[Lowfer] Wolf with SDR-IQ

[Garry and Linda Hess]

Thanks Lawrence for your detailed comments.

I have my SpectraVue software set up rather like you described, except I 
had the noise blanker on (I'll keep it off in what follows). Also, I use 
+24 dB IF gain as recommended in the SpectraVue Manual (p.32 of document 
version 1.29, Sept 20, 2007). And I don't understand how you set up a 
500 Hz bandwidth. My USB mode doesn't allow bandwidths under1 kHz so 
I've been using a low cutoff frequency of 200 Hz and a high cutoff of 
1200 Hz. That lets me work with 400 Hz tones my ears prefer, but also 
800 Hz or 1000 Hz tones when desired.

I repeated Wolf calibration. this time applying a 100 kHz GPS-referenced 
signal directly to the SDR-IQ tuned to 99 kHz, rather than summing it 
with my antenna input. As you reported, f error values versus time were 
quite stable. I 'm guessing the excessive variation I saw previously was 
because static crashes via the antenna were impacting the frequency 
measurements. It was not a Loran-C issue because I used a 137 kHz signal 
originally and my preselector passes 130-450 kHz. To force f error to 
zero I must specify a center frequency of 973.047 Hz in the Wolf Config 
tab under Receive Options, even though the tone applied is 1000 Hz. This 
is not the case when I use an IC-706MkIIG as the receiver. Then Wolf 
does measure 1000 Hz when the input is 1000 Hz. Perhaps this offset has 
something to do with the virtual audio cable (VAC) I run to let 
SpectraVue drive Wolf.

I've calibrated the SDR-IQ internal sample clock frequency as described 
on pp.73-77 of the SpectraVue Manual. As Lawrence points out, this 
varies somewhat with temperature. Stan, W1LE, wondered if an external 
reference could be used. I asked RFSpace about that before buying the 
SDR-IQ. The answer I got from Pieter was: "None of the units can be 
locked to GPS. If you have a generator that is GPS locked, you could 
drill a hole and feed the signal into the ADC. Some people have done it 
and it is not that hard. It does not have to be at 66.666 it could be in 
the vicinity and you can tell the software what you are using." Now that 
I know Wolf and QRSS modes work, I'll do the modification.

I normally run my IC-706MkIIG with an external fan blowing air over it. 
That keeps the internal fan from kicking on and causing momentary shifts 
of 1 Hz or so. For ARGO to display frequency correctly with the SDR-IQ 
at room temperature, a "display frequency" entry of 1020.7 is needed 
when "measured frequency" is 1000. If the external fan is running 1020.4 
should be used instead. The value for the 706 radio is 918.635. Needless 
to say I've made notes on these numbers and recheck them frequently 
since they will change with time as well as temperature.

I have also calibrated my sound card with a 1000 Hz tone referenced to 
GPS (thanks Neil, W9NU). My PC is also a Dell, model Dimension E521 with 
an Athlon dual core processor clocked at 1.9 GHz. The CPU load barely 
notices SpectraVue, even when the maximum sampling rate of 196 ksps is 
used. In fact, using the maximum rate with SpectraVue 3, beta (available 
at http://www.moetronix.com/beta.htm) actually seems to help one of the 
problems I had with SpectraVue 2.34; namely, stopping on its own after 
running  short, random periods.

73,
Garry, K3SIW, EN52ta, Elgin, IL