubber plug. HRO sells some for when you remove an antenna, I am sure they are available elseware.

 

I agree the circuitry required to match a trailing wire or fixed wire HF antenna to an amateur radio is cost prohibitive and not the right idea here. I believe that a few of the options I was seeing were dual element antennas and are rated for the entire frequency band the OP asked about. I am not aware of a manufactures design that would stop the antenna from transmitting at the other frequencies. My experience is that our airborne radios were electrically and or mechanically locked out of FCC regulated bands but that these could be overridden and the bands could be transmitted on in some cases. This all depended on the specific radio and circumstance. My point is that I do believe you can find a suitable aircraft antenna for what the OP wants. It will likely be expensive, and therefore cost prohibitive.

 

Any antenna will TX out of band that's not the problem it is the match, an out of band antenna will demonstrate high SWR modern radios will only operate at full power with a match of 2:1 or less any thing above that and they start to cut back on power and if it's bad enough they will shut down all together. By the time you get in the repeater frequency of a ham VHF radio you would be almost 10 MHZ above the design range of the antenna so the SWR would be too high for the radio to tolerate.

 

Again not for the antennas I found on line that specified that they were designed for the entire range the OP requested.

 

If you would kindly PM me the site I would love to see it.

 

Me too! I've been following the discussion and $1600 would be out of my range for a tiny antenna.

 

When I get some time I will look for it again. Iggy, the price on any of these aircraft antennas are going to be higher than what you are comfortable paying. I would expect at least $1,000. Originally I was hopeful that depending on the frequencies involved you could indentify a commonly used antenna and maybe find a used one off of an aircraft that has been taken out of service. The idea has obviously been debunked as not practical. As for finding an antenna that will function that is the easy part. Finding one that will fit your budget that is the hard part. If these antennas were easy to locate and cheap to purchase every HAM operator would have one. They don't for a reason. Not because they don't exist but because they are expensive. I have thrown more of these away over the years than I can count. We use to list them as consumable and there fore stoked and tracked them like a screw or washer. Over the years we recognized that they are expensive to be treated that way. But we still throw them away as they really can't be repaired economically and effectivly. Long and short if you want me to send you a link for the site I will look for it again, but as I have said several times it will likely be price prohibitive.

 

The price to me is not important it could be $5 and I still would have no use for it. I just want to see how it is that broad banded. After playing with hundreds of antennas I may just learn some thing new.

 

I got back from my thanksgiving trip and thought I would look up this antenna thread again... Here is a link to the local aerospace manufacture's website and a list of the antennas they manufacture. From what I can see many are rated to operate in the entire band with the OP originally asked for. I am not sure what the pricing would be but again I suggest interested parities contact the manufacture directly to get specific questions answered. http://antcom.com/documents/catalogs/UHF-BandAntennas.pdf

 

Yes there are a few that would work in the armature bands. The listings cover a huge range but if you look there are different antennas in each broad range nothing that covers top to bottom. They are a bit broader than I thought not sure how they do it would like to see the antenna drawings and an SWR curve. It’s real hard to make an antenna that covers 20 megs until you get into microwave.

 

No Tim there are several antennas that cover a couple of hundred Meg's. Just because you are not familiar with them does not mean they don't do it. You asked for a website that lists them and I provided that for you please stop discounting the information provided. The 5th, 6th, and 7th antennas listed state they function in the entire range the OP asked for several hundred Meg's of coverage.

 

Thank you for the information it was wanted to know so I could research it. I wanted to is how they did it not to argue with you, they are called strip line antennas in essence they are multiple antennas inside of the housing on a flat foil base there is a lot of science involved there. This is why they fall into the amateur bands because of the interactivity of the multiple antennas otherwise there would be no reason to do so it would be of no use to them. My contention was no single antenna was capable of being that broad banded. I use a fan dipole of different lengths with a single feed point on the HF bands that covers a wide range of frequencies one antenna alone would not be able to do that. So what happens the frequency selected takes the path of least resistance and only uses that portion or portions of the antenna that are resonate. Bottom line yes they would work in the amateur bands but not particularly practical.

 

I understand the science behind the antennas and their use. Remember I was the one that stated they existed all along. I am not sure why now that you realize they exist and function in the freqs that you thought were impossible you would state that they are impractical. I would suggest anyone that wants to see if these could be used for a specific application consult the manufacture and not take the word from someone on a forum they have never met.

 

Well good for you I bet you can even tell me that at one point the FCC was thinking of taking frequencies away from the ham VHF bands and giving them to the aviation bands I found that out from a commercial pilot who is also a ham that is why they were made to operate in the ham bands. Then of course you would also know that due to the changes in nav aids they didn't because the now use the lower end of the band for voice. Then you would also know that they are dropping AM for SSB to further enhance the band width instead of taking up 12.5 KC on each channel. I had no idea how they made the antennas once I found out they were that wide thinking it was a single antenna. I'm guessing you didn't either or would have told me that they were a multi antenna system in one package that would have been easy. I could understand that because I use homemade multi antenna systems. One antenna alone is not capable of frequency’s that wide now I see what they were doing and the reasons why are obvious instead of having several antennas to ice up. I learned something how about you?

 

Tim I have learned about ham radios and people on the net, antennas, not so much... I stopped studying them about 25 years ago as I learned what I needed to do my job. I am glad you learned something. I am not looking to argue but would suggest that before any of us tell others that things don't exist or are impossible that we first ask them to explain how. You could easily have typed into Google UHF/VHF antennas and found the same info I did for the the OP and yourself. Instead you choose to repeatedly state how wrong I was. As for the current changes in aviation frequency uses I can't speak to those, I retired from avionics in 2006. From what I know and experienced on the platforms that I maintained and taught for the NAVY, I would be surprised to see more frequencies go to the civilian sector as our need for band with and connectivity was ever growing and increasing. We had 6 UHF/VHF radios, 2 HF radios, Satellite communications, and several other data systems that use different frequency spectrums all operating at the same time. I could be wrong, the government does some crazy things. Either way I mean no harm to you or your reputation but I did feel as though you took an offensive position against the assertion I was making that these types of antennas could be a viable option for the OP. Again no harm no foul best of luck to you in the future.

 

normally a shark, right?
something like this