15 Jan
2019
15 Jan
'19
4:13 p.m.
Tue 15-jan-2019
LimeSDR transmit check.
Fired up old HP 8614A signal generator at 1880 Mhz, and let it stabilize
for 1 hour.
Level measurement after adjusting ALC, 0dBm = -0.4 dBm as checked with
spectrum analyzer
Checked level with HP L423A probe.
Check of LimeSDR mini output.
Output as seen on spectrum analyzer -1.0 dBm. This correlates with
LMS7002 datasheet with
a possible 1 dB loss between chip and analyzer, including SMA-BNC coax
adapter, 2 m foam
insulated RG58 size cable, BNC - N connector.
So, for practical purposes the LimeSDR mini provides 0 dBm ( +/- 1.4 dBm )
LimeSDR receive check.
Receive antenna rigged with a 1/10 dB splitter, -10 dB port connected to
spectrum analyzer, -1 dB
port to LimeSDR.
Connect single Nokia Handset, and make a call from osmobsc to fixed
phone, so that only one mobile
is using TCH. Move phone to get different uplink levels and correlate
these to spectrum analyzer.
Since carrier is TDMA, use peak hold on analyzer.
Active subscriber connections:
conn ID=31, MSC=0, hodec2_fail=0, mgw_ep=rtpbridge/1@mgw
BTS 1, TRX 0, Timeslot 1, Lchan 0: Type TCH_F
Connection: 1, State: ESTABLISHED
BS Power: 10 dBm, MS Power: 10 dBm
Channel Mode / Codec: SPEECH_V1
No Subscriber
Bound IP: 192.168.1.75 Port 16384 RTP_TYPE2=0 CONN_ID=0
Conn. IP: 192.168.1.70 Port 4110 RTP_TYPE=3 SPEECH_MODE=0x00
Measurement Report:
Flags:
MS Timing Offset: 0
L1 MS Power: 10 dBm, Timing Advance: 4
RXL-FULL-dl: -51 dBm, RXL-SUB-dl: -51 dBm RXQ-FULL-dl: 0,
RXQ-SUB-dl: 0
RXL-FULL-ul: -54 dBm, RXL-SUB-ul: -54 dBm RXQ-FULL-ul: 0,
RXQ-SUB-ul: 0
Level on uplink -54 dBm, indicated on spectrum analyzer -53 (-63) dBm.
OsmoBSC# show conn
Active subscriber connections:
conn ID=31, MSC=0, hodec2_fail=0, mgw_ep=rtpbridge/1@mgw
BTS 1, TRX 0, Timeslot 1, Lchan 0: Type TCH_F
Connection: 1, State: ESTABLISHED
BS Power: 10 dBm, MS Power: 10 dBm
Channel Mode / Codec: SPEECH_V1
No Subscriber
Bound IP: 192.168.1.75 Port 16384 RTP_TYPE2=0 CONN_ID=0
Conn. IP: 192.168.1.70 Port 4110 RTP_TYPE=3 SPEECH_MODE=0x00
Measurement Report:
Flags:
MS Timing Offset: 0
L1 MS Power: 10 dBm, Timing Advance: 4
RXL-FULL-dl: -69 dBm, RXL-SUB-dl: -69 dBm RXQ-FULL-dl: 0,
RXQ-SUB-dl: 0
RXL-FULL-ul: -59 dBm, RXL-SUB-ul: -59 dBm RXQ-FULL-ul: 0,
RXQ-SUB-ul: 0
Mobile moved to another location within the lab.
Level on uplink -59 dBm, indicated on spectrum analyzer -60 (-70) dBm.
Conclusion:
For such a simple low cost SDR, the accuracy seems within a couple of
dB. Instruments used
were are not "professional grade", at least not w.r. 2019, but I
estimate I can measure
within +/- 2 dB or so with this crude config. Power output is 10 times
lower than I expected,
I was probably mislead by some review on the web, and had to go down to
the actual scematic
and datasheet to understand that the expected level should be around 0 dBm.
(thanks for pointing this out, Harald)
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.
Else, I am impressed, good value for a low price tag. I had expected far
worse than indicated accuracy.
Best Regards,
Gullik