logo
Most Viewed Last 7 Days
436MHz DATV Up-Converter (553)
MK808/PVRUSB2/DigiLite (238)
DVB-S USB rx (161)
10GHz EyalGal unit (140)
146MHz RD06+RD15 Amp (133)
Archive2 - DATV Transmitter (133)


Cluster Activity

Spots per uW band today:
UK spotter or spotted only.

Solar data:
SFI
78
A-Index
12
K-Index
3
Exp.K
0
Sunspots
22
Activity
eru
GMF
qui
Aurora?
no

My Weather

Date:23/09/17 Time:22:34
Temp:16C
Wind Speed:12.5mph
Wind Dir:180deg
Pressure:1017.69mB
Humidity:118%
Dew Point:19.6C
UKHASnet
Analogue vs Digital

Here are the results from a few tests I did in 2011

Here we have some tests done at 4Ms Digital vs analogue quality...

With 4Ms 1/2 i set the power level so i could access GB3KM with a small margin, i then switched over to Analogue and set the same power level as the digital was.

Here is the result:

Analogue



Digital 4Ms 1/2 with same power as Analogue




I also tested the difference in power level between a locked signal at 1/2 FEC and then 7/8 FEC, the result was ~4dB difference. According to the specifications for DVB-S the actual number is meant to be 4.4dB so that is close enough for me!



When going down to 1Ms at 1/2 the signal to noise will increase another 6dB compared with 4Ms 1/2, so if we drop the power from the above test by another 6dB on the analogue transmission we get this signal level at the repeater... quite weak, where as a 1Ms 1/2 digital signal would be in lock.

Analogue 6dB lower signal



It just shows how well the lower symbol rates can get through compared with analogue!

The digital receiver at GB3KM is a Comag SL-35, the analogue receiver is a Standard Continental with IF Bandwidth at 16MHz i believe.
Both are driven with ~35dB gain Bob Platts type preamp tuned for a center frequency of 1280MHz.











Last page added:16/08/17 15:45
M0DTS.co.uk