I bought a band pass filter as suggested and it did not help my problem. So today I returned to work after the President's Day holiday and took the filter with me. I through it on my Rhode & Schwartz FSP-38 Spectrum Analyzer I use in my lab. This spectrum analyzer also has a network Analyzer/Tracking Generator built in. I've used this in the past to calibrate my cables I use in RFI resolution and Spectrum Engineering testing of FAA equipment and filters.
The filter is: BPF-800-N and is tuned for 740 - 861 MHz.
Attached is the results of my testing. The insertion loss is between -4.25 dBm to 7.10 dBm. This what I would expect on a non-custom band pass filter. Just for comparison I spect'ed out a dual band pass filter several years ago for several tests I was asked to complete. This filter, costing about $900 each, covered both the L1 and L5 GPS band. The insertion loss across the operating band pass sections was no greater than -1.1 dBm. So you get what you can for the money you spend (
BPF-800N Band Pass Filter | Scanner Master), $79.00.
I have found though even the better and more expensive band pass filters exhibit will have anywhere from -2.0 dBm - 5.0 dBm so you can buy the best but you may trade off signal strength for the benefit band pass filtering.
Anyway tkae a look at the attached *.jpg file and enjoy.