KS-24019 RFTGm-II-Rb and RFTGm-II-XO teardown, 10MHz output mod - Page 1
Forum section: electronics / testgear

author: perdrix
author_rank: Frequent Contributor
timestamp: March 02, 2018, 03:55:30 pm
content: Some time back I acquired a KS24019 shelf which was manufactured to provide 15MHz and 1PPS signals for CDMA mobile telephone systems.It comprises two boxes:The RFTGm-II-Rb which contains a Datum LPRO 10MHz Rubidium Oscillator (10MHz)The RFTGm-II-XO which contains a 10MHz OCXO and a GPS receiverand a 6-way signal splitter which takes its input from whichever of the two boxes is currently providing the 15MHz signal (IOW it has two inputs and six outputs). The 1PPS signal is routed out from the RS-422 9 pin ports on the front.In normal operation the unit operates using the Rubidium as the active unit and fails over to the GSPDO in case of failure. It is however possible to swap over to the XO as the primary. The GPS is used to discipline *both* the OCXO and the Rubidium Oscillators.There's plenty of pictures of the exterior of these out on 't web, so I won't bore you with those.Starting with the RFTGm-II-Rb general interior shot:Now a close up of near the connector into which the LPRO plugs:You'll notice the 51R1 resistor to ground, a cap to its left, a 20K resistor to ground, and the 47K5 resistor to +5V to centre the 10MHz signal on about 1.5V.The 10MHz signal is then fed into pin 9 of the Altera EPM7032LC44-15 IC at the bottom of the pic.On the other side of the IC the 15MHz signal comes out from pin 37 via jumper (E1), L100, and fixed cap (C101) and trimmer cap C102 in parallel to the input of a 15MHz bandpass filter in the centre of the picture.The output from the bandpass is then fed through a couple of amplification stages, and finally through a Mini-Circuits PLP-18-11 lowpass filter (silver part just behind the SMA socket at the RHS of the first picture).So the plan is to remove the 15MHz bandpass filterthen to take off 10MHz from the right end of the 51R1 resistor shown in the second pictureusing a 470pF radial ceramic capacitor, via a short run of coax to a 20dB Pi attenuator1made up of two 60R4 and one 249R surface mount two 1K21 and one 4K99 0805 resistors (input and output impedance 1K0 approximately) mounted on perf boardto a daughter-board2where the bandpass used to be with the output feeding in to the first amplifier (U100) via C103.I'll make another post with a look inside the RFTGm-II-XO.Footnote:1. The signal at the output of the LPRO is .55Vrms. So as to avoid clipping and other distortion, the signal level at the input to U100 should not exceed about 55mVrms(150mVpp). Prior to modification this is well over-driven with a signal of about 1Vpp.2. More details in a later post - the OCXO variant has 5V CMOS signal - need to cope with either type.

author: texaspyro
author_rank: Super Contributor
timestamp: March 04, 2018, 03:37:34 am
content: Lady Heather v6 Beta will talk to these units. The Rb and XO are independent and to fully monitor and control them you need to fire up two instances of Heather. I had to do quite a bit of work to reverse engineer the protocol and commands from the Lucent software.

author: perdrix
author_rank: Frequent Contributor
timestamp: March 05, 2018, 11:55:30 am
content: Here are the pix of the interior of the RFTGm-II-XO as promised:The main and most obvious differences are the OCXO instead of the LPRO and the presence of the Motorola GPS receiver (not sure which one). I've annotated the signals to/from the XO board.This one is of the processor board with the GPS receiver removed, showing the additional components to support the GPS board.And finally a close up of the area where the 10MHz singal enters the board. It's not obvious, but the 10MHz signal in this case surfaces at the via right next to pin 7 of the large IC. and routes from there to pin 9 as before and also a single 100k resistor to ground. The signal in this case is a standard 0-5V CMOS square wave unlike the side with the rubidium.CheersDave

author: perdrix
author_rank: Frequent Contributor
timestamp: March 05, 2018, 12:06:31 pm
content: Because the 10MHz signals differ between the two sides of the RFTGm-II, I'm proposing to build a small daughter board which will fit using double sided sticky tape to where the original bandpass filter was installed.The board will be designed so that two variants can be built. Here are my currently incomplete schematics showing the differences. The 20dB attenuation level shown for U3 which feeds the input to the MSA-0385 MMIC (U100) that follows has not yet been finalised and is likely way too high.First the Rb side variant:please note that I've not yet decided between the MC74VHC1GT04 and the MC74VHC1GT14 for the input conditioning in this variant.Secondly the XO side variant:which is much simpler as the input is already a 0-5V square wave.I'll post again when the mod is finalised.CheersDavid

author: texaspyro
author_rank: Super Contributor
timestamp: March 06, 2018, 01:34:23 am
content: I fired up my RFTG-m and the RB side reports an error after 3 hours... it says the "1PPS greater than high threshold". Well, actually it said the ROM failed, but that was due to a bug in my message processor for the ASCII time code message that has the error info... that has since been fixed.I really don't want to dig into that beast...

author: perdrix
author_rank: Frequent Contributor
timestamp: March 07, 2018, 05:21:46 am
content: Oh what a pain - working out what's causing that won't be easy.SympathyDavid

author: texaspyro
author_rank: Super Contributor
timestamp: March 07, 2018, 05:40:42 am
content: Quote from: perdrix on March 07, 2018, 05:21:46 amWell, I only bought it to add support for it to Lady Heather, and it works well enough for that... so I'm not in any hurry to dig in.Probably would first do a capacitor check and swap the LPRO (if that's whats in mine... some used a different RB)

author: perdrix
author_rank: Frequent Contributor
timestamp: April 11, 2018, 02:09:04 pm
content: I've had to revise the circuit for the Rb version as the signal level from the LPRO isn't enough to drive standard logic.Here's the revised schematic.The revised board isI'll post the OSHPark link for the board once I've confirmed it all works.David

author: perdrix
author_rank: Frequent Contributor
timestamp: October 15, 2018, 04:13:30 pm
content: After a few iterations I have revised schematics for the signal conditioning and lowpass filter circuit I'm inserting in place of the original 15MHz filter.Here's the schematic for the RB side:and here is the one for the OCXO side:I've created a single PCB that can be used to create either circuit. The signal pick-off point for RB variant is theright hand sideof C100, while for the OCXO variant it is theleft hand sideof C100. The differences in schematics are because the RB output picked off at the right hand side of C100 is an approximately 2Vppsine wave centred on 0V while the output for the OCXO is a 5V square wave.In both schematics, U3 is a Mini-Circuits LAT20+ 20dB attenuator.You can order the PCB from Oshpark:

author: perdrix
author_rank: Frequent Contributor
timestamp: October 15, 2018, 04:38:26 pm
content: Here are some pix of the installed boards - firstly in the XO side:and in the RB sideThe output level is about +17dBm and is a clean 10MHz sine wave which I am quite happy with.If you want the output level to be closer to the original output level of +23dBm you can substitute a LAT15+ for the LAT20+ attenuator.The only problem with this modification is that both sides (RB and XO) will produce an 10MHz output signal even when unlocked, so you just need to connect only to one unit and be aware when/if you loose lock.CheersDave

author: vasitse
author_rank: Newbie
timestamp: December 18, 2024, 10:07:54 am
content: Quote from: perdrix on March 02, 2018, 03:55:30 pmHi there. Did you by any chance notice if Pin 5 (lamp volt) from LPRO module, is anywhere to be found in a pin of the front panel?

author: perdrix
author_rank: Frequent Contributor
timestamp: December 18, 2024, 05:20:57 pm
content: Nope, and I no longer have the device