Economical option for precision frequency reference?

[SoundTech-LG]

I have been touring ebay for a distribution amplifier after reading that several people have used video amplifiers for the job. Decided on a Link Electronics video distribution amplifier .

This is what mine looks like, Extron ADA 6 300 MX HV, bit excessive but hey. I was originally going to get it for a Frequency Electronics Inc FE-5680A Rubidium standard, happy with my LUCENT/SYMMETRICOM Z3810AS, KS24361 RFTG/GPSDO instead.

Are you planning to mod that for 50 ohm in/out? Lots of work. I haven't used, or modded mine yet...

[Shock]

Are you planning to mod that for 50 ohm in/out? Lots of work. I haven't used, or modded mine yet...

Yeah that is the plan to initially convert it to impedance match as shown in the video, I'll look at gain at the same time. I don't think there is too much work involved, it just depends how far I take it. Makes for a nice project box either way.

In case you weren't aware there is some specs on it here.
http://www.extron.com/product/product.aspx?id=ada6300mxhv#spec

[Gandalf_Sr]

What will be your ultimate use for the device? If you are only interested in 10 MHz I'd recommend looking for a Nortel NTBW50AA - it has a cleaner 10 MHz with less phase noise and works with Lady Heather. It is much bigger though.

Steve, I took your advice and ordered a Nortel NTBW50AA from eBay, it needs a 24-48 volt power supply which gets up to 75 Watts when the heater is on full.  I found this power supply but it would be running at 100% at 75 Watts which seems a bit tight, I'll keep looking but any suggestions are welcome.

[carpelux]

Are you planning to mod that for 50 ohm in/out? Lots of work. I haven't used, or modded mine yet...

It isn't really that much work. I have one, and if I remember correctly it's replacement of only 15 resistors.

[Shock]

Are you planning to mod that for 50 ohm in/out? Lots of work. I haven't used, or modded mine yet...

It isn't really that much work. I have one, and if I remember correctly it's replacement of only 15 resistors.

Just saw w2aew did a distribution amp video yesterday some might find interesting.

[TheSteve]

What will be your ultimate use for the device? If you are only interested in 10 MHz I'd recommend looking for a Nortel NTBW50AA - it has a cleaner 10 MHz with less phase noise and works with Lady Heather. It is much bigger though.

Steve, I took your advice and ordered a Nortel NTBW50AA from eBay, it needs a 24-48 volt power supply which gets up to 75 Watts when the heater is on full.  I found this power supply but it would be running at 100% at 75 Watts which seems a bit tight, I'll keep looking but any suggestions are welcome.

When they wrote that spec they were talking about some worst case in rush current I am sure. When I tested mine it used 12 watts when warming up and about 9 watts after that. I use a good quality 24 vdc 0.5 amp wall adapter. That is what I had on hand but if buying new I would get one with a slightly higher current rating so it wasn't operating at 100% capacity when the OCXO is warming up. Absolutely no problems at all and it has been running for months and turned on/off many times. I also added a small rubber o-ring to one of the existing holes in the back of the unit and ran a power cord through it which leads to a 2.1mm connector. The wall adapter has the mating connector which keeps things nice and simple.

[SoundTech-LG]

Are you planning to mod that for 50 ohm in/out? Lots of work. I haven't used, or modded mine yet...

Yeah that is the plan to initially convert it to impedance match as shown in the video, I'll look at gain at the same time. I don't think there is too much work involved, it just depends how far I take it. Makes for a nice project box either way.

In case you weren't aware there is some specs on it here.
http://www.extron.com/product/product.aspx?id=ada6300mxhv#spec

I was aware, but still nice to see the 300, or 400mHz bandwidth. Getting the boards out/in seems to be most of the work for swapping out the terminating/source resistors.

[N8AUM]

Are you planning to mod that for 50 ohm in/out? Lots of work. I haven't used, or modded mine yet...

Yeah that is the plan to initially convert it to impedance match as shown in the video, I'll look at gain at the same time. I don't think there is too much work involved, it just depends how far I take it. Makes for a nice project box either way.

In case you weren't aware there is some specs on it here.
http://www.extron.com/product/product.aspx?id=ada6300mxhv#spec

This might be a dumb question but why the high bandwidth ? Don't most instruments add low pass filtering on their "REF" inputs ?
I picked up an el cheapo chinese video distribution amp from fle-bay, ya it's 75 ohms but so far none of my HP gear seem to mind the slight impedance mismatch. 

[bson]

Heads-up: there's a pile of 8 (7 now ) Spectracom 8140 distribution amplifiers on eBay right now:
http://www.ebay.com/itm/Spectracom-8140-Frequency-Distribution-Amplifier-10Mhz-Input-Eight-Available-/221943556149?hash=item33acdde835:g:HRYAAOSwdvpWDWDb

One input, five outputs - four rear and one front.

[Shock]

This might be a dumb question but why the high bandwidth ? Don't most instruments add low pass filtering on their "REF" inputs ? I picked up an el cheapo chinese video distribution amp from fle-bay, ya it's 75 ohms but so far none of my HP gear seem to mind the slight impedance mismatch.

You mean the bandwidth of the CLC409 op amp in the Extron in particular? Well I'm no expert but it's a good indicator that signal fidelity issues at 10MHz will be non existent, if compared to say an op amp which has a lower bandwidth than the input signal, gain will be affected and since it's operating outside it's parameters it's going to exceed it's noise specifications. I can't tell you if this would make it totally unusable plugged into a reference input (as they aren't that fussy on signals) but if you want to use your distribution amp for higher frequencies you're going to hit a wall sooner or later.

About the impedance, well RF commonly uses 50 Ohm cabling and termination so we are just matching that. Mismatched impedance is going to affect the gain and unterminated it can cause reflections/superstitions of the source signal. Will it matter for a 10MHz ref input? Well guess it depends how clean your source and how fussy your ref input is.

[SoundTech-LG]

Heads-up: there's a pile of 8 (7 now ) Spectracom 8140 distribution amplifiers on eBay right now:
http://www.ebay.com/itm/Spectracom-8140-Frequency-Distribution-Amplifier-10Mhz-Input-Eight-Available-/221943556149?hash=item33acdde835:g:HRYAAOSwdvpWDWDb

One input, five outputs - four rear and one front.

but, don't forget, you'll need the Spectracom Line Taps, and/or the Versa Taps to fully utilize the system. as intended...  you can also modify it to remove the +12 Volts DC riding on the rear panel outputs.
http://spectracom.com/documents/instruction-manual-model-8140/attachment

[bson]

Good catch!  Wouldn't have noticed until I checked the output...  Bought a couple of taps to go with it.

[Gandalf_Sr]

Got my NTBW50AA now and have ordered a PSU; thinking I'll copy the mods that Steve has done for 1 pps etc.  One question though, is the RS232 'real' RS232 (i.e. does it need + and - signals) or is it TTL?  It says it complies with the RS232-E standard but that seems to be something to do with rise times and noise.  I can already do TTL RS232 but I'll need to buy a cable to do 'real' RS232.

[moya034]

If you want to put your frequency standard(s) and measurement ability to the test, the ARRL regularly sponsors a frequency measuring contest. http://www.arrl.org/frequency-measuring-test

[TheSteve]

The Nortel unit is real, old school RS232 from the DB9 on the front.

[bson]

Received the Spectracom 8140 and a couple of line taps, and it works perfectly.  My Thunderbolt outputs sinusoidal AC while the taps output sinusoidal DC.  The front BNC outputs a DC square wave that can be divided using the front buttons.  I'll be putting this to good use.

[Gandalf_Sr]

I may get a chance to test out my NTBW50AA today.  I bought it with the (perhaps slightly naive) idea that I could use the 10 MHz output as an external clock input to stuff like my N1996A and E4433B to get super accuracy.  Some research has shown that, unless the signal from the NTBW50AA plus distribution amp is better (lower phase noise and less jitter) then this is not a good idea so, until I do more research on that topic, I will use the 10 MHz output to check the calibration of my gear.

[Gandalf_Sr]

Getting a bit frustrated, I'm trying to make Lady Heather talk to my NTBW50AA.  I bought a USB-RS232 cable and it installs on my Windows 10 system as COM4.  I'm pretty sure the cable connections are good but all that happens when I start LH is it says 'NO COM1 SERIAL PORT DATA SEEN' - I'm now trying Windows 8 compatibility mode and am running LH as Admin.

I added a heather.cfg file with nothing but '/4' in it but I still get the message about COM1 when LH starts up, I also tried typing in '/4' at the command interface.  I messed with various setting for the port - current settings are 9600, 8 bit, no parity, 1 stop bit

Any suggestions anyone?

[EDIT1] It seems it's a Lady Heather problem.  I have found the serial port setting and it's 19,200,7,Odd,1, and I think XOn/XOff, with these settings I can connect to Port 4 and then when I type '1' it responds with "E-113>

[TheSteve]

Unless its actually in use you can do the easy solution and just change the usb serial port to com1 - then the default LH settings will work fine.

[Gandalf_Sr]

Unless its actually in use you can do the easy solution and just change the usb serial port to com1 - then the default LH settings will work fine.

Well duh!  That worked!  Thanks Steve
I believe the issue with Windows 10 is that they've changed the way 'My Documents' works and have some weird protection for where programs are allowed to access files from.  Steve's suggestion allowed LH to just use the defaults.

[TheSteve]

Unless its actually in use you can do the easy solution and just change the usb serial port to com1 - then the default LH settings will work fine.

Well duh!  That worked!  Thanks Steve
I believe the issue with Windows 10 is that they've changed the way 'My Documents' works and have some weird protection for where programs are allowed to access files from.  Steve's suggestion allowed LH to just use the defaults.

Excellent - lady Heather is a rather old school program, I run it on an old netbook running XP.
Btw your N1996A claims it can use PP2S for an external reference but it actually works with PPS only.

[Gandalf_Sr]

Did a test run with the antenna outside on a pole on my lawn just to make sure it was all working - it was, I'll post a picture tomorrow.  Now to do the proper installation but I need to do the modifications that Steve suggested to get 1 PPS out of the front panel.

[Lightages]

I have been running my BG7TBL / 2014-12-09 for quite a while now and it is working fine. I have been trying to get it working as a source for an NTP server using the instructions at: http://www.satsignal.eu/ntp/NTP-on-Windows-serial-port.html

I cannot get the receiver t change its settings to match the requirements to work at 4800 baud and use only $GPRMC sentences. I am using the u-center software but none of the settings I send take hold. With the default settings the NTP server software does not use the GPS as the clock.

Any suggestions?

[Gandalf_Sr]

OK, here's some pictures for y'all.  Does everything look OK from the data?

[Edit] OK, let me ask the question in a different way. Can anyone help me to interpret the data I'm seeing?  Given my interest in knowing that the Nortel box is giving me accurate timings, what do these indications tell me...

PPS^ -0.293456 ns
Osc^ 11.567843 ppt

Thanks in advance.

[TheSteve]

Did another small mod to my Nortel NTBW50AA that I've been meaning to do for a long time now. Instead of messing with the SMB connectors on the front I drilled a few holes on the back of the chassis and mounted BNC connectors for the GPS antenna in, 1 PPS and 10 MHz outputs. If you mount them on the back of the chassis you only need to drill through one layer of steel, use a step bit and the drilling is very easy. A few runs of coax cable run neatly under the PCB soldered to the SMB jacks or any other proper point on the PCB and you're done.
You can also see my power cable that runs through a rubber grommet installed in an existing chassis hole. The cable goes to a 2.1mm connector so I can use a 24 VDC wall adapter to power the unit.