[time-nuts] update on LTE-Lite

SAIDJACK at aol.com SAIDJACK at aol.com
Sat Nov 22 21:17:36 EST 2014

I would not worry too much about the RTV, more about damaging the nice  
TCXO. That part is by far the most expensive and valuable component on the  
boards. It's not your good old $10 style TCXO.. 
We were not aware and did not know of the beat frequency causing some  
spurs until the day I posted my findings and suggestions, but there is an easy  
way around the issue as I had discussed at that time as well.
The easiest way to avoid the beat frequency spurs when using an external  
oscillator is to use a splitter with high isolation on the RF output of the  
oscillator, and to put an LC filter on the EFC pin of that oscillator. One 
(CMOS  compatible) output of the splitter goes to the LTE-Lite MMCX 
connector, the  other output can be used for your circuitry or instruments etc.
Depending on the isolation capability of the splitter I bet there won't be  
anything coming through. Instead of a passive splitter a simple CMOS gate 
as a  buffer also provides massive amounts of isolation from the 20MHz RF  
floating around the LTE Lite board.
In either way the spurs are quite low if I remember correctly, so even  a 
passive splitter with 40dB or so isolation will likely push the spurs below  
the noise floor of the oscillator I would think. The secondary path into the 
 OCXO could be through the EFC output, and that can be easily filtered out 
by  using a small RC or LC filter, say 22uH into a 100nF cap mounted onto 
the OCXO  EFC pin. That should squelch any RF on the EFC line. Since most 
OCXOs have an RC  filter built into the EFC pin anyways (usually a 30K Ohms or 
higher series  resistor into the capacitance of the varactor diode at the 
least) I don't think  much of the 20MHz would come through the EFC line, most 
of it probably through  the RF pin.
There is a 220 Ohms series resistor on the EFC output of the LTE-Lite  
anyways, so just putting a 10nF to ground on the OCXO EFC pin would already  
create a low pass filter with a 70KHz cut off frequency, so that single cap by  
itself may be sufficient already to get rid of any 20MHz RF floating around 
the  EFC line. Definitely use a shielded coax cable for the EFC line 
though, not just  a simple wire.
On the 10MHz boards the DIP-14 TCXO is soldered onto the board for best  
performance and mechanical stability, but since it only has four pins in a  
DIP-14 configuration it is very easily removed from the PCB with a proper  
solder-iron if that is desired.

Begin forwarded message:

Cc: _time-nuts at febo.com_ (mailto:time-nuts at febo.com) 
Subject:  Re: [time-nuts] update on LTE-Lite
Reply-To: _GandalfG8 at aol.com_ (mailto:GandalfG8 at aol.com) , Discussion of 
precise  time and frequency measurement <_time-nuts at febo.com_ 
(mailto:time-nuts at febo.com) >

Hi Said,

Many thanks for your  reply.

I'd realised that R2 and R3 were in  the paths of alternative power feeds  
but had managed  to convince myself that both resistors were shown to be  
fitted  in your auction photos, although I can now see  quite clearly that 
R2 is  fitted, R3 isn't,  whoops:-)

I was hoping that removing the  TXCO might be reasonably straightforward, 
was after all  your suggestion:-), but am now concerned that the RTV might  
have  flowed under any components perhaps not fully  seated and didn't want 
to take the  risk of damaging  anything. I'd also hoped it might prove 
possible to remove  the onboard TCXO power by breaking one of the tracks on 
LTE-Lite module  itself but it sounds like that might  have been a bit too  

Whilst I'm  pretty sure I would have stuck with the 20MHz version  anyway,  
the initial enthusiastic rush did mean nearly 40 of us had  already  bought 
them before your comments regarding  the harmonic  mixing and the 
suggestion to 
use the  19.2MHz version reached  the list, so to some extent at least that 
might help explain the  numbers:-)

Anyway, thanks very much  again for making these available, I certainly  
don't  see this as a significant issue so it's time to dive in and  worry  
the finer details  later.

Just out of interest, on the 10MHz  version without the onboard  TCXO, did 
the DIL  oscillator end up socketed or  soldered?



In  a message dated 22/11/2014 18:01:18 GMT Standard Time,  
_saidjack at jackson-labs.com_ (mailto:saidjack at jackson-labs.com)   writes:


CC'ing  time nuts..

R2 and R3 are  stuffing options, see the schematics in the user manual.  
Typically you don't have to solder anything. The  default is set for the  
low-noise 3.0V to be fed to  the DIP-14 tcxo for best  performance.

On removing  the SMT Tcxo, this is not easy, but possible with a heat gun.  
Its easy to melt the adjacent switches though when  doing that. The RTV 
it  should just peel off, but  we have not tried that yet. There is no way 
just  remove power to the internal Tcxo  unfortunately.

This is why  I had suggested the 19.2MHz version for people who want to  
the external oscillator option, because that won't beat  with your  
oscillator close-in. I was a bit surprised  that so few of those 19.2MHz 
units  sold 
compared to  the significant numbers for 10/20MHz units. In either case I  
think the resulting beat spurs are typically lower  than many other GPSDOs 
oscillators have in their  spurs, the CSAC with its spurs comes to  mind..

Hope that  helps,

Sent from my  iPad

On Nov 22, 2014, at 6:08, __GandalfG8 at aol.com_ (mailto:GandalfG8 at aol.com) _ 
(mailto:GandalfG8 at aol.com)  

Hi  Said,

Sorry to bother you again, I'm not  sure is this is an oversight or  
deliberate but I've  just noticed that R2 has not been fitted to my  
I'm a bit concerned as this will  affect power to the external  oscillator 
and R2 would  be difficult to fit now that SW2 is installed.
I may have  missed this if it was mentioned on the Time-Nuts list  but  
there's a lot there to look through so thought it best to  ask you  direct.



In  a message dated 30/10/2014 23:30:40 GMT Standard Time, 
__saidjack at jackson-labs.com_ (mailto:saidjack at jackson-labs.com) _ 
(mailto:saidjack at jackson-labs.com)  writes:

Hello  everyone, 
We wanted to give you an interim update on the  LTE-Lite  Evaluation kit 
builds. We are making good  progress on the assembly. We are  expecting to 
within the announced time frame, and are guiding the  factory on a daily 
We are  using the time to improve the firmware and have  made some upgrades 
with the help and efforts of a very well-known Time Nut  (thanks much!) who 
I am certain will identify himself  in due time.  This development activity 
has revealed a  sensitivity in the GPS  receiver: the unit should not be  
changed from mobile mode to Position Hold  (Timing)  mode ROM/Flash 
firmware or 
vice versa while power is  enabled,  this could lead to Flash memory 
corruption.  We are thus shipping the unit  with a solder jumper that will 
soldering-in two pins to get out of  Timing mode and  into mobile mode so 
as to 
avoid the possibility of a user  accidentally inserting a jumper with power 
supplied  to the unit, which  could then corrupt the GPS Flash memory. We 
also been able to upgrade  the GPS Flash firmware in  close cooperation 
the vendor of the GPS  receiver  to make it more optimal for operation in a 
GPSDO, and these  efforts have given us a GPS Flash firmware release that  
works well with  our GPSDO algorithms and TCXOs. We  will upgrade all of 
GPS receivers  prior to  shipment with this specialized firmware release. 
We also  have some good news on the 10MHz versions of  the board: the 10MHz 
DIP-14 TCXOs are scheduled to arrive at our factory  in about 5 weeks, so 
that will pull-in the delivery  schedule  significantly. We will continue 
keep  track of the schedule and update  you with any changes.  

Lastly there has been some fairly intense  discussion recently about 
counter-fit FTDI serial  chips getting  permanently disabled by the latest 
software drivers and thus  rendering affected  equipment unusable. Many 
have been published on  Time-Nuts so please consult the archives for more  
information on this  issue. 
We use  FTDI chips on many of our products, such as the  CSAC GPSDO,  
Mini-JLT, LC_XO Plus kit, and also this LTE-Lite Eval kit.  We  are pleased 
announce that we have verified with  our suppliers that all  of our 
shipments in 
the past  and in the future have and will continue to  use genuine FTDI 
Close inventory control and counter-fit policies  are  one advantage of 
manufacturing in the USA versus in  Asia. 
More later,  
Said  Jackson 
Jackson Labs Technologies,  Inc.  
1635 Village Center Circle, Suite  150  
Las Vegas, NV 89134  
Tel. (408)  596-0600 
Fax. (702) 233-1073 
__saidjack at jackson-labs.com_ (mailto:saidjack at jackson-labs.com) _ 
(mailto:saidjack at jackson-labs.com)  
__www.jackson-labs.com_ (http://www.jackson-labs.com/) _ 

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