Can anyone figure this out?

[zeppelin11]

Finally upgraded from an old analog to a Uniden BCD436HP scanner a few months ago. I was using a software based scanner and ordered the RTL-SDR which came with their antenna and i decided to switch out my old make shift antenna with their antenna and raised it 40' up a tree and it works great for my local 150mhz bands. This antenna as well as my RG8 cable approximant length 50-60' does not meet any requirements for a p25 system 800mhz but i keep a p25 system active in the database anyways. I'm 2 counties away however one night i all of a sudden started pulling in this p25 system and was receiving up to 3 bars of signal but it lasted maybe 30 minutes it left as quick as it came and i haven't heard it since. Does anyone have a theory as to how and why this could of happened considering my setup? I'm Approximately 25 miles away from the county line. I have also posted a link below to the RTL antenna. Thanks for any and all feedback!

Amazon.com: RTL-SDR Blog V3 R820T2 RTL2832U 1PPM TCXO HF Bias Tee SMA Software Defined Radio with Dipole Antenna Kit: Electronics

Buy RTL-SDR Blog V3 R820T2 RTL2832U 1PPM TCXO HF Bias Tee SMA Software Defined Radio with Dipole Antenna Kit: Radio Antennas - Amazon.com ✓ FREE DELIVERY possible on eligible purchases

www.amazon.com

 

[spanky15805]

Humidity and temperature differences in your neck of the woods are creating "ducting", especially siting on the Gulf coast. Just wait for a huge winter cold front to hit your area, 250 miles might be achievable.

 

[zeppelin11]

Just read up on Tropospheric ducting. I kinda figured it had something to do with the weather i also looked back at that night's weather forecast and conditions were perfect. Thank you for pointing me in that direction!

 

[mitbr]

To the OP this website might be helpful it shows real time vhf tropo on a map....

VHF Propagation Map

aprs.mennolink.org

Tim