[time-nuts] Extron 3 80 video distribution amplifier

Dave Brown tractorb at ihug.co.nz
Thu Sep 7 00:35:06 EDT 2006


I acquired a similar type of unit (sold as a VGA splitter) recently 
for exactly the same purpose-it has three analog channels and a TTL 
sync channel.
I have not yet done any tests on this box but it has a claimed b/w of 
250 MHz in each of the video channels.
 Interestingly the video amp is actually a 4 channel device (not a 
687J, sorry!) and one section is unused with input and output 
grounded. So some scope for soldering iron work to get to use that 
fourth section.

Each of the video amps drives four outputs via individual series 75 
ohm resistors - the inputs are each shunt terminated with 75 ohms but 
with no loop/thru options. No gain set options either-the amp 
configuration looks similar to a MAX497 etc with fixed x2 gain.
The sync channel uses an LS244 so probably not of much use/interest.
Will report further after testing.

DaveB, NZ


----- Original Message ----- 
From: "Didier Juges" <didier at cox.net>
To: "5_Time Nuts" <time-nuts at febo.com>
Sent: Thursday, September 07, 2006 3:18 PM
Subject: [time-nuts] Extron 3 80 video distribution amplifier


> Hello fellows Time Nuts,
>
> Following a question of mine here a few weeks ago about using a 
> video
> distribution amplifier for frequency reference distribution, and 
> lots of
> good advice I got in response, I just got one of those distribution
> amplifiers from eBay and there are good news. The box is very 
> sturdy, if
> not very RF proof, and all the electronics of the unit itself fits 
> on a
> PWB that is mounted along the rear panel, the rest of the box (about 
> 85%
> of it) is EMPTY, with many mounting studs on the top and bottom 
> panels,
> a hacker's dream.
>
> The box has plenty of room for a GPS receiver, an HP 10811 OCXO, a
> microprocessor board and a display, if you see where I am going.
>
> Of course, the original wall-wart will not power the new guts, but a
> cheap laptop type switcher from www.allelectronics.com will do the 
> job
> nicely for few $. I need an 18 or 20V unit, then I will put a small
> switching step down regulator for the GPS receiver, it would be 
> wasteful
> to use a linear regulator to step from 18-20V down to 5V at 300-400 
> mA
> (I have used the LT1375HV for that in many projects).
>
> Since I hate making enclosures from scratch for my projects (the 
> least
> fun part in my opinion), this one will be well taken care of.
>
> If you are interested in using this amplifier, here is some more 
> info
> than is available on the Extron web site.
>
> The Extron 3 80 has 4 inputs (R, G, B and SYNC) and each drives 3 
> normal
> outputs and a LOOP output. The R-G-B channels are analog and the 
> SYNC
> input drives TTL gates, so depending on your application, it may or 
> may
> not be suitable for time or frequency distribution. Each input has a
> corresponding LOOP output, which is simply in parallel with the 
> input,
> for looping through another device. You could use the LOOP outputs 
> to
> loop a single 10 MHz signal through all 3 inputs and have 9 outputs
> right off with no modification (just put the switch to LOOP and put 
> a
> termination on the last LOOP output to terminate the line) and low 
> skew.
>
> I need at least 5 outputs at the moment, so 9 will suffice for a 
> while
> for my purpose. Also, I only need it for frequency reference, not 
> for
> timing, so delay is not a big concern to me at the moment (when I
> graduate to full-fledged [time-nut], this may change :-) It would 
> not be
> too hard to modify the unit internally for one input and 16 outputs 
> all
> in sync (give or take a nS or two), and 3 spare connectors.
>
> The delay between each input and any of the corresponding outputs is
> about 10-11 nS (measured with a sine wave input from my HP 8657B on 
> a
> TDS210 60 MHz scope, I will use the HP 5334B for more accurate 
> reading
> later.) The delay between each input and the corresponding LOOP 
> output
> is 1-2 nS.
>
> There is a switch labeled 75 ohm/LOOP which simply makes the R-G-B
> inputs high-Z in the LOOP mode, 75 ohms otherwise.
>
> There is another switch that adjusts the gain of the R-G-B channels 
> to
> 1:1 or 1:0.7. In addition, each analog channel has an adjustment
> potentiometer inside that allows to adjust the gain from 0-120% of 
> rated
> (assuming 50 ohm loads on the outputs). Each R-G-B channel also has 
> an
> internal jumper, I have not determined what it does yet. A schematic
> would be handy.
>
> The wall wart is a 9VDC unit, the amplifier has an internal negative
> voltage generator and two regulators to drive the video amplifiers 
> which
> operate from +/- 5V.
>
> I do not have the schematic, and it will be hard to pull because of 
> all
> the connectors that clutter the PWB. If anyone has the schematic, 
> that
> would be appreciated. Note that the PWB is common with another unit 
> that
> has 6 outputs (and no LOOP output) for each input, the PWB is
> differently populated. I guess either schematic would do.
>
> The video amps are labeled 687J and do not have identifiable
> manufacturer label. I could not find a link to a spec sheet. There 
> also,
> any help would be appreciated.
>
> Didier KO4BB
>
>
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>
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