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oldbaldyman
14-05-10, 18:07 PM
Having a sub115kg trike means the locations for radio aerial are severely 'limited'! Currently I use a 'handheld' mounted on my kneepad with the 'rubber duck' protruding from the radio. Frequently this installation causes a loud 'whistle' on transmit. Assuming the whistle to be feedback into the microphone I have reasoned that mounting the antenna as far away from the microphone as possible would cure the problem. To that end I was very interested in a recent Microlight magazine article on a Kingpost mounted 'V' antenna from South Africa (AirMagic Vee Rabbit). Question is - has anybody in the UK got one of these and if so could you tell me if its as good as the article (and AirMagic) claims?

VinceG
14-05-10, 19:42 PM
Well in answer to your question yes and no.

We got three delivered and although one was great, one was delivered broken and the other is crap, and the level of service from the uk dealer was to wash his hands after the sale, don't waste your money. Get something from a reputable dealer wherever you are.

andy dixon
14-05-10, 20:39 PM
i am the one who does the product testing for this site obviously under the supervision of vince, to start with it was 240 quid wasted, one came broken and when i sent it back to them recorded delivery, twice, both times they refused to sign for the package,about 40 messages left at the guy's airfield (where he is a gyro instructor) but still no reply, sent a letter to south africa to the manufaturer........no reply.
the manufacturer is ZULU 1 on this site,so i sent him a couple of e-mails.........you guessed it......no reply.
so 1 knackered on delivery
1 totally rubbish
1 works
i wrote the article in the hope that it was just teething problems with manufature.......obviously not,
a store that advirtised them was due to stock them upon import ,had advanced paid orders for 57 units, plus 9 from our airfield and 7 for the airfield next door all within a week of the article being written,the guy at the shop looked a bit sick as he returned everyones money

ZULU 1 must be a real rich man if he wasn't bothered about advanced orders of 5,840 quid

my advise is buy a microavionics di-pole antenna,i've bent mine in two a million times and it just springs back streight every time,and the warranty back-up service from microavionics must be the best i have ever come across in my life,and ultra quick if you do have any problems
their turnround time on a repair is usually 1 day or if you're in a rush they will do it the same day..........now that kind of service gets my money every time !

Bob T
14-05-10, 20:46 PM
Andy, as the product tester, have you managed to test the BioniX yet? Derek and I have!

andy dixon
14-05-10, 20:54 PM
i don't just want to test one........i want one to keep
when the bloke invented the wheel everyone must have looked at it and thought "thats so obvious" then everyone made carts with wheels on instead of skids.
one day soon i'll be round with my long toungue to give it a good lick !

VinceG
15-05-10, 17:19 PM
one day soon i'll be round with my long toungue to give it a good lick !

Hehehe you do make me chuckle :D

truthseekers
18-01-12, 00:39 AM
Just bear i mind these may be incorrectly aligned according to manufacturers instructions as any aerialon this freuncy that wants to transmit out to the horison should be aligned vertically - one antenna up and one antenna down. The manufacturer suggests both antenna up and ive spoken to someone called Paul from the company who is suggesting the reason for that is not due to performance of the aeriel but do do with it fitting better on the kingpost.

Clearly you will be better off with it in the vertical alignment but I dont own one so dont know what to suggest in altering the fittings to make it happen. May just be a case of swapping over some bolts.

VinceG
18-01-12, 01:20 AM
Matt. Paul's a member on here AKA Zulu1.

Welcome to the forum :D

truthseekers
18-01-12, 16:35 PM
a recent Microlight magazine article on a Kingpost mounted 'V' antenna from South Africa (AirMagic Vee Rabbit). Question is - has anybody in the UK got one of these and if so could you tell me if its as good as the article (and AirMagic) claims?

Can you remember which magazine it was in and which month. I am interested in seeing the review.

MadamBreakneck
19-01-12, 14:58 PM
I use a 'handheld' mounted on my kneepad with the 'rubber duck' protruding from the radio. Frequently this installation causes a loud 'whistle' on transmit.

I've used a simlar setup with no problem in the past. Are you using Lynx hgear? I believe there is a certain combination of kit (can't recall without checking their data) which gets feedback like you describe. They sell a filter which resolves that completely.

Joan

PS. just looked it up http://www.lynx-avionics.com/English_Site/E_Site_Technical/E_Instructions_Pdf_files/e_026_0_radio_power_filter.pdf

AndyJ
20-01-12, 13:43 PM
I've recently bought an aerial from Flycom, the performance is very good and the guy that runs it is a real gentleman. The service is superb.
The product arrived well packed, very quickly and the price is to my mind very good. For this sort of thing I prefer to stay with tried, tested and functional. I think many bought V-Rabbits because they look flash!

AndyJ
20-01-12, 13:44 PM
I've recently bought an aerial from Flycom, the performance is very good and the guy that runs it is a real gentleman. The service is superb.
The product arrived well packed, very quickly and the price is to my mind very good. For this sort of thing I prefer to stay with tried, tested and functional. I think many bought V-Rabbits because they look flash!
Link attached http://www.flycom.co.uk/

truthseekers
20-01-12, 20:23 PM
I tested out the range of Flycom headsets and intercom at Popham airshow. The first thing I noticed was narrow range frequency response and sounded tinny to me. No good for in air music. Next thing I found was that they didnt cut out much outside noise for my liking. I must say these seemed like the first attempts at what Microavionics was producing when it started. I think Flycom has a way to go yet. Flycom offers no "high end" range with noise cancellation - just boasts its helmet + headset combo is good. No use to 3axis users though and their headset is basic - uses the same Pelot ear defender as Microavionics.

(warning dot be fooled by Flycom saying "noise cancelling mic" - this is just a standard low noise similar type as used also in microavionics low end range. Its not got any clever type of noise subtraction circuitry nor ANR and squelch as far as I am aware. Please correct me if I am wrong.

I love my microavionics ULM200 with noise cancellation and auto squelching - I can hear myself think now when flying rather than hearing the engine noise amplified through the always on microphone ;-) Now I know what people are saying rather than hearing them speaking and the noise of my engine mixed on top - now with the ANR and squelch its just them speaking until I say something and then I do hear engine noise briefly when the squelch opens.

Having tried out the Flycom range and Microavionics range prior to buying I could tell Microavionics was better clarity for me.

As for antennas - a whip is a whip. Flycoms antenna is the same as Microavionics and many others just a piece of metal on a piece of RG58 cable with a BNS on the end of it. This is the most basic and undeveloped type of aerial there is. The length is 570mm which makes it what is known as 1/4 (quarter) wave.

The V antenna (and the one I am making at the moment) is 5/8 (five eighth's) wave which actually has more physical metal picking up more signal as its longer. So before you even start theres why cheap 1/4 whips whips dont do so well. Add to the fact that the V antenna is propagating more signal around it in a donut shape - more out to the horizon less to the ground and sky - makes its transmit and recieve signals stronger by a 2x factor than a standard whip.

So basically its 1x signal versus 2x signal. Also the standard whip lengths may still need to be tuned which requires knowledge of SWR meters and stuff -else you could be transmitting a load of reflected signal which either heats up your radio (and can kill it) or wastes lots of signal into the cable. Its a science and for best results its a good idea to consult those who have done a lot in this area as it is not good to just buy and aeriel and screw it on and think way-hay.

There will be little or no difference in Microavionics aeriels performance over flycom except flycoms is 20 cheaper (30) - microavionics costing 51 from Transair as an example. For this reason I would buy flycoms and save - but really there are a lot better aeriels out there than these 1/4 wave basic model ie V Antennas ;-)

Flycoms intercom comes in two flavours - just a box with no frills or the other model bolts on to the back of the radio. I am sure someone out there likes these but for me having oodles and oodles of wires hanging out of my radio with Jacks (which easily pull out - theres no locking mechanism) compared to locable 1 piece connector from Microavionics - Flycoms harking to old GA days with two jack wires and two times as much frustration getting them plugged in the right way around and twice as much fumbling getting them plugged back in again if they come out during flight. Each to their own on this - yes you can use your headset in GA - but lets face it how many times has that ever happened? What is used in your aircraft tends to stay in your aircraft and when you meet someone with GA sockets he tends to hand you a pair of his (or hers)... So I think in tiny microlight cabin/trike environment lots of unlockable jack plugs just isnt where microlighting is at right now.

The phone adapter from flycom is similar to the portable stuff from Harry Mendehlson. You can easily break off jacks too - so having lockable flying leads (push twist) seems much more sensible over jacks. Jacks are for the expanse of a GA cockpit IMHO and not for under seat fitting or being slipped in side pockets.

goflygaz
20-01-12, 21:55 PM
I tried Flycom and Microavionics and chose the Flycom - much comfier with no pressure points like the MA ones - great for passengers as the memory foam adapts to more head sizes, and they are super quiet. The MA VOX is good, but a total faff, constantly needing adjustment when changing speed, voice getting clipped when you slow down for circuit and dont re-adjust - just a complication thats not needed - since with the volume set on the Flycom - its perfectly quiet enough.
I believe a couple of chaps have fitted MA electrics into the flycom helmet - great but expensive!
As for the Jack plugs - no chance of pulling them out or breaking them off - not unless your standing on them to tighten the hangbolt!
the MA/Lynx twist connectors can also be a faff, they are more exposed to the elements and not waterproof - seen a few corroded ones too.
I can plug the Flycom Jack plug in with my gloves on - can you connect the MA/Lynx ones with a gloved hand???

so whilst you make some valid points, there are some very biased ones too!

truthseekers
21-01-12, 00:23 AM
I tried Flycom and Microavionics and chose the Flycom - much comfier with no pressure points like the MA ones - great for passengers as the memory foam adapts to more head sizes, and they are super quiet. The MA VOX is good, but a total faff, constantly needing adjustment when changing speed, voice getting clipped when you slow down for circuit and dont re-adjust - just a complication thats not needed - since with the volume set on the Flycom - its perfectly quiet enough.
I believe a couple of chaps have fitted MA electrics into the flycom helmet - great but expensive!
As for the Jack plugs - no chance of pulling them out or breaking them off - not unless your standing on them to tighten the hangbolt!
the MA/Lynx twist connectors can also be a faff, they are more exposed to the elements and not waterproof - seen a few corroded ones too.
I can plug the Flycom Jack plug in with my gloves on - can you connect the MA/Lynx ones with a gloved hand???

so whilst you make some valid points, there are some very biased ones too!

I am perhaps biased but its because its what ive grown to like - so yeah a bias ;-)

The VOX on my MA is very solid - turn it up to find the right point and a little turn more and its set. Opens perfectly when I speak and closes afterwards. No different engine settings upset mine at all, but I am in a cabin on a 3axis so maybe this helps.

When I was flying flex I did have issues with Jacks coming out and I hated them to the point where I scrapped my working system for the MA to benefit from an easy locking system. Yes I could do it with my gloves on push and twist is easy. However taking my eye off the ball to work out where a jack went into and having to grab the intercom and hold it in my field of vision to put the plug in wound me up and I had to take my hands off the bar or hold the bar in messing about. In my 3axis i think it would be easier as it will fly happily hands off, but certainly something that frustrated me in my flex.

I dont remember trying Flycom Memory Foam earpads but yes that does sound very nice indeed. My MA do sit on my head well but after a couple of hours I have usually moved them around a bit. The worst bit is my glasses, they dig in badly but I find if I take the time before flying to make a good position then I dont notice them later.

Do you know if you can get these memory foam bits independently as I fancy fitting these to my MA if they can be found.

I just speak as I find. I am not a sales person for any of these companies and IMHO think they all charge waaaay too much ;-) Seeing as you are certain Flycom are great I will take the time out again at another airshow to try them out and see if they have improved.

goflygaz
21-01-12, 10:50 AM
I think we are talking about slightly different issues.
Since you are comparing flex with 3 axis. I was talking about the Flycom integrated helmets, whilst I think you are talking about headesets only.

Speaking from a flexwing point of view, the Flycom integrated helmets are the comfiest and warmest of the lot, the MA ones dont even come close. ( but I share your opinion that the cost of all of them is OTT) The memory foam I was refering to is in the helmet - not the headsets.

The VOX in the flex open cockpit seems to need constant adjustment dependant on flying speed, OK in cruise, but otherwise a pain and educating a passenger to use it is even harder - Unless you both have it set right it doesnt work of course.

The Jack plug is just not an issue - you must have had an awkward installation for it to be a problem. The one fitted to the side of the radio is perhaps not the best option.

truthseekers
21-01-12, 11:29 AM
Getting back on topic. Here is a video I produced showing the 120degree V antenna I have manufactured, total cost = 10 in parts. I will show an update when its glued up to stop moisture and fitted to the aircraft then I can do some testing. :salute:

http://www.youtube.com/watch?v=UQETJqllV08

truthseekers
26-01-12, 02:43 AM
I have completed some tests on a foul day in my microlight. Given that I could only climb to 1000ft I was very much able to speak to Bristol, Boscombe and Compton Abbas who all gave me 5 radio and reception was good with these stations. These are around 25-30 miles away. I am hoping that on a better day or above 1000ft I will be able to speak to Cardiff. My location in Melsham, Wiltshire by the way.
I created a small video of the test to the home made V antenna in use on the aircraft with radio calls. I noticed no directional issues with the aerial. The Buzzing noise that can be heard on the youtube video was present only in the video recording and not present in my headphones.

http://www.youtube.com/watch?v=D9nMgBVAg3Y

truthseekers
01-02-12, 18:53 PM
I was advised that the original V Antenna diagrams had the wrong length antennas and the antennas and pawsey stub were meant to be 21.6 not 23 and 5/8ths... I was getting high SWR and I wasnt expecting this... I am making up a second antenna with the correct lengths and will fit that soon.

Also had bad buzzing but installed a 22,000uf 35Volt capacitor and this has sorted out the GoPro a lot, the buzzing is much more subdued... but in fitting this next to my regulator I found a real BOO BOO...:think:

I found that someone who owned the aircraft before me has wired one of the two blue alternator leads to earth. WTF! This means this is the mosty likely cause of all my buzzing as the alternator is an AC radio inteference monster and some bright spark decided by earthing it to the chasis that my whole aircraft should be the noise antenna tranmitting and conducting this noise. Came home and consulted the manual and yes I am right, the AC should to to the regulator and not connect to anything else. Hehe. :shocked:

Found some quite corroded blade connectors also so its all being taken apart and put back to original spec so as to get my radio with no buzzies and my gopro with no buzzies at all.

Niceonetidy
02-02-12, 19:13 PM
I just got my vee rabbit antenna from Richard at the Microlight store. I briefly,tried it outside, and could hear Gloucester, and that is with a big hill in between the airport, and my home 10nm away.

I did not get any mounting instruction, should the vee be facing forward, v up?

Cheers,

Colin

truthseekers
02-02-12, 22:08 PM
The way the V rabbit manufacturer says to mount on trikes/flexwings is on the kingpost with v facing up. Similar to in this photo, http://www.microlightstore.co.uk/images/VeeRabbit0004.jpg however the theoretical best way to get signal is with the facing forwards which we have discussed in this thread at some length. Scroll back through... but here is my diagram on the benefits of facing forward. However witha serious bit of metal aprallel to it such as a kingpost this will mess up the signals in and out which is the reason they have opted to mount it facing upwards (hence the name rabbit ears) - here is my diagram http://www.circlemakerstv.org/wp-content/uploads/2012/01/v-antenna.jpg - but as i say on a trike probably best to go for the upwards facing. There are few ways that would also look pretty unbalanced to the eye on a trike otherwise.

Niceonetidy
04-02-12, 15:16 PM
Does anyone remove the Ears from the Vee antenna when not in use, or just leave on,

Als, do they have to be mounted on tight?

Sam
04-02-12, 16:18 PM
Instructions suggest loctite to secure them, so I don't reckon they should be removed between flights.

zulu1
04-02-12, 17:04 PM
Nice onetidy, we do not advise the whips are removed after flight as the brass studs will eventually wear with usage. The brass studs are pinned in the block and will get damaged with overtightening.. Use spanner provided and the length of the device will by design provide the correct torque of the whip. There is no further need to apply a locking compound with assembly. Thats about it, maybe apply some copper compound to the whips threads if you intend removing the whips after flight. The block is relatively substantial and will take some "stick"but it is still advisable to treat with care.

You will be satisfied with the performance and any further questions please feel free to contact me.

Cheers Paul

Sam
04-02-12, 17:10 PM
There is no further need to apply a locking compound with assembly.

Not what the instructions said Paul !!

zulu1
04-02-12, 17:34 PM
Sam, we have revised those instructions recently with fleet experience, I will email to Microlightstore for onward transmission. I apologise for any inconvenience. Meantime frying in the heat in Jhb at the Tedderifeld, take a look at microlighters.co.za for a really good shoot out of aircraft available.
Cheers Paul

Sam
04-02-12, 17:44 PM
Cheers Paul, no inconvenience as I forgot anyways, been meaning to take wing off and loctite, but I shan't bother now !
Won't bother looking at website, I'll only get depressed with your weather !! I'd fancy swapping locations with you if i was bullet proof ;-)

zulu1
04-02-12, 17:56 PM
I think the density altitude today was almost 10,000 feet, I didnt calculate it but it was over 30 degrees and take off altitude is 6,000 feet. I am a coastal type and not used to the altitude. It knocks about 18% off a 4 strokes performance...
On the coast this time of the year we get a carb ice problem with the rh at 90% plus and low temperatures in early morning of around 28 degrees. Carb fogs on the outside of the windscreen from air con...
I dont think you get these issues?

Niceonetidy
04-02-12, 18:28 PM
Thanks I wil use the spanner, and not the loctite I did not get any fitting insruction. Does anyone have a copy please?

Cheers,

Colin

truthseekers
05-02-12, 11:35 AM
Zulu1 is the manufacturer based in South Africa who can probably answer questions as to how best to mount. He may reply to you here or you can PM him.

Also:

I have some very interesting news regarding my own manufacturer V style antenna. I was getting fairly high 2.5 SWR across all bands after cutting down the antenna lengths. I had been getting 1.2 on 118mhz and 135 gave me 3 which was way too high. After cutting the antenna down getting the closest at 2 swr across the board I was confused as why it wasnt getting lower SWR across the range.

I then went to advice pages where I found some very interesting and little known news. Correct cable length is important as it can affect the SWR and power. You have to use under 31 inches or if you use more then the cable has to be cut in multiples of 31 inches. I tried and cut my cable length to 155inches and hey presto now my swr is 1.2 at 118mhz and 124 mhz and 2 at 135. I may cut my antenna down again now to finish getting 1.2 or 1.5 across the range.

This is well worth noting for those who have manufacturer made whips etc which are meant to be the correct length and working off chassis ground but are still giving high SWR - perhaps the cable length is not correct. Using less cable is helpful for keeping signals strong but the non-use of correct multiple lengths can play havoc it would seem. I am proof of this as one user - so if anyone else wants to help themselves out and experiment with this I would be keen to hear your results.

If a manufacturer tells you 2metres of cable obviously this is just for ease of cutting measurement and really you need it in lengths of 31 inches to be sure.

see this article:

http://www.challengers101.com/AntennaBuild.html

truthseekers
07-02-12, 21:08 PM
I think the density altitude today was almost 10,000 feet, I didnt calculate it but it was over 30 degrees and take off altitude is 6,000 feet. I am a coastal type and not used to the altitude. It knocks about 18% off a 4 strokes performance...
On the coast this time of the year we get a carb ice problem with the rh at 90% plus and low temperatures in early morning of around 28 degrees. Carb fogs on the outside of the windscreen from air con...
I dont think you get these issues?

We dont get the heat - we do get the rain and fog and haze and winds. Your welcome anytime ;-)

Also if we had anything in the UK at 6000ft we would probably have a lot more fun.

G-TYGR
08-02-12, 20:30 PM
If changing the cable length result in a different SWR then it is an indication that the antenna is less than ideal. The ideal antenna has a 50 ohm feedpoint resistance and is cut to be resonant at the required frequency. The SWR will then be 1:1 and it will not matter what length the cable is. If the antenna is less than ideal the coax is effectively acting as a transformer and transforming the non 50 ohm resistance at the antenna feed point so that the radio sees the required 50 ohms. The trouble is that the action is frequency dependent so the correct length for one frequency will be wrong for another. The length that gives the right match for a frequency can be increased or decreased by a whole number of half wavelengths but that length will be the actual wavelength x the velocity ratio of the coax which is around 0.66 for RG58 giving around 780mm (about 31") at 127 MHz. Rather than simply calculate the required length based on a multiple of wavelengths when any errors will be multiplied it is easier to cut the cable long enough to reach with enough extra to be able to trim up to 1/2 wavelength off without making it too short. You can then use a Smith chart to determine graphically how much to trim to give the required match. Remember though that it is only right at one frequency so higher and lower will be a compromise.



Zulu1 is the manufacturer based in South Africa who can probably answer questions as to how best to mount. He may reply to you here or you can PM him.

Also:

I have some very interesting news regarding my own manufacturer V style antenna. I was getting fairly high 2.5 SWR across all bands after cutting down the antenna lengths. I had been getting 1.2 on 118mhz and 135 gave me 3 which was way too high. After cutting the antenna down getting the closest at 2 swr across the board I was confused as why it wasnt getting lower SWR across the range.

I then went to advice pages where I found some very interesting and little known news. Correct cable length is important as it can affect the SWR and power. You have to use under 31 inches or if you use more then the cable has to be cut in multiples of 31 inches. I tried and cut my cable length to 155inches and hey presto now my swr is 1.2 at 118mhz and 124 mhz and 2 at 135. I may cut my antenna down again now to finish getting 1.2 or 1.5 across the range.

This is well worth noting for those who have manufacturer made whips etc which are meant to be the correct length and working off chassis ground but are still giving high SWR - perhaps the cable length is not correct. Using less cable is helpful for keeping signals strong but the non-use of correct multiple lengths can play havoc it would seem. I am proof of this as one user - so if anyone else wants to help themselves out and experiment with this I would be keen to hear your results.

If a manufacturer tells you 2metres of cable obviously this is just for ease of cutting measurement and really you need it in lengths of 31 inches to be sure.

see this article:

http://www.challengers101.com/AntennaBuild.html

Niceonetidy
12-02-12, 18:16 PM
Hello all,

I fitted my V Rabbitt today and wend for a test flight, I flew to Reddich, north of worcester , and called Gloucester, I got a readability 4. I must say that I'm so pleased with the performance. All my previous electrical noise, strobe, engine revs, all gone now. I would be so pleased if I had designed this system. 10 out of 10. Thank you, and highly recommended, icon A22 works good now too!

Cheers

Colin

truthseekers
12-02-12, 19:52 PM
If changing the cable length result in a different SWR then it is an indication that the antenna is less than ideal. The ideal antenna has a 50 ohm feedpoint resistance and is cut to be resonant at the required frequency. The SWR will then be 1:1 and it will not matter what length the cable is. If the antenna is less than ideal the coax is effectively acting as a transformer and transforming the non 50 ohm resistance at the antenna feed point so that the radio sees the required 50 ohms. The trouble is that the action is frequency dependent so the correct length for one frequency will be wrong for another. The length that gives the right match for a frequency can be increased or decreased by a whole number of half wavelengths but that length will be the actual wavelength x the velocity ratio of the coax which is around 0.66 for RG58 giving around 780mm (about 31") at 127 MHz. Rather than simply calculate the required length based on a multiple of wavelengths when any errors will be multiplied it is easier to cut the cable long enough to reach with enough extra to be able to trim up to 1/2 wavelength off without making it too short. You can then use a Smith chart to determine graphically how much to trim to give the required match. Remember though that it is only right at one frequency so higher and lower will be a compromise.

I am not an expert, I am simply working from available information so perhaps you may be able to advise a bit more on this. From what I understand with such a wide range as the airband its going to be hard to get very low/perfect swr on all freqs but the aim is to get it as low as possible (below 2 swr otherwise its not good for the radio). Have you had experience where an airband antenna can be low SWR across the entire specrum of airband? My recent entry into building an aerial showed different SWR coming down as I trimmed the antenna and then it shot up very high with a tiny piece more of the antenna shortening... and this was then solved by the cutting the coax trick whic brogh the SWR down again. So my question is, is it normal for it to come down nicely in progressive stages and then shoot way up when youve trimmed off another bit? I expected that it might go a little up which would indicate id reached and just gone past the sweet trimming spot - but I havent had much experience with aerial trimming. Just to see if you had some input.

By the way I just saw your youtube vid of G-TYGR... great name by the way.... and its testflight that thing was rapid on takeoff roll... impressive.

zulu1
12-02-12, 19:58 PM
Niceonetidy the Ica 22 performs perfectly with the Vee rabbit as you have realised. I am pleased that you are satisfied with the performance. Trust me over 100Hrs try, cry and fly in that product..

Anyway some advice for those building home made examples, I am happy to assist. The distance between the kingpost and the feed point is critical to the antenna impedance. The standard Vee Rabbit is exactly 50 ohms and not precise on a right angle. The cable length is not critical but the distance the whips to luff lines and other cables is quite detrimental to performance. The whips are base loaded so each pair are matched on a antenna analyser. They may not be the same physical length but they are paired. A swr meter works quite fine to test. RG58 cable is quite fine for the construction. No stubb cable matching is required if the king post spacing is utilised and the use of a stubb may in fact cause a mismatch. There are certain factors in a installation like this that is not perfect but we live in the real world..Matthew you are welcome to come over and bring some fresh ideas. We are certainly open to suggestions and will definitely build any samples that you suggest..

Cheers Paul

G-TYGR
27-02-12, 17:37 PM
I am not an expert, I am simply working from available information so perhaps you may be able to advise a bit more on this. From what I understand with such a wide range as the airband its going to be hard to get very low/perfect swr on all freqs but the aim is to get it as low as possible (below 2 swr otherwise its not good for the radio). Have you had experience where an airband antenna can be low SWR across the entire specrum of airband? My recent entry into building an aerial showed different SWR coming down as I trimmed the antenna and then it shot up very high with a tiny piece more of the antenna shortening... and this was then solved by the cutting the coax trick whic brogh the SWR down again. So my question is, is it normal for it to come down nicely in progressive stages and then shoot way up when youve trimmed off another bit? I expected that it might go a little up which would indicate id reached and just gone past the sweet trimming spot - but I havent had much experience with aerial trimming. Just to see if you had some input.

By the way I just saw your youtube vid of G-TYGR... great name by the way.... and its testflight that thing was rapid on takeoff roll... impressive.

I have just tried to send a comprehensive response and had it eaten by the system so in short as I don't fancy going through the whole lot again.

Performance will degrade above and below resonance but larger diameter elements help to minimise this effect.

When scanning frequency with the antenna analyser there are all sorts of peaks and troughs in readings which I put down to odd bits of the system and the surroundings coming in and out of resonance.

If the antenna has a 50 Ohms feed point resistance and is resonant it will have a 1:1 SWR anything higher or lower will give a worse figure. Varying the angle of the V will affect radiation resistance at 180degrees it is around 72 Ohms. I knifed up a 90 degree V at the weekend and got 50 Ohms and resonant at 127.5 mHz with a 1:1 SWR this degraded at the top and bottom of the band to 1.6 : 1 and 2.3 : 1 respectively but I was only using 1.6mm rods and probably cut to favour the top of the band.

Re G-TYGR video, glad you like it, given a bit of a headwind it's 3 seconds from brakes off to airborne, the test pilot told me he wasn't trying in the video but explained how he would have done it if he had been and it works!

Sorry for the short version the original was much more detailed.

cookiemonster
11-04-12, 21:12 PM
Hi truth seekers - great info and video r.e. home made antenna. Do have any pickies of the finished and mounted item? or videos of the fitting process. Cheers Cookie

zulu1
07-06-12, 14:38 PM
Thought you may like to see a counter poaching machine used in Tanzania, it has two Vee rabbits, we make a duplex system for these chaps with airband priority, allowing the pilot to communicate with the ground trackers and base stations etc. The small antenna on the top is for this band 136-174 mhz and the not so important airband radio is inverted. They use a VXA220 and Kenwood TK 2307. The bar PTT has two buttons one for each radio and also tracker input switch. Some pilots are now wearing bullet proof vests and considering Kevlar armour beneath the fuel tanks. Such is the tremendous success rates of these chaps.6949 They are looking for pilots with at least 200 hours plus. Planes are the Solo wings Aquilla with a 912 s motor and parachutes. Expect at least 4 hrs a day in the saddle..good eyes essential !

Contact Doug Braum <Doug.Braum at tgts.com>

Rachelivy
10-06-12, 20:26 PM
Thought you may like to see a counter poaching machine used in Tanzania, it has two Vee rabbits, we make a duplex system for these chaps with airband priority, allowing the pilot to communicate with the ground trackers and base stations etc. The small antenna on the top is for this band 136-174 mhz and the not so important airband radio is inverted. They use a VXA220 and Kenwood TK 2307. The bar PTT has two buttons one for each radio and also tracker input switch. Some pilots are now wearing bullet proof vests and considering Kevlar armour beneath the fuel tanks. Such is the tremendous success rates of these chaps.6949 They are looking for pilots with at least 200 hours plus. Planes are the Solo wings Aquilla with a 912 s motor and parachutes. Expect at least 4 hrs a day in the saddle..good eyes essential !

Contact Doug Braum <Doug.Braum at tgts.com>

what an amazing job!!