Let’s see if I can keep the numbers straight here…
In a perfect world (and antenna manufacturing),
1090 mhz vertical antenna lengths:
Full wavelength: 10 5/16ths Inches or 0.262 meters
5/8ths wavelength (very common): 6 15/32nds inches or 0.164 meters
1/2 wavelength: 5 5/32nds inches or 0.131 meters
1/4 wavelength: 2 19/32nds inches or 0.065 meters
A dipole antenna is typically 1/2 wave length each side (each element being 1/4 wavelength)
By the math (and some great websites that do it for you), your 66 cm antenna is MOST LIKELY either a 2 meter or 440 mhz type antenna. Depending on how I break it down (1/4, 1/2 wave) I come up with 170mhz through 849 mhz
22 Cm is ~ 8.66 inches
at a 1/2 wave dipole antenna (4.33 each leg), it’s tuned for 1296 mhz, which would explain why you’re getting such better results.
Antenna’s receive and transmit off the sides, not the top straight up or out the bottom. Without getting into a long antenna theory discussion, yes you can make an antenna transmit/receive out the end, but not typically for a ‘wire’ antenna, and there is the ‘polarization’ of the ‘antenna receiver to transmitter’ to factor in. Aircraft have vertical polarization, which is why our antennas go up and down. If you lay it on the side, it’s horizontal polarization. WILL one receive the other, MOST the time but it’s VERY specific and usually not very good. (If I’m remembering all my past reading correctly that is, someone feel free to correct if I’m wrong).
I set up my PiAware a week ago. I took a Pi out of my cabinet, downloaded the image to an SD card, hooked up my RTL-SDR receiver I had in the same cabinet, Looked up what the length of a vertical antenna should be for 5/8ths wave, went to my shed, found an old piece of CATV hard line (the kind that runs on the poles down the street), sliced the aluminum shielding into 3rds, cut it to the correct length, it already had an N connector on it, so I put an adapter on it to go from N to SO239 connector on it, and screwed a piece of coax I had laying around to that and put a SMA adapter on the end to connect to the RTL-SDR and VIOLA! I’m picking up aircraft like crazy.
Do a search for ANTENNA LENGTH CALCULATOR, figure out how long you want your antenna to be (Full, 5/8, 1/2 or 1/4 wavelength, FULL or 5/8 is what I recommend), then get a piece of coax, measure the length on one end, carefully remove the covering, spread the shielding wire (outer wire) apart down at the bottom of your measurement and pull the center conductor through that, twist the shield together , and BOOM, you now have a dipole antenna. Hook it up (TV coax is an F connector, CB/Amateur Radio TENDS to use PL259 connectors for VHF/HF, some use N connectors) with an adapter to the SMA connection and see how well it works… You’ll probably be pleasantly surprised.
There are designs out there I’ve seen that make a vertical antenna for this using a soft drink can for the ground plane (part that connects to the shield), or things like that, and some simply had a piece of wire stuck in an adapter for the center element (CANTENNA’s for ADS-B would be your search).
If you know any amateur radio operators who might have an antenna analyzer, they might be able to check your antenna’s and tell you exactly what freq they are designed for… Antenna lengths without a tuner are very critical when transmitting, but can have a large impact on receiving as well.
Best of luck!
Gary