[App_rpt-users] RTCM Simulcast question

[Kevin Custer]

There is one thing everyone is missing in this discussion.  If the 
intention of this oscillator is to be used in duplex service, be aware 
that the Si series of products may not have the spectral purity for 
duplex applications.  By spectral purity, I mean transmitter side band 
noise.  Stability using GPS is likely easy, but making an oscillator 
clean enough isn't always easy.

I say this because there has been a great deal of interest in making 
programmable channel elements for older crystal radios using the Si 
series.  These modules exist, but testing has shown that they don't have 
the noise specification required for duplex operation.  This means it 
may be more challenging or impossible to make them work in some duplex 
applications.  Of course, this depends on how the OCXO/Si is used.  If 
it were driving the loop reference of a free running on-frequency 
oscillator, locked by PLL, then you'd have the best of all worlds  - 
synthesized frequency reference, low transmitter side-band noise, and 
the ability to modulate it.  Something similar to the GE MASTR II PLL 
exciter and its operation could be considered.

Kevin Custer




On 6/6/2016 12:06 PM, David McGough wrote:
> If you GPS-discipline that OCXO, I think it would be more than adequate.
> Since you've already got the 1 PPS GPS signal, all that should be needed
> in addition to the OCXO/Si5351 is a little $3 Arduino board (like:
> http://www.ebay.com/itm/131702108124 ) to program the desired output
> frequency(s) and perform compensation.
>
> $16 for an OCXO ---NICE! ...The whole project maybe $25!
>
>
>
> On Mon, 6 Jun 2016, Joe Moskalski wrote:
>
>> I mentioned this to someone else, QRP Labs has a kit that creates a OCXO
>> around the Si5351 chip. here is the link:
>>
>> http://www.qrp-labs.com/ocxokit.html
>>
>> If you couple this with another kit of theirs you can program it it any
>> frequency you want. My only thought is would it be accurate/stable enough.
>>
>> http://www.qrp-labs.com/progrock.html
>>
>>
>>
>> <https://www.avast.com/sig-email?utm_medium=email&utm_source=link&utm_campaign=sig-email&utm_content=webmail&utm_term=icon>
>> Virus-free.
>> www.avast.com
>> <https://www.avast.com/sig-email?utm_medium=email&utm_source=link&utm_campaign=sig-email&utm_content=webmail&utm_term=link>
>> <#DDB4FAA8-2DD7-40BB-A1B8-4E2AA1F9FDF2>
>>
>> On Mon, Jun 6, 2016 at 11:36 AM, David McGough <kb4fxc at inttek.net> wrote:
>>
>>> Hi Joe,
>>>
>>> While on the subject of the Si5351 chips, the application of converting
>>> one reference clock to a secondary frequency is what they were designed
>>> for. So, since you've already got a GPS reference, this -might- be an
>>> inexpensive starting point...For this application, you obviously won't
>>> need all the bells and whistles presented in this article! See:
>>>
>>> http://www.knology.net/~gmarcus/Si5351/Si5351_VFO_QEX.pdf
>>> http://www.knology.net/~gmarcus
>>>
>>> Note that I would replace the Si5351 25MHz reference with a decent TCXO
>>> (available on ebay, etc.)....Note that I haven't used the Si5351 with an
>>> RTCM, there may be simpler/better ways???
>>>
>>>
>>> 73, David KB4FXC