Timz Corepeater MeshCore Repeater
Bandpass Filters
If you looked at my SCANS page. you will see that my MeshCore repeater had poor receive; due to adjacent channel interference caused by a nearby cell tower. The noise floor was in the mid -70's to the low -80's
There are many of these bandpass filters available, but a lot of them are for RFID and other low power applications, and the rated max power handling for the bulk of them is 100mw to 200mw. The two filters shown below claim to handle 1w tx power.
Filter #1; purchased from eBay for $24 (make certain to select the correct frequency band when ordering). I order a second one, this time from Amazon. Once received (24 hours later) I swept it, identical to the eBay offering.
this one claims to handle up to 1w TX, and I measured a 1.5db loss through it @ 910mhz. Here is a sweep of it:
I installed this filter inline to the antenna:
and it made a noticeable improvement. The "Two Way" numbers almost doubled, and the noise floor fell considerably. I went from a noise floor in the upper -70's to the lower -80's... to noise floors in the mid -90's and low -100's.
Early on (pre-filter) I had to disable the Heltec V4.2 LNA set radio.rxgain off due to the terrible noise floor ... things did improve a little bit turning the LNA off. After installing this filter, I monitored it for about 10 days... noting the improvement... and then I re-enabled the LNA. The repeaters receive greatly improved even more... and the pleasing mid -90's and low -100's noise floor did not degrade any. I was able to get the benefit of the built in LNA after filtering out all the adjacent channel signals.
Filter #2; Purchased from LINK for $48 (make certain to select the correct frequency band when ordering):
My sweep matched this one I found online. The attenuation on the sides is not as steep as the first filter, and I found 3.4db insertion loss @ 910mhz; double the loss as the first filter. I never connected this filter into the system, the tests were too disappointing.
