Re: Best Gain Settings for 137 mhz reception
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"Free" gain setting allows the user to set the RF, IF, and mixer gains independently.
I am now on my third AirSpy. The first two, AirSpy Ones, are laid to ruin by close-by lightning strikes (front end damage and USB loss). So far...... ALL have (and do) need an FM Stopband filter before feeding RF to the input SMA connector. The strongest FM signal here at my location is -35 dBm on the antenna I use for 20.1 MHz solar and Jupiter emissions. That isn't 'too' strong as signals go, but its enough with the other stations in the FM band, all less than -35 dBm, to cause several intermod products to show up in a frequency slice from 18 through 26 MHz from the AirSpy. The filter I use is -40 dB throughout the FM band. With that, I have no problems with FM broadcast.
Here is another solution from AirSpy.US:
These preamps are filtered for the band of interest and will reduce the problem with the FM BC band while still giving you better S/N (nower NF). From my measurements, the AirSpy typically runs with a NF around 4 to 5 dB. They claim better with the versioin 2, but I have not measured mine. The NF is also pretty constant over the advertised frequency range. This is more than adequate for HF, but at and above 50 MHz, you can gain better S/N by using a filtered, 'reasonable' gain preamp. Spend the $53 from AirSpy America and cure all your problems. Personally, I'd design and build what I need, but not everyone has the test equipment to assure what they build is what was intended in the final product.
BTW: The FM SBF filters from Amazon have a rather marginal track record. Some work, others don't, loose components, bad solder - typical Chinese start-ups.
Dave - WØLEV
On Sat, Sep 9, 2017 at 1:40 PM, doug <dmcgarrett@...> wrote:
Dave - WØLEVJust Let Darwin Work