Thursday, March 22, 2007

More sdr-IQ tests

Tests at sunrise
I did some more tests with sdr-iq vs sdr-14 vs Icom-9000. One thing was a simultaneous listening "by ear" when some NA stations were disapperaing about an hour after the local sunrise on March 22. As you can see on the picture the stations (CKEC on its split 1320.008 and other) are very weak at about -100 dBm (SpectraVue s scale). That means you can hear some muisc or talks but can not understand speaking. I compared the three receivers using same antennas, either a KAZ (at 340 degr.), 10x40 meters or a longwire of 150 meters (at 340 degrees). A preamp. of 10 dB was used and there was no problem now when the RF levels were low (I tried both sdrs at 0 dB RF or -10 dB RF gain). My Icom9000 is not the best receiver as far as sensitivity is concerned, but it is "good enaugh" on SSB (under 1 uV, on AM about 1 uV). I found that the reception on MW was rather equal, but the SDRs were at least as good as the Icom. There was no need for notch & PBT however. On SW I tried to listen to barely audible Peruvian on 4790.1 where I "think" the sdr-14 had best signal after Icom and sdr-iq. Alltogether the differences were marginal.

Speaking of Dymanics
You have to note however, that the low dynamic values of SDRs could be a problem at night and amplified antennas. It seems that the Noise Floor is really higher at night and I think it is because you get so muach RF from powerfull European station. Another interesting factor is, that the noise floor seems to be higher when listening to the RF-recording afterwords, - it should be ok when you are processiong the file afterword, but you have take into consideration when comparing the pictures taken from the real listening situation or afterwords.

The results
The conclusion is as earlier reported by several dxers: sdr-receivers are best at low-noise environment (for hard-core-dx) and low noise antennas. However looking at the IQ, you have to take into account the price of the rx (around 400 euros, maybe 1/4 of the "normal" analog rx) - the ability to see the Spectrum and measure the frequency to at least to a Hz. And, finally - to record a segment of the band for later analysis or using the machine to transfer the listening moment to a more suitable time and date!

Conditions at the Equinox-date
Overall conditions have been rather good this weak with a lot of NA, CA and South American signals noted. However, I have had no time to do serious DXing so far and it seems we are going into a at least minor storming towards the next Sunday. Hopefully something can be heard before that.
Some stations like PJD-2 Neth.Antilles 1300, R Viva Cali 1290.27 (split!) etc was heard on Equinox date. I think at least for Scandinavian hard-dx-hunters we are approaching the times of Andean DX later this season.
Hope to get something from Far East or Australia (Well, the X-band has been poor this Spring) before I have to go the the field to pick up my FE Bog - the snow is disappearing just now!

New Laptop tests going on
Finally got a new Laptop to check. It is also an ACER model (WLMI 6463) and it seems to have a PSU which does generate noise. But a new machine can be run with the battery for at least 2 hours, so it should do the work, but not unattended. Hope to get a second battery as well or a better battery. With it´s 2 GB of memory I hope to run simultaneously two or more sdrs also...

73 TK


Bjarne Mjelde said...

Interesting! You mention that the noise floor appears to be higher when listening to a recording than when it was recorded, but so is the signal. So I believe that the S/N ratio is not different. For more on the IQ:

TK said...

Yes Bjarne; I just mentioned it that looking at the pictures (either screen dumps of the original listening or afterwards runnig Svue & data) can look different. I think the S/N is the same however.