Old Koreelah Posted August 23, 2015 Share Posted August 23, 2015 Maybe someone can help me. My hand-held Vertex is connected to a dipole aerial set about 60 degrees off vertical, mounted behind me on the right-hand side inside the plywood fuselage (no Don, it's not made of papier mâche!). People sometimes report my radio transmissions are weak or broken. Having spent money fixing all aerial connector faults, my next step is to fly a test pattern and have someone on the ground report on my transmissions, to see if there is a significant variation in signal strength to the sides rear and front. That test would require a mate to report back. (Since SDQDI reckons I haven't got any mates, I'll ask the forum!). From in front most of the aerial is blanketed by my body and the engine. How much impact would this have on signal strength? Link to comment Share on other sites More sharing options...
Guest asmol Posted August 24, 2015 Share Posted August 24, 2015 I remember a talk at our airport about a year ago regarding radios. Firstly, you are probably breaking the rules by using this radio airborne with the exception of an emergency. They are not approved for use in an aircraft but are limited to being a handheld device used only on the ground. That being said and from what I remember a lot of your signal will simply be absorbed by your body and the engine etc. when you are flying directly to a source because you have the aerial mounted in the fuselage and a heap of stuff in between you and the receiving station. It makes common sense when you think about it. I also remember something about the antenna had to be at least 600 mm away from you physically otherwise it could do damage to your body and basically cook you with RF although I doubt and handheld has anywhere near these problems when compared to a proper radio because you are using a handheld in front of your face usually when you are talking into it and it doesn't give you brain problems and send your eyes all funny. Link to comment Share on other sites More sharing options...
cscotthendry Posted August 24, 2015 Share Posted August 24, 2015 If it's a handheld radio, maybe also check the state of the battery. Also, how are you communicating with the radio? If you have a headset plugged in, does the radio have a mic gain setting? If there's not enough audio drive from the mic, the modulation level on transmit could be insufficient. If you're just speaking into the speaker as you would use a handheld on the ground, the voice input may be insufficient to overcome the cockpit noise in your transmissions. Does your aircraft have a metal frame? You are correct in assuming that any metal between the antenna and whoever is receiving your transmission will affect the signal strength at the receiving end, but I think more likely is lack of modulation of the output rather than the received signal strength. Link to comment Share on other sites More sharing options...
Nobody Posted August 24, 2015 Share Posted August 24, 2015 I remember a talk at our airport about a year ago regarding radios.Firstly, you are probably breaking the rules by using this radio airborne with the exception of an emergency. They are not approved for use in an aircraft but are limited to being a handheld device used only on the ground. Asmol, refer to Section 1.5 of AIP GEN 1.5. Hand held radios are allowed for aircraft 600kg MTOW weight and under in class G airspace. Old Koreelah, Is the antenna tuned for the aviation frequencies ? You state that you have a dipole antenna mounted 60 degree off vertical. A dipole tends to be fairly directional is mounting it vertically the best orientation? Link to comment Share on other sites More sharing options...
Robbo Posted August 24, 2015 Share Posted August 24, 2015 In my former life I was an avionics tech, you will find that the radio could be transmitting at a lower power, may sound stupid but check the settings in the radio and see if it is set on low power as most have high/low power settings. The radio may also require a tuneup, a bit of tweaking in the radio can fix problems like this. But its hard to say without seeing the unit so I suggest taking it to the local avionics tech. 1 Link to comment Share on other sites More sharing options...
SDQDI Posted August 24, 2015 Share Posted August 24, 2015 So the nickname ' the flying piñata' isn't technically correct?! But thinking back, on Saturday you were in front of us and heading towards tamworth and I could hear your transmissions (albeit a bit weak) when the tower couldn't. I guess, just because I'm such a nice fella, I could help you with your testing one of these days. Maybe I could just fly circuits and have you go out and back. Sorry this post got delayed, it was meant to be straight after old Ks but I got sidetracked. 1 Link to comment Share on other sites More sharing options...
Old Koreelah Posted August 24, 2015 Author Share Posted August 24, 2015 Thanks for the replies fellas. Most of the info given went straight over my head; I'm not stupid (stop it SD) but electronics and formulas make my eyes glaze over. Scott -the aircraft is all wood with fabric skin (but remember the fabric is sprayed with a thin layer of aluminium to block UV). I use the remote mic on my DC headset and yes, there is a fair bit of cabin noise so I sometimes have to throttle back when transmitting. Nobody -the antenna was supplied by SMC, along with a Black Widow TT2000 extension cable designed for aircraft radio band. I was advised to install the dipole vertically, but it doesn't fit, so it's mounted at an angle. Having read the links sent, it seems I might be best off to mount it horizontally. It will fit in one wing leading edge (I can slip it in past the ribs) or inside the tailplane. Link to comment Share on other sites More sharing options...
Oscar Posted August 24, 2015 Share Posted August 24, 2015 OK, I'm no expert here, but I think a dipole should be mounted vertically. As I THINK I understand it, the propagation pattern is something of a 'figure-8' cone pair, aligned with the halves of the aerial.. The bottom half of the dipole is the effective ground plane. Later Jabs. have a dipole mounted on the fin spar web - simple equal lengths of 12mm wide x 2mm thick aluminium strip, from memory, 482mm long ( I can measure the length of each half if it is of use to you). A suitable bit of aluminium strip is about $12 from an aluminium supply shop - even Bunnings (gag) may have it. I suspect that a purely horizontal dipole orientation may cause a 'hole' in your coms when pointed at the tower.. or in the circuit when aligned with other aircraft. (though vertical will do the same for other aircraft in the circuit at the same or near height.) I believe the Jab set-up is reasonably ok for all normal use. And yes - I rather suspect the aluminium UV layer for your fabric may be setting up a Faraday cage - why don't you check with Dafydd about that? As you know, he's been fa#ting around with fabric on his Blanik. 1 Link to comment Share on other sites More sharing options...
Old Koreelah Posted August 24, 2015 Author Share Posted August 24, 2015 ... A suitable bit of aluminium strip is about $12 from an aluminium supply shop - even Bunnings (gag) may have it.... Thanks Oscar, I appreciate you having to do unpalatable things like even mention Bunnings-grade aluminium. Fear not, for my little beast has shopped at the Green Shop with the Hammer. It uses a few bits of their extrusions in non-critical areas. ...I suspect that a purely horizontal dipole orientation may cause a 'hole' in your coms when pointed at the tower.. or in the circuit when aligned with other aircraft... You're probably right Oscar. On Saturday Tamworth tower couldn't read me clearly as I was head-on (shielded by my body and the engine) but said I was clear after I turned downwind- transmitting thru the side plywood. ...And yes - I rather suspect the aluminium UV layer for your fabric may be setting up a Faraday cage - why don't you check with Dafydd about that? As you know, he's been fa#ting around with fabric on his Blanik. I'll do that; I hope to call in to see progress on his test cell in late September when I'm up that way. 1 Link to comment Share on other sites More sharing options...
turboplanner Posted August 24, 2015 Share Posted August 24, 2015 Thanks for the replies fellas.the aircraft is all wood with fabric skin .....the club lounge method. Link to comment Share on other sites More sharing options...
Oscar Posted August 24, 2015 Share Posted August 24, 2015 OK - take some earmuffs - it is planned that the thing will be well and truly running for real by then. The huge spanner in the works dropped by CASA has been /is about to be finally overcome, and testing should be going apace, to get it done before the ambient temps get so high it becomes unviable (at least during the day). 1 Link to comment Share on other sites More sharing options...
Cosmick Posted August 25, 2015 Share Posted August 25, 2015 A verticle mount can be upside down. Mount the aerial under the aircraft. The times you transmit to someone well above and in front will be limited. 1 Link to comment Share on other sites More sharing options...
SDQDI Posted August 25, 2015 Share Posted August 25, 2015 I agree Cosmick, BUT I have mine mounted on top of the fuse as when mounted underneath there is a very real possibility of 'rubbing' the aerial off on long grass ect. My transponder aerial is mounted under my fuse not to far behind my undercarriage and I have managed to wipe it off when landing in a higher than last week crop:wink:. I replaced it and am more mindful of it but I don't like the idea of risking my radio aerial down there. Link to comment Share on other sites More sharing options...
Kyle Communications Posted August 25, 2015 Share Posted August 25, 2015 Asmol, refer to Section 1.5 of AIP GEN 1.5. Hand held radios are allowed for aircraft 600kg MTOW weight and under in class G airspace.Old Koreelah, Is the antenna tuned for the aviation frequencies ? You state that you have a dipole antenna mounted 60 degree off vertical. A dipole tends to be fairly directional is mounting it vertically the best orientation? Nobody you didnt actually read what he said.....the radios are NOT type approved for airborn operation especially the Vertex. Also I dont think any of the Icoms are approved either at the moment. They are all approved for ground only ops 1 Link to comment Share on other sites More sharing options...
Kyle Communications Posted August 25, 2015 Share Posted August 25, 2015 I agree Cosmick, BUT I have mine mounted on top of the fuse as when mounted underneath there is a very real possibility of 'rubbing' the aerial off on long grass ect.My transponder aerial is mounted under my fuse not to far behind my undercarriage and I have managed to wipe it off when landing in a higher than last week crop:wink:. I replaced it and am more mindful of it but I don't like the idea of risking my radio aerial down there. My noseleg broke off and smacked the nose down and broke the prop and bent the floor....my Comant antenna which is under the front up near the firewall copped the brunt of it and its fine..infact it is still the same one. The best place for antennas in our type of aircraft is underneath not on top of the fuselage. My airband and UHF CB antennas are underneath the APRS is on top....only because I cant fit any more underneath Mark Link to comment Share on other sites More sharing options...
Yenn Posted August 25, 2015 Share Posted August 25, 2015 I have a fabric fuse with an internal antenna, also a Vertex radio. No problems, so I don't think the aluminium in the paint should be a problem. How does the Vertex go using the little aerial it would have come with. My antenna is not a dipole, but a vertical whip with a cross od copper metal about 12mm wide by 800mm long under it as a ground plane. 1 Link to comment Share on other sites More sharing options...
Old Koreelah Posted August 25, 2015 Author Share Posted August 25, 2015 Thanks for all the posts and PMs, people. I have doubled what I know about radios. Looks like the short-term plan is to grovel inside the fuselage with a measuring tape. It might be possible to mount my current dipole antenna vertically if I drill a hole and poke it up thru my rear locker. If that isn't possible I might try installing a Morris Loop. Thanks for your suggestions. Link to comment Share on other sites More sharing options...
Roscoe Posted August 26, 2015 Share Posted August 26, 2015 Nobody you didnt actually read what he said.....the radios are NOT type approved for airborn operation especially the Vertex. Also I dont think any of the Icoms are approved either at the moment. They are all approved for ground only ops I thought the Icom A-15 was approved for all ops? Link to comment Share on other sites More sharing options...
Old Koreelah Posted September 7, 2015 Author Share Posted September 7, 2015 Report time: I ended up mounting the existing dipole aerial vertically, which required it to stick out the top of the fuselage. Added a bit of streamlining. After major surgery to the carrier to clear the aerial I still managed to catch it when rotating the gantry. Damn dipole broke, so I cut up an old 27meg whip to serve as a splint. It seemed to work well on the trip to Narromine. 4 Link to comment Share on other sites More sharing options...
Oscar Posted September 8, 2015 Share Posted September 8, 2015 Jeez, she looks a picture. If I patted her on the nose, would she follow me home? 1 1 Link to comment Share on other sites More sharing options...
Old Koreelah Posted September 8, 2015 Author Share Posted September 8, 2015 Jeez, she looks a picture. If I patted her on the nose, would she follow me home? Wait till the prop stops! Link to comment Share on other sites More sharing options...
Oscar Posted September 8, 2015 Share Posted September 8, 2015 Nah, I like a girl with Spirit.... Wing fences and vg's..... you've been fettling, haven't you? Link to comment Share on other sites More sharing options...
Old Koreelah Posted September 8, 2015 Author Share Posted September 8, 2015 Just trying to get the lowest possible safe landing speed. (Jodel purists would not approve: all my mods added weight and increased stall speed.) 1 Link to comment Share on other sites More sharing options...
Oscar Posted September 8, 2015 Share Posted September 8, 2015 There can be a significant difference between 'safe landing speed' - one at which a wee hiccup results in no more than a bit of a soggy, recoverable, embarrassing wallow - and a slower but vicious stall break that is unrecoverable by human intervention in less than 45-degrees plus of wing drop. I'll personally take the extra 20 metres of landing run from the former EVERY time to chancing the latter. 1 Link to comment Share on other sites More sharing options...
Old Koreelah Posted September 8, 2015 Author Share Posted September 8, 2015 The Jodel's tapering wing is quite efficient but mine had a nasty wing drop last time I did stall tests. Hence the relocated VGs and fences. Next opportunity I'll do some experimenting with the location of Dafydd's stall strips, which he predicts (in addition to limiting how far the elevator pushes the tail down) should set up a reverse vortex strong enough to block the stall from propagating out along the wing. 1 Link to comment Share on other sites More sharing options...
Recommended Posts
Create an account or sign in to comment
You need to be a member in order to leave a comment
Create an account
Sign up for a new account in our community. It's easy!
Register a new accountSign in
Already have an account? Sign in here.
Sign In Now