I ordered 2 units with my own $ from heli-nation. Non-affiliate link to the item here: TBS 1.2GHz VRX Notch Filter (868/915 MHz).
For reference:
Marker 1; 900 MHz
Marker 2; 930 MHz
Marker 3; 1258 MHz
Marker 4; 1280 MHz
Trace 1 and 2 measure the thru response (S21, S12)
Trace 3 and 4 measure the SWR (S11, S22)
Filter #2:
Both filters cascaded in series:
Results:
- The shape of the rejection notch is is very much centered around 915 MHz.
- There may be a different SKU for our European friends, but as it stands there's only about 17 dB of rejection at 870. This may or may not be enough depending on the filtering performance an blocking performance of your video receiver
- The part to part variation appears to be pretty low for the 2 samples I purchased (as expected since it's a pcb based design)
- Cascaded (2 devices in series) insertion loss of 1.2 dB @ 1280 MHz is impressive for the 50 dB + of rejection in the 900 MHz band.
Thoughts:
The single stage: Reasonable rejection of >= 25 dB in the US ISM band. This may be enough for general rejection of crossfire signals at a flying field. But might not be enough if you flying down to sensitivity doing long range flights. Especially if you are only a few feet from your groundstation or using the fatshark goggle modules. More on this in part 2.
The cascaded filter: I would hazard to say the it would def be worthwhile for Alex to spin a separate version of this with the two filters in series on one PCB. The insertion loss in the passband is very good for the amount of rejection it gets at 915. With a slight re-tune to shift the passband down just a touch for lower loss at 1258 and an LNA on the front end to help improve the overall noise figure of our receivers, you'd have a killer front end setup for both around the park and long range flying.
Coming in part #2:
Shootout with various receivers to measure actual
Hope you enjoyed this. As they say on youtube. stay tuned for part 2...
Keep up the good work
ReplyDeleteWow really cool test
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