Re: [time-nuts] HP 5087A Input Doubler and 10 MHz Ampifiers
"NE8S" ne8s@earthlink.net wrote:
I am in need of the following Opt PCB's for the HP 5087A:
...
Qty. 11 5087-60012 (10 MHz Amplfiers)
Good luck. I like to a have some more of these as well.
I have considered doing a run of 60012 boards. This would be
straightforward except for one thing: I have been unable to find any spec
for the transformers. That part would have be to characterized.
Note that you can convert 5MHz boards to 10MHz by changing a couple of
discrete component values.
-ch
There is nothing special about the 5087A's amplifier cards. The 5087A
design is not especially quiet; in fact, it will degrade the broadband floor
of a Thunderbolt by a good 7 or 8 dB from what I have seen.
I'd say grab some PCB prototyping stock and a Dremel tool, and surf through
Bruce's notes and references at
http://www.ko4bb.com/~bruce/IsolationAmplifiers.html for some ideas.
-- john, KE5FX
-----Original Message-----
From: time-nuts-bounces@febo.com [mailto:time-nuts-bounces@febo.com]On
Behalf Of christopher hoover
Sent: Monday, July 07, 2008 6:55 PM
To: time-nuts@febo.com
Subject: Re: [time-nuts] HP 5087A Input Doubler and 10 MHz Ampifiers
"NE8S" ne8s@earthlink.net wrote:
I am in need of the following Opt PCB's for the HP 5087A:
....
Qty. 11 5087-60012 (10 MHz Amplfiers)
Good luck. I like to a have some more of these as well.
I have considered doing a run of 60012 boards. This would be
straightforward except for one thing: I have been unable to find any spec
for the transformers. That part would have be to characterized.
Note that you can convert 5MHz boards to 10MHz by changing a couple of
discrete component values.
-ch
John Miles wrote:
There is nothing special about the 5087A's amplifier cards. The 5087A
design is not especially quiet; in fact, it will degrade the broadband floor
of a Thunderbolt by a good 7 or 8 dB from what I have seen.
I'd say grab some PCB prototyping stock and a Dremel tool, and surf through
Bruce's notes and references at
http://www.ko4bb.com/~bruce/IsolationAmplifiers.html for some ideas.
-- john, KE5FX
Just watch for the odd error in those references.
eg in the first reference (.../498.pdf) the captions for figure 2 and
figure 3 should be swapped.
If anyone wants to try it, I have an even quieter, lower distortion 3
transistor isolation amplifier design that runs from a 12V supply.
I'll add it to that page in the next few days. It has a 50 ohm input
impedance and can be driven from a splitter which is in turn driven by
another such amplifier to form a high reverse isolation and channel to
channel isolation, low noise distribution amplifier.
Whatever you do don't copy JPL's isolation amplifier designs they are
relatively noisy particularly in the flicker noise region.
Bruce
Just watch for the odd error in those references.
eg in the first reference (.../498.pdf) the captions for figure 2 and
figure 3 should be swapped.
If anyone wants to try it, I have an even quieter, lower distortion 3
transistor isolation amplifier design that runs from a 12V supply.
I'll add it to that page in the next few days. It has a 50 ohm input
impedance and can be driven from a splitter which is in turn driven by
another such amplifier to form a high reverse isolation and channel to
channel isolation, low noise distribution amplifier.
Certainly, put it up there -- that's a handy collection of ideas. I'd like
to add a couple of low-noise outputs to my 5087A at some point, actually.
There's a lot of empty space on the front panel that bugs me.
-- john, KE5FX
John Miles wrote:
Just watch for the odd error in those references.
eg in the first reference (.../498.pdf) the captions for figure 2 and
figure 3 should be swapped.
If anyone wants to try it, I have an even quieter, lower distortion 3
transistor isolation amplifier design that runs from a 12V supply.
I'll add it to that page in the next few days. It has a 50 ohm input
impedance and can be driven from a splitter which is in turn driven by
another such amplifier to form a high reverse isolation and channel to
channel isolation, low noise distribution amplifier.
Certainly, put it up there -- that's a handy collection of ideas. I'd like
to add a couple of low-noise outputs to my 5087A at some point, actually.
There's a lot of empty space on the front panel that bugs me.
-- john, KE5FX
John
Will add the general configuration shortly and follow up with a 5087
specific version that is tailored for the 5087 +18V supply.
Have been looking at the 5087 amplifier schematics and it appears that
most of the noise is due to the fact that the various output amplifiers
have a gain of somewhere around 10x or so judging by the waveform
amplitudes given on the schematic. The amplifiers have a fixed gain (for
a given load) and large amplitude inputs are accommodated by attenuating
them. Lower noise for high amplitude inputs is achieved if the amplifier
gain is adjusted to suit the input signal level rather than attenuating
the input to suit the amplifier.
You will also need to change the 5087A input amplifier - although its a
relatively low noise emitter follower it wont drive a 50 ohm load or
several in parallel especially with a +13dB input signal.
For those who like to use wide bandwidth opamps I'll indicate how to
achieve a phase noise floor within 6-12 dB of a low noise discrete design.
As NIST have shown there is no need to use particularly exotic
transistors for 10MHz distribution amplifiers.
Bruce