Re: Pluto QO-100 and SDR Radio- changing ref frequency question

Chris Wilson

Hello Siegfried,

Friday, April 9, 2021

Thanks again Sigi. Would a Leo Bodnar dual output device be adequate, phase noise wise?

Best regards,
Chris 2E0ILY mailto:chris@...

SJ> 40 megs gives best signal quality ... and if you add a tcxo with 40 megs
SJ> ... use one with LOW PHASE NOISE

SJ> same when using an external reference ... low phase noise and jitter is
SJ> needed

SJ> greetz sigi dg9bfc

SJ> Am 09.04.2021 um 12:13 schrieb Chris Wilson:
Hello Siegfried,
Friday, April 9, 2021
That's a good explanation to jdow, and one even I believe I have understood, thanks Sigi.

Best regards,
Chris 2E0ILY mailto:chris@...

SJ> the fpga has its own clock
SJ> the 40 mhz is the reference of the tranceiver chip not the fpga
SJ> it is for the pll of the mixer(s) in the trx chip ... so it
SJ> influeces frequency, spurii etc but not how fast the fpga is clocked
SJ> there are 3 clocks inside pluto
SJ> 24 megs for usb chip
SJ> 33.333 megs for fpga
SJ> 40 megs for the trx chip
SJ> change of reference for trx chip will not influence the fpga
SJ> now clear??
SJ> dg9bfc sigi
SJ> ps 40 megs will give a cleaner signal as 10 megs (fewer birdies and fewer spurii)
SJ> Am 09.04.2021 um 09:25 schrieb jdow:
SJ> I am not sure I understand what you mean by your question.
SJ> The question is whether the clock rate due to a crystal change
SJ> to a 10 MHz or an external clock rate of 10 MHz will affect the
SJ> ability of the FPGA to deliver the same performance as you see
SJ> when 40 MHz is used. For that matter what might happen if you
SJ> use a clock rate of precisely 33,554,432 Hz. (2^25) I suspect
SJ> the whole chip will slow down significantly at a lower crystal or external clock input.
SJ> {^_^}
SJ> On 20210408 23:41:01, Siegfried Jackstien wrote:
SJ> it is the clock of the transceiver chip not the cpu (fpga) ...
SJ> dg9bfc sigi
SJ> Am 08.04.2021 um 19:47 schrieb jdow:
SJ> If the same sample rates come out of the Pluto it
SJ> should make no difference what the system clock is,
SJ> should it? It's unclear to me whether setting Pluto's
SJ> clock to say 10 MHz is compensated for somewhere within
SJ> Pluto or not. (Does the internal CPU run at 10 MHz instead of 40 MHz, for example?)
SJ> {^_^}
SJ> On 20210408 08:59:25, Simon Brown wrote:
SJ> Well,
SJ> Let's see, at the moment SDR Console only knows about 40Mhz.
SJ> Simon Brown, G4ELI
SJ> Message-----
SJ> From: <>On Behalf Of Chris
SJ> Wilson
SJ> Sent: 08 April 2021 14:53
SJ> To: Simon Brown <>Subject: Re:
SJ> [SDR-Radio] Pluto QO-100 and SDR Radio- changing ref frequency
SJ> question
SJ> Hello Simon,
SJ> Thursday, April 8, 2021
SJ> Thanks Simon, my take, which may very well be wrong, is you can inject most
SJ> any frequency into the Pluto instead of using the stock xtal oscillator,
SJ> (you remove, or bypass the xtal oscillator), and in the firmware you tell it
SJ> what new frequency you are injecting and it does "magic digital things" to
SJ> use the new frequency.
SJ> My hopefully soon to arrive set up from the Czech Republic sends 25Mhz
SJ> through a special Bias T to the Pluto, derived from a 10MHz GPS locked
SJ> source. It also sends this to the LNB to lock that.
SJ> I am confused whether SDR Radio needs to be told of this or not, somewhere
SJ> in your great software's extensive menus was mention of the 40MHz reference,
SJ> although I can't just find it again right now, which worried me as to
SJ> whether it would be happy with the Pluto receiving a 25MHz source. It did
SJ> not appear that changing the 40MHz figure was possible...
SJ> Going to take a Paracetamol and reflect :)

SJ> Best regards,
SJ> Chris 2E0ILY mailto:chris@...> Chris,
SB>> I *think* the internal oscillator is always 40MHz, your LNB may use
SB>> 25MHz in which case the software will not need changing.
SB>> Simon Brown, G4ELI
SB>> https://www.sdr-radio.comSB> -----Original Message-----
SB>> From: <>On Behalf
SB>> Of Chris Wilson
SB>> Sent: 08 April 2021 13:44
SB>> To: main@...> Subject: [SDR-Radio] Pluto QO-100 and SDR Radio- changing ref
SB>> frequency question
SB>> 08 April 2021

SB>> If I change the reference frequency for my PlutoSDR to allow locking
SB>> it to say an external 25 MHz GPS locked source, will SDR Radio
SJ> accommodate this?
SB>> I see no way to change from the stock 40 MHz ref frequency in one of
SB>> SDR Radio's menus. Bear with me please, I am new to this....Thanks.

SB>> --

SB>> Best regards,
SB>> Chris mailto:chris@...



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