Old 6" Hyperlow frame I had laying around. I built this discontinued frame to test my home made crossfire RX antennas. I have tuned the antennas with an vector analyzer by starting out with a too long antenna and cutting it shorter little by little until it resonates at your desired frequency, 915Mhz in my case. If the antenna is well constructed, impedance and SWR will automatically be in the sweet spot. impedance and SWR of these antennas is perfect. SWR of 1.00 and impedance of 50.1ohm. It doesn't get better, plus the antenna is higher up above the quad where nothing blocks the signal. Interference from the quad is also much less. At 4.3Km out and RF power set to dynamic 500mW max, RF mode is still in 150kHz mode at 300% link quality and -78dbm at a altitude of 60m (tested in a low noise floor area).

For those who are interested, the feed line is a RG178 coax cable with IPX/U.FL connector already installed (see link in the parts list under "Misc Parts". Feed line can be as long as you want. The radiating elements are both 70mm long, which is the correct length for 915mhz and with some heat shrink on the radiating elements to stiffen everything up. Resonance frequency, SWR and impedance change if you put stuff over your antenna. This antenna has been tuned with the heat shrink already on, which is the correct way when tuning a antenna. The radiating elements of 868mhz antennas would be about 3mm longer. It's not that critical, RC remotes don't transmit strictly on one frequency anyway. A HAM radio antenna for instance works reasonably well over a entire band.

Step 1. for 915mhz antenna: Remove 70mm of the outer plastc insulation and metal shielding from the coax cable. Careful not to damage the inner signal wire and its insulation.

Step 2. Remove ~2mm of the outer plastc insulation only, that's where you will solder the 70mm ground wire to.

Step 3. Pre tin the 2mm of the exposed metal shielding of the coax cable and one end of the ground wire.

Step 4. Solder the ground wire to the 2mm exposed metal shielding of the coax cable in an ~120 degree angle.

Step 5. Use some heat shrink to stiffen the antennas up and done.