General discussions
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Postby vipersan » Sun Apr 10, 2016 1:55 pm

Yes indeed VK2KIT..
I think I proved it will work just fine with a TCXO ...
..and could have been retrofitted relatively easily ..replacing the original Osc ...if the lands/pads had been a little larger ...and as you say adds little to the build cost.
Perhaps the designers will indeed consider this update for future versions.
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Postby F1BJB » Fri Apr 29, 2016 3:02 pm

Instead of incorporating a TCXO I think it would be more useful to allow the use of
an external 24 Mhz reference.
It would allow having several SDRplay in perfect sync.
May be also receiving a known reference signal and locking the 24MHz to it for use by other devices.
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Postby VK2KIT » Sat May 07, 2016 4:41 am

IMHO, an internal TCXO is an absolute must in any receiver expected to operate narrow bandwidth modes and provide coverage up to 2Ghz.

Using a standard xtal reference crystal in the SDRPlay was a big mistake (in my opinion). Particularly since their main competitor advertises the fact that it's receiver uses a TCXO and has a frequency accuracy/stability of better than +-1.5ppm over a relatively wide temperature range.

The standard SMD reference crsytal used in the SDRPLay is a NX2520S. According to the specs, this crystal is rated at a fairly 'casual' +-10ppm.
A +-10ppm error at 400Mhz is +-4khz and at 800Mhz, it is 8Khz!

There is no fine tuning (crystal netting) of the reference crystal either in the SDRPlay, so there is not even any way to manually adjust it to compensate for manufacturing tolerances of the crystal or it's surrounding passive components.

Regardless, a potential frequency error of this magnitude is totally unacceptable when you are trying to monitor V/UHF NFM, SSB, or CW signals.

By comparison, the Airspy 's internal TCXO is rated at +-1.5ppm, which equates to a maximum frequency error of only 600Hz at 400Mhz and 1.2Khz at 800Mhz and while even this level of error is undesirable for some. At least, In the case of the Airspy, you have the option to connect a more accurate external reference.

Don't get me wrong, I'm all for having a software derived ppm adjustment in the SDR platform to provide some degree of 'fine tuning' compensation for a small, but inevitable reference error. But, software derived ppm adjustments do not compensate for frequency drift caused by temperature changes in the crystal and should not be used to 'carpet over' a sub-standard reference design.

The SDRplay is an amazing piece of equipment considering the relative simplicity of design (thanks to the mirics tuner chip) and price. My tests on VHF and UHF show a sensitivity and noise floor better than anything else I own, including the main competitor. It's just a shame it is let down by such a poor choice of frequency reference.

I'm not a betting man, but if I were, I'd put a dollar or two down on the table that a TCXO will feature in any subsequent 'Play' model/s :)
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Postby micked » Wed Oct 04, 2017 8:52 pm

I did a similar rebuild of my rsp1, I found a 24Mhz tcxo on ebay and retrofitted it like in the attached pictures.

The two bottom pads is gnd,
top left is vcc (3v)
top right is signal out, I decoupled it with a 1nF capacitor.

its rock solid at exact right freq., before I had to go - 3,4 to ppm adjustment and was all over the place when I opened the outer door and the cold air got in.

more pictures here:

IMG_0267_rsz.jpg (66.47 KiB) Viewed 1195 times

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