Hello Harald et.al.
On 2019-01-17 23:18, Harald Welte wrote:
Hi Gullik,
thanks a lot for your extensive measurement and testing, as well as the report here to this list.
On Tue, Jan 15, 2019 at 04:13:29PM +0100, Gullik Webjorn wrote:
So, for practical purposes the LimeSDR mini provides 0 dBm ( +/- 1.4 dBm )
Yes, that's more in-line with what I remember. Depending on unit and frequency, I think the expected level is roughly between 0 and 4 dBm.
Level on uplink -54 dBm, indicated on spectrum analyzer -53 (-63) dBm.
So you're saying that the level displayed in the 'show lchan' actually was almost exactly the measrued level (-53 dBm)? That's a very big surprise to me. As far as I understand, the LimeSuite API never reports any absolute values, but rather only in dBFS (dB to full scale). So it's a bit of a mystery how you can get such an accurate reading?
Yes, I am surprised myself, but I documented what I saw. Note also I checked at two different levels. I will probably redo these tests as I get a more output and a "better test range".
For practical use outside a lab output is far too low. My plan is to add a small simple booster to bring level up to +15 which would allow me to cover my 2 acre lot without breaking any rules.
We made some osmo-bts-amp / osmo-bts-pa designs and devices some time ago, but they only have 10dB gain. They were made to go from +23 to +33 dBm, and not for such low input signals, where higher gain stages are required.
Make surey you carefully look at your spectrum and use transmit filters to suppress the harmonics that your PA will be generating.
Yes, currently I use a linear amp designed as a preamp, but output level is a bit below 1 dB compression point, so we are operating linear, current output is 8-9 dBm, which enables extending the test range. I am limited to 100 mW indoor, +20 dBm.
Else, I am impressed, good value for a low price tag. I had expected far worse than indicated accuracy.
Regards, Harald