SDRPlay TCXO?

General discussions
g1hbe
Posts: 216
Joined: Sat Jan 17, 2015 3:28 pm
Location: Cheshire

Re: SDRPlay TCXO?

Postby g1hbe » Sun Aug 23, 2015 11:14 am

OK, it's sorted. Under a magnifying glass and a ten-billion watt lamp, I could see that one of the c's was fractured. I didn't have any 18pf smd caps, but a 15 pf leaded part got the frequency to within 100 Hz. After a re-tweak of the frequenc trim setting, the strange offset has now gone away. Job done. Sorry for wasting your time.
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Andy

Tech_Support
Posts: 202
Joined: Mon Jun 01, 2015 7:00 pm

Re: SDRPlay TCXO?

Postby Tech_Support » Sun Aug 23, 2015 1:51 pm

Many thanks for the update.

Sincerely

SDRplay Tech_Support
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vipersan
Posts: 19
Joined: Thu Mar 10, 2016 12:04 am

Re: SDRPlay TCXO?

Postby vipersan » Tue Apr 05, 2016 10:15 am

This subject has grabbed my interest ..because I am trying to get a Cband Jaero setup ...up and running with SDRplay ..
It works OK but the drift is noticeable ..
Reading the previous posts I am prepared to retrofit a TCXO but the problem is locating something suitable ..
well This one looks like it would do the job
NDK 24MHz TCXO SMD ENA3291A
It can be got off ebay ...or indeed quite a few places ..but search as I might I cannot locate a pdf or data sheet for it.
So ..no idea of the pinouts ..supply voltage min max etc ..nor its physical size ..
Anyone know where the data sheet might be got ?
rgds
Vipersan
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vipersan
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Re: SDRPlay TCXO?

Postby vipersan » Tue Apr 05, 2016 2:27 pm

Gave up searching for the pdf for the above TCXO ...and found this one instead from Farnell ..
Less than £1 each so ordered 2 ...and the pdf datasheet is available.

TXC 7Q-24.000MBN-T TCXO, GPS, 24MHZ, 3.2 X 2.5MM, CLIPPED SINE

So will look into retrofitting one in due course..
I just hope it is suitable ...so would appreciate some feedback from SDRplay tech support
rgds
VS

http://uk.farnell.com/txc/7q-24-000mbn- ... dp/2325488
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Tech_Support
Posts: 202
Joined: Mon Jun 01, 2015 7:00 pm

Re: SDRPlay TCXO?

Postby Tech_Support » Tue Apr 05, 2016 2:55 pm

Hello Vipersan,
It is hard to be certain that this TCXO will be suitable as we have never tried using it, but from the specs, it looks as though it should be ok. Please be aware that you will need modify the PCB it implement this and this will involve removing the current Xtal oscillator components: X1, C65 and C66 and wiring in the TCXO module output to X0 (pin 22) of the MSi2500.You will also need to find a way to route power and ground to the TXCO module.

You will most likely need decent SMD soldering/re-work kit and experience to accomplish all of this along with a very steady pair of hands and good eyesight!

I am afraid that I have to also warn you that these changes will invalidate your warranty for the RSP, but as long as you are comfortable with that I wish you good luck and look forward to hearing about how you get on.

Sincerely

SDRplay Tech_Support
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vipersan
Posts: 19
Joined: Thu Mar 10, 2016 12:04 am

Re: SDRPlay TCXO?

Postby vipersan » Tue Apr 05, 2016 3:06 pm

Many thanks for the prompt reply ..
I am a TV engineer by trade ..and have worked with SMD devices before ...
but that said ..I am getting older and although my hands are still steady ..my eyesight isn't what it used to be ..lol
I will use Chip Quik to remove the components ..as this will reduce any chance of heat damage ..and I understand it will void my warranty sadly.
Last question ..
would you connect the output of the TCXO directly to pin XO (22) or cap couple it ? ..
if so could you suggest a value for this cap.
best regards
VS

Tech_Support
Posts: 202
Joined: Mon Jun 01, 2015 7:00 pm

Re: SDRPlay TCXO?

Postby Tech_Support » Tue Apr 05, 2016 5:01 pm

Hi Vipersan,
I would recommend AC coupling the TCXO in case it has a bias voltage on it. Pin 22 on the MSi2500 has its own internally generated bias voltage. The impedance won't be very high as the Xtal oscillator uses a simple CMOS inverter with resistive feedback around it. We are not sure what value the resistor actually is, but it ought to be several K ohms. As such the input resistance is likely to be in the range of several hundred ohms to several k-ohms. Hopefully, the TCXO module will have sufficient drive capability. I would recommend starting with a 1nF coupling capacitor and see how you get on.

Sincerely

SDRplay Tech_Support
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vipersan
Posts: 19
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Re: SDRPlay TCXO?

Postby vipersan » Sun Apr 10, 2016 1:31 am

So ..My warranty is now void having removed the 24mhz crystal..
The 24mhz TCXO is temporarily hung with fine wires on a small piece of stripboard ...
This may be a problem to fit as it has a slightly larger footprint than the original crystal ..
No capacitors have been removed from the SDRplay pcb as this didn't seem neccessary ..
the output from the TCXO was ac coupled to pin 22 of the MSI2500 chip with a 220pf capacitor ...and the needed 3v DC supply was picked up from the 3volt regulator U15 which in turn is fed directly from the 5v USB supply ..
The AFC pin on the TCXO is grounded along with pin 1
So PINS 1 and 2 of the TCXO are grounded ..
3v supplied to pin 4
output cap coupled from PIN 3 to the osc in of the MSI2500 chip ..
It donesn't look pretty but it IS working ..
I'm attaching photos of the lashup ..along with an active screengrab of the sdr pcb ouputting ACARS (Aero data)
rgds
VS
Attachments
ACARS.jpg
ACARS.jpg (240.14 KiB) Viewed 2633 times
DSCF0088.JPG
DSCF0088.JPG (203.89 KiB) Viewed 2633 times
DSCF0086.JPG
DSCF0086.JPG (218.18 KiB) Viewed 2633 times
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vipersan
Posts: 19
Joined: Thu Mar 10, 2016 12:04 am

Re: SDRPlay TCXO?

Postby vipersan » Sun Apr 10, 2016 11:57 am

Tidied this up and the TCXO is now fitted on a similar but custom made pini pcb ..
The SDR play pcb left overnight but not enclosed (without case) remained stable and on frequency ...but now the pcb is once more enclosed I am having to make small changes and track the T stream data ...
So although improved heat still plays a part ..and drift is still in evidence ..
I cannot work out why ...?
Any suggestions ...or help from Tech Support would be most welcome.
I would estimate the amount the data I am after has shifted from 1.534.748.000 to 1.534.728.000 in a little over 5 hours (RSP pcb now encased).
Which IS better than before ..but still I'm not happy as I cannot set the frequency and leave it unattended to log Aero data...
rgds
VS
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VK2KIT
Posts: 2
Joined: Sun Apr 10, 2016 12:45 pm

Re: SDRPlay TCXO?

Postby VK2KIT » Sun Apr 10, 2016 12:51 pm

Hopefully V2 will incorporate a TCXO like this:

http://mouser.com/ProductDetail/TXC-Cor ... KcKfJZE%3d

On the face of it, the above 24Mhz 0.5ppm @ 3V TCXO, appears to be the perfect candidate :)

Would only add a couple of dollars to the manufacturing cost too..
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