Potential consequences are reduced longevity of the airspy, but I don’t know in practice whether the increased current draw is likely to be a problem. I powered my lna with the airspy for several weeks without issue, but changed to an external bias t. Buying the bias t was cheaper than replacing the airspy.
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Thanks Caius, I’ve never used an external bias-t before, is there a particular one you would recommend? I was thinking about powering it from a USB port on the RPi
Thanks
I’m using that combination on one of my setups and have the gain down to 32.8 to get anywhere near the 5% strong signals threshold. That’s with an external antenna.
I am using one like this: https://www.ebay.co.uk/itm/10MHz-6-GHz-bias-tee-broadband-radio-frequency-microwave-coaxial-bias-tee-w1-/163413995723?_trksid=p2349624.m46890.l49286
I have it connected to the 5v GPIO pins on the pi for power, but you could use a usb plug to do the same thing. You’d just have to make the connection yourself.
I just exchanged it with my AirSquitter for testing. Installed is readsb provided by wiedehopfs script including tar1090, graphs was installed afterwards.
Connected is the Jetvision A3 antenna outdoor.
Gain set to 31.2 is still too high giving me 10% of strong messages.
A little more traffic requires the gain to be reduced again. now at 22 with the blue FA stick (done at 21:20)
Impressive…
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I would add that the cooling requirements increase with the extra load on the Bias-Tee. The LDO component used to provide the Bias-Tee is rated for 200mA but not the heat dissipation of the Mini.
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My test bed is currently powering the Uputronics using a free USB-slot of a Raspberry Pi4 while on the other port the blue FA stick is attached.
I tried it a while powering the Uputronics using a seperate power line, but no difference.
I will see which power the Airspy is using, maybe the USB power is an alternative
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The Uputronics preamps can work just fine on the Bias-Tee with the normal operating conditions. The same goes for the RTL-SDR blog ADSB filtered preamp with extra cooling.
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Many thanks for this info. What would you suggest for ‘extra cooling’ when using the RTL LNA … heatsink case with fan for the RPi?
Sorry…one further question. What would you suggest as an acceptable temperature for normal operating conditions if using the Airspy Mini powering the RTL triple filtered LNA?
Many thanks
I meant extra cooling for the SDR itself. A small heat sink would help.
For a permanent setup, the max temperature at the aluminium case shouldn’t exceed 40°C. The electronics can still survive at 85° but only for a short period.
Many thanks for your answers, that’s really helpful
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The airspy mini running at 20 MSPS with airspy_adsb … without extra cooling that exceeds 40 C easily and that’s with maybe 20 C ambient. Maybe my unit took a hit early on when i was using the biast with higher current draw … don’t think i had adequate cooling then.
I’ve never tested explicitely but i’d assume 20 MSPS uses more power than 12 MSPS?
Just made a quick check regarding the range.
Last week Friday, using the Air Squitter:
And last 24 hours, where i changed to FA stick with Uputronics at half of the time:
seem to be a slightly better range. Keep monitoring it.
The short range values changed significantly because of a different approach in EDDF.
Further gain reducement required to 20.7, messages > -3dBFS still higher than 5%
Testing ongoing
Peak messages not that far away from an AirSquitter/Radarcape (Screen taken from the Planefinder client) while having 70 aircraft (non-MLAT) on the screen
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The max official sample rate for the Mini (without problems) is 12 MSPS. Running at 20 MSPS is possible, but has its limitations in terms of spectral purity and thermal envelope.
That said, it seems that you should still improve the ventilation around the unit.
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Did that long ago … just thought it’s worth noting for the Airspy Mini and ADS-B.
While it might not be official spec … it’s easy to run it at 20 MSPS … with airspy_adsb being the official software 
It seems like your setup is limited by the noise figure. I believe you can get much better results with a few simple changes:
- Move the preamp near the antenna
- Use a high quality, low loss, short cable between the antenna and the preamp
- You can use a standard quality cable between the preamp and the bias-tee
- Use a splitter to compare the performance of the receivers. The loss in SNR is negligible after the preamp.
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In the case of the Mini, the reference frequency is 24 MHz. To get 12MSPS, it’s a simple binary counter, but for 20MSPS, a whole PLL is run at a few hundreds of MHz, followed by many clock dividers. This adds noise and adds a few milliamps of current drain. The data throughput is also something to consider. More data means everything runs at a higher speed: ADC, DMA, USB transceiver, interrupts, etc. This all translates in more current and a higher thermal envelope.
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I’ve added some remarks in the airspy-conf configuration file.
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