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| So I've been building an ultralight |
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| danny_galaga:
Update part 1: So my radio isn't brilliant. And I'm not very methodical when it comes to trouble shooting. But what I have noticed is the signal seems a lot clearer when I'm turning to base. I didn't know what to make of that until I realised the signal doesn't seem as good on climb. It finally occurred to me what might be happening the other day so I took some measurements today. I have a dipole antenna. When I installed it I felt quite chuffed because it seemed kinda vertical and was a tidy install. Dipole is simple but due to the length is a bit tricky to find somewhere near vertical, else you have to bend it. But how close to vertical is my installation really? I imagined it was something like 60-70°. But that was an optical illusion due to me being distracted by the door frame. See attached pic. In fact, when taxiing, it's about 45° 😲. So this is my rough estimate of angles: Taxi: 45° Straight and level: 50° Descending on final: 55° Climb: 40° ! The question I guess is this: I think I have more than one problem with my radio, but given the variation in quality of signal seems to be related to aircraft attitude, and looking at the general angle mine is at, will I at least reduce or eliminate one problem by making my antenna vertical? My solution would be to move the base of it (bottom right in that first pic) about 400-500mm back so it doesn't end up running against the aluminium upright when I straighten it up, and poke the aerial through the top of the fuselage. This crossed my mind when I was first installing it but I opted for the simplest solution knowing I could try something else later. Dipole aerial is on the other side of that wooden strip. |
| danny_galaga:
Update part 2: I figured it couldn't hurt to move it. Only thing of course is because of the length, unless it's in the tailplane, something's gonna poke out. So 3D printer to the rescue 😀 There wasn't a lot of traffic this morning. I did a circuit without no one else on the radio. From that brief flight it seems that making the aerial vertical has made it sound (to me) more consistent. That is, whether I was on the ground, or downwind or turning to base it sounded much the same . It was getting a bit breezy for this low hours pilot so I took the opportunity to work on tidying it up. I was hopeful that someone might be on the radio down the other end of the airstrip and I wanted to test the difference from port and starboard 'broadside'. You'll notice because the aerial is close to starboard, it's closer to some tubes. My general understanding is the dipole radiation pattern is two torus. Basically two doughnuts with a very small hole. I have one tube crossing the aerial virtually in the centre where the two 'doughnuts' are 'stacked', so I figure it won't have much effect. The top tube will have more of an effect. As you can imagine, the number of degrees of 'shadow' it would cause depends on its diameter and the distance from the aerial. This is pretty close. So I would say maybe 40mm of the aerial just there is 'shaded' by about 35°. It gets too complicated to imagine how much effect that is though, because the rest of the aerial around it must radiate some energy into that space. As well, I believe a metal object close and in the way will re-radiate some of the energy, thus 'filling in some of blanks' so to speak. The signal won't be as good in that general arc but more than zero. ANYWAY, with all that in mind, I taxied the plane to have the starboard side perpendicular to the runway so that if there was someone down the other end, my signal should be somewhat shielded by that tube. Someone was down the other end. They read me 4/5. I then turned around 180°. They read me 5/5. This all adds up. So, in the end it would seem it was worth fiddling with the aerial. On the ground, slightly weaker signal on the starboard side, but still readable. In the air, for most circumstances it should be fine above, below and behind. I feel for any installation the engine in front will cause some shadowing. And starboard, from a distance should be fine as the radiation 'normalises'. Close, the total of the signal will be stronger so I imagine still readable. Probably would be better to have it in the centre, but I would probably have to run a new cable to reach. This was much easier 😄 |
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