I’m in an area close to (and line of sight to) several 4G masts and have a high 800MHz signal level here. I thought a filter and/or LNA might help. I’m using in indoor 1/4 wave spider.
These just arrived from ebay, which I think I’ve seen pictured here before:
My message rate was around 250/s. Adding the filter alone dropped that to 60/s. It only took a moment to add it in. Removing the filter immediately raised messages to 250/s again.
Next I added in the filter followed (on the receiver side) by the LNA. I got about 150/s messages. Remove both and back to 250/s.
With the LNA alone, I got about 120/s. Again, remove and messages go right back up to 250/s.
All of that was done quite quickly, while I had a fairly constant message rate. I’m a bit surprised at the results. I really thought the filter would make a positive difference, given the proximity of 800MHz towers. I certainly didn’t expect such a huge drop.
I’m going to continue experimenting, and I’ll connect my RSP1A to the antenna and try to get some meaningful numbers. (so there’ll be no FA feed from me for a while when I do that).
Any thoughts or suggestions would be welcome. I’m effectively new to RF as well as ADS-B tracking, despite having a full amateur license gained decades ago. It, and my once-held knowledge, has been unused for most of that time because I got distracted by computers.
I’m using a cheap RTL dongle on my Pi for PiAware. I’m also surrounded by hills slightly higher than me. I’m on the side of one of them, facing into the broad valley, at a good height but not quite at the top.
I made a basic 1/4 wave antenna with four 45° radials from a length of 1cm thick 75Ω coax, by just stripping it down to expose the centre and poking the radials into the screen between the dielectric and outer. It works well, better than my first cantenna, especially when I put it about a foot above a metal plate. That increased my message rate by 20% instantly. I guess it moved the radiation/gain pattern a bit higher, where it’s useful to me over the hills. I know I have some impedance mismatches in the system. My dongle has a 75Ω input but the cables are 50Ω. I’ll deal with that some time but I don’t think it’s a huge issue.