10 MHz Reference for iDirect hub and BUC

It is not normal to try to use a stand alone iDirect modem as a source of 10 MHz reference. I suspect it might work, but be careful and see my comment in message further down about frequency accuracy and stability.

You should really use a proper 10MHz reference equipment.

A high power BUC, such as 80W, probably has inbuilt monitoring telemetry regarding things like power output level, temperature, power supply current, up-converter oscillator lock/unlock and mute status.  If you turn off the 10 MHz TX reference from the iDirect equipment the BUC should signal "Unlock alarm", "Missing 10 MHz reference alarm" and "Output muted". These alarms should clear when the iDirect TX 10 MHz reference is turned on.

You will need a suitable power supply for the BUC. The iDirect modem may be damaged if you attempt to power the 80W BUC direct from the modem.

The power supply cable arrangements to the BUC are important. If it is a separate AC mains or separate pair of DC power supply cables then there is less problem as the L band coax cable will go from the iDirect modem to the BUC and be able to carry both the L band signals and the 10 MHz reference.  If the power supply arrangements involve interfering with the coax cable then any combiner, splitter, DC block, power injector etc needs to be designed such that both the 10MHz and the L band signal can reach the BUC. Make sure all connections are perfect. You don't want AC mains or high current DC coming back along the BUC coax outer, or even the LNB cable!

80W RF is dangerous. Do not power the BUC unless the output is connected to the antenna or a suitably rated dummy load. Don't get any body part in front of the feed/antenna. Transmit to a satellite only under control from the NOC and start with low power.

Best regards, Eric.

I think this is the specification for the Terrasat 4 way divider/combiner:
https://www.terrasatinc.com/documents/014CombinerDividerDataSheet020114.pdf
It is specifically designed for this application. Port 1 passes the 10 MHz (and FSK and L band if required). Port 2 passes the L-band but blocks 10MHz.

If it has N type sockets check that your plugs fit. The centre pin  of 75 ohm N type plugs is fractionally too small to fit 50 ohm N type sockets.

I've looked at iDirect hub specifications and it seems that line cards only pass out 10 MHz when used in 12000 series hubs. You have a 5IF hub, not a 12000 series hub. I've looked at a picture of a 5IF/20slot hub and there were no RCMs installed at the back.

Ideally you should have a redundant 10 MHz reference, plus 10 MHz multi-splitter with outputs to all equipment racks at the hub teleport. These station 10 MHz reference supplies will then go to the iDirect hub and the Port 1 on the Terrasat combiner.

If you use an iDirect modem as your 10 MHz supply for the BUC, this is cheap solution with poor frequency stability. I would expect it to work but there may be problems with frequency accuracy, stability and reliability. It would be a good idea to have a hot spare available and it would be worth looking inside the modem to see if you can adjust the reference frequency module once it has warmed up for 24 hours and then every month or so. Adjustment may be possible using a small screw or potentiometer. If adjustment is not possible is there any way to get at the 10 MHz supply inside the iDirect hub?. Have you asked around your teleport to see if there is already a generally available 10 MHz reference distribution supply ?

Read more here: https://www.satsig.net/cgi-bin/yabb/YaBB.pl?num=1366883151

Does anyone know the accuracy and stability of the 10 MHz from an iDirect modem, when it is free running and not in a network. i.e. used only for its 10 MHz output?

If this is true "The 10 MHz reference used at a remote site may derive its accuracy from the symbol rate of the outlink carrier from the hub. " then you have a problem and should get yourself a stand alone 10 MHz reference equipment rather than modem..

You need a highly accurate, stable and reliable supply of 10 MHz for the BUC.

I recommend a proper 10MHz source. I've used a pair of redundant ovenised crystal oscillators with no trouble. They need adjusting 24 hours after installation and then annually.

An alternative is a GPS locked device. You need a GPS antenna outdoors and the oscillator needs to continue and be stable when the GPS signal is occasionally lost.

Ask your iDirect modem supplier what is the accuracy and stability of the 10MHz from a modem when it is free running and not in a network.

Get hold of the specification/manual for your model of 80W Terrasat C band BUC.  Read and see if it has an internal 10 MHz reference, as an alternative to an external 10 MHz reference supply. Some models have "Internal 10MHz reference option automatically switches to internal reference when external reference is not detected."

What does IFU mean ?

Does your Terrasat IFU contain an 10 MHz Oven-controlled Quartz Oscillator (OCXO) ?.

If yes, your problem is solved.

Note: The front panel contains a small hole that is used to access a trimpot (when the OCXO is installed) that enables users to adjust the frequency of the 10 MHz reference signal.

Best regards, Eric.

I repeat:  Does your Terrasat IFU contain an 10 MHz Oven-controlled Quartz Oscillator (OCXO) ?.

Since the inclusion of a 10 MHz reference in the interface unit (IFU) is an option you need to check with your order/delivery details and model number/options etc.

I would look inside. You may need to do this anyway to check positions of various jumpers. Look through the small hole (if any) in the front panel. Is there a visible adjustment trimpot for the frequency adjust?.

If you power up the IFU alone and not connected to anything else do you see 10 MHz on any outputs.

Another question: Does your iDirect 5IF hub have any 10 MHz oscillators (RCM-A and RCM-B) in it ?

Hi,
thanks for your massage.
Yes, I think have OCXO ( i seem block diagram).  iDirect told me that it will not provide 10Mhz from HUB.

thanks for your message.
I will feedback to you soon.

To deal with the different BUC LO frequency (changing from 7375 to 4900 MHz ) you need to recalculate  the modem L band transmit frequency and also change from carrier inverted to carrier upright.

Example:
BUC LO=7375 MHz
Wanted BUC output transmit frequency = 6000 MHz
Modem frequency = 7375 - 6000 = 1375 MHz
Inverted carrier.

It is inverted in this case  since the LO frequency is higher than the wanted output frequency and you are selecting the lower sideband in the BUC power amplifier. The upper sideband output from the mixer at 13375 MHz is hopefully not being radiated by the BUC !

BUC LO=4900 MHz
Wanted BUC output transmit frequency = 6000 MHz
Modem frequency = 6000 - 4900 = 1100 MHz
Upright carrier

Here are some examples of different C band BUCs, the RF output range and the input IF range and the upconverter local oscillator frequencies:

C band name Range (MHz) RF   IF range   LO frequency
Std C 5850 - 6425             950-1525  7375 / 4900
Ext-Palapa 6365 - 6725       1075-1435  7800 / 5290
Ext C 6425 - 6725             950-1250  7675 / 5475
Full C 5850 - 6725            950-1825  7675 / 4900
Insat C 6725 - 7025           965-1265  5760
Insat C (Inv) 6725 - 7025     975-1275  8000


Please restore your original posting and image (far above) back to the original version.

Eric is right about the spectral inversion,and then the software make the calculation (you do not need to calculate the L band frequency, is automatically) I'm not sure about the 10MHz, because the XLC11 datasheet doesn´t shown anything about transmiting the 10MHz beside in the upconverter configuration the option exist, I guess is only for remotes.

In our case we are using this


https://www.oscilloquartz.com/files/1357907121-da_453x.pdf

You just need to be sure that the power of this 10MHz is arriving with the correct level into you BUC +/-5dBm, or you will have CRC32/8 in 8PSK/16APSK

** image added by forum admin **

Thanks for your reply. let me check and update.