KiwiSDR, SDR-14 and possible cheaper options?

[ChrisSmolinski]

Mouser has some of the KiwiSDRs in stock, board only, you need to buy the Beagle CPU separately. If anyone is interested in getting a KiwiSDR, better hurry, these things sell out in a day or two, typically.

https://www.mouser.com/ProductDetail/Seeed-Studio/110060489/?qs=5hdTdOtYSo8Dmq6annahPw%3D%3D

[Charlie_Dont_Surf]

1)  ...  Is GPS antenna really needed or can I forego that for now?

The GPS antenna is not required, but highly encouraged, that's how the KiwiSDR corrects for errors in the ADC clock sampling frequency.

Does GPS also serve as a frequency/time reference? Can you also manually trim the reference or clock to WWV/CHU/whatever in absence of (or in addition to) that?

I notice that Kiwis can be anywhere from <10 Hz to as much as 60 Hertz (maybe more?) off from a standard. While that's not a life-or-death offset in a hobby listening scenario, it would be nice to be kind of on frequency when listening to SSB, where I notice being >10 Hz offset there.

[ChrisSmolinski]

1)  ...  Is GPS antenna really needed or can I forego that for now?

The GPS antenna is not required, but highly encouraged, that's how the KiwiSDR corrects for errors in the ADC clock sampling frequency.

Does GPS also serve as a frequency/time reference? Can you also manually trim the reference or clock to WWV/CHU/whatever in absence of (or in addition to) that?

I notice that Kiwis can be anywhere from <10 Hz to as much as 60 Hertz (maybe more?) off from a standard. While that's not a life-or-death offset in a hobby listening scenario, it would be nice to be kind of on frequency when listening to SSB, where I notice being >10 Hz offset there.

The correction of the ADC sample also corrects the tuning frequency. Of course this depends on actually getting a good GPS signal. The supplied hockey puck GPS antenna is pretty marginal, I gave up on it and went with a NOS GPS antenna meant for the wireless phone industry for their towers.

It's entirely possible the KiwiSDRs you've encountered with large tuning errors have a poor GPS signal, or perhaps even none. Click on "Stats" in the control panel in the lower right corner of the KiwiSDR window. One of the entries is for GPS, it shows the number of tracked satellites. I checked one of mine and got:

GPSacq yes, track 12, good 11, fixes 41.5k

That means it is tracking 12 satellites (the maximum it can track) and has good signals from 11 of them, and 41,500 GPS fixes since the last restart of the software, which was 23 hrs ago (when the last software update was pushed through). The number of satellites is going to fluctuate over time. If you're interested in the nuts and bolts about GPS and the KiwiSDR there's been some good discussions on the forum: http://forum.kiwisdr.com/index.php?p=/discussions   

At least 4 good satellites are required for frequency correction. So if you see fewer than that, it's not correcting. And even with 4 you don't know how good the signals are.

I suppose if you're on such a KiwiSDR, you could tune in CHU or WWV, see what the frequency error is, then compute the ppm error and apply that to the frequency of the station you're listening to. Note you need to treat it that way, it's not just a constant frequency offset error.

That said, a KiwiSDR with few or even zero GPS satellites is quite possibly the sign of a poor setup overall, including the antenna and noise/RFI levels.  It would probably be easier to just find a better KiwiSDR to log onto. 

[Charlie_Dont_Surf]

I suppose if you're on such a KiwiSDR, you could tune in CHU or WWV, see what the frequency error is, then compute the ppm error and apply that to the frequency of the station you're listening to. Note you need to treat it that way, it's not just a constant frequency offset error.

That's exactly what I have done a few times to confirm my suspicions that some receivers were a bit off frequency.

I also suspected that the offset would increase with frequency and one time I went through the trouble of confirming this at 2.5, 5 and 10 MHz. It was incrementally worse at higher frequencies (by a few Hertz, but still..). (Could not hear 15, 20 or 25 MHz at the time.)

So there is no manual trim on the frequency with the Kiwi? I guess that would have to be some sort of override to the GPS, which, in my limited understanding, seems problematic

[ChrisSmolinski]

So there is no manual trim on the frequency with the Kiwi? I guess that would have to be some sort of override to the GPS, which, in my limited understanding, seems problematic

The GPS based calibration works, but only if you have enough satellites. My guess is some users throw their GPS antenna on the desk and hope for the best. Often these same users hook up a coat hanger as an antenna and also hope for the best 

There is a manual option KiwiSDR owners can perform, instructions from the KiwiSDR admin page:

To manually adjust/calibrate the ADC clock (e.g. when there is no GPS signal or GPS correction is disabled) follow these steps:
Open a normal user connection to the SDR
Tune to a time station or other accurate signal and zoom all the way in
Higher frequency shortwave stations are better because they will show more offset than LF/VLF stations
Click exactly on the signal carrier line in the waterfall
On the right-click menu select the cal ADC clock (admin) entry
You may have to give the admin password if not already authenticated
The adjustment is calculated and the carrier on the waterfall should move to the nearest 1 kHz marker
Use the fine-tuning controls on the IQ extension panel if necessary

You can fine-tune after the above steps as follows:
Open IQ display extension
Set the receive frequency to the exact nominal carrier (e.g. 15000 kHz for WWV)
Press the 40 button (i.e. sets mode to AM with 40 Hz passband)
Set menus: Draw = points, Mode = carrier, PLL = off
Adjust the gain until you see a point rotating in a circle
Use the Fcal buttons to slow the rotation as much as possible
The total accumulated Fcal adjustment is shown
A full rotation in less than two seconds is good calibration

[Charlie_Dont_Surf]

Often these same users hook up a coat hanger as an antenna and also hope for the best 

Yeah, I've noticed.