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Author Topic: cheap amazon BCB AM filter....  (Read 663 times)

Offline IQ_imbalance

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cheap amazon BCB AM filter....
« on: December 14, 2017, 0203 UTC »
Just received my cheapo Chinese BCB AM filter from Amazon.  The good news...it doesn't make the radio (Afedri SDR-net) deaf.  The bad news...it doesn't completely deal with my intermod problem.  I'm just going by eyeball right now, i'll try and do some direct comparisons +/- filter later this week or weekend and post some data.  I do wonder if it would be possible to stick it between the antenna probe and the amplifier on my H800, however....logically it seems to me at least it would make sense to remove as much unwanted signal before the amp......
LOG/NE-SW unterminated BOG
AFEDRI SDR-Net
Central MD

Offline Josh

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Re: cheap amazon BCB AM filter....
« Reply #1 on: December 14, 2017, 1839 UTC »
I agree, filtration before amplification will do wonders for signal purity and dynamic range. Also make sure you're not too high in front end gain in the sdr as well as having the noise blanker set too sensitive.
Conveniently located near Vincennes Indiana.

Offline IQ_imbalance

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Re: cheap amazon BCB AM filter....
« Reply #2 on: December 16, 2017, 2113 UTC »
OK here's the clean +/- comparison i promised.  No smoothing or noise reduction and all the auto-adjustments on the waterfall turned off.  The top panel is filter in-line between the H800 and the Afedri, the middle panel is with the filter removed, and the bottom panel is the filter put back.  The strong signal you see is 930 kHz.  Not shown is the trace on the S-meter; baseline noise went from S2 with the filter on to S5-6 with it off. 

So...for $20 bucks you can get some BCB relief.  Does it solve all my intermod problems?  No...perhaps in part because the BCB filter is working on the amplified signal from the antenna.  Turns out the H800 has the preamp IN the antenna probe, and the little box is just the power supply for that. 

Next step is to lay out my LOG and try that +/- the filter.
LOG/NE-SW unterminated BOG
AFEDRI SDR-Net
Central MD