I wanted to do long range telemetry so I got myself a dipole antenna for the modem.
I never could check the range because the plane couldn't get a gps lock anymore, with the modem powered on. With the modem powered off, I had a 3D GPS lock, 17 sats in seconds.
What can I do to get both long range telemetry and good GPS?
Can you add a picture of your hb antenna? Or a link to the tutorial on how to make it? And a parts list?
I was thinking of DIY 4 elements yagi antenna for the GCS. Would that work?
Did you ever fly beyond 20 km?
The hb antenna is basically the coax from which I removed the shielding for L/4 165mm (so 300/433/4*.95), at the point where the shielding stops a soldered a wire of the same length. The antenna is taped on the tail of the plane and vertical polarized.
My TX/RX is not shielded and close to the GPS receiver, the antenna feed coax runs over the GPS receiver. I did not experienced any drawback in GPS performance. On the picture with the RX/TX you can see the ferrites around the coax feed and signal wires.
Yes you can use a 4el Yagi, but you have to point it towards your plane, my Diamond X5000 antenna has full round radiation pattern in a shape of a "pancake" with 8dBi gain. So my antenna is fixed at the roof of my house. Height of he antenna is key!!!
After several long distance experiments my main conclusions where: Avoid man made disturbance (select empty frequency), Antenna height, Plane antenna far from other electronics.
No beyond 20Km I did not go, the "distanceRSSIremain" showed over 100Km reserve, but I doubt if the rounding of the earth is taken in account .
I'm currently experimenting with a video camera in the plane and a FM link at 1296MHz, also here my goal is 20Km, but here I use an rotated 55el vertical Yagi at 20m height. This test is not finished due lack of time and good weather.
I don't post often but have been a member here for many years. Please take the time to consider the advice of Gisela and Joe. I have never directly needed their advice but have a great respect for their methodical problem solving skills. I have however been an engineer for 39 years and their method is a tried and tested one.
OK I solved it! Thanks everyone - and especially Joe - for your suggestions. Powering the modem via a separate UBEC - like Joe suggested - worked like magic. No balun needed, no ferrite core.
The modem came with a little 4 wire cable that became a 6 wire plug at the autopilot side. I removed the red wire from that socket by lifting the little plastic finger keeping it in place. I then soldered a hitec female connector to the red wire. Next I cut the black wire and made three way junction, one continuing to the autopilot, the other to hitec. My UBEC had a hitec male connector. I forgot to add the ferrite core again, but it worked so I didn't bother.
I suppose moving the dipole to the tail and making it a half wavelength dipole would be even better, I could then move the GPS & Rx to the front. But I didn't have the right cables and mounting surfaces to do that. And this just worked.
Here's an update overview of my tries. If you have more questions, just ask!