#### DP501 Digital Prescaler

I have one of these (and in mint condition, probably because nobody ever used it), and have not been able to find a manual anywhere, so it's hard to answer this burning question:

Why on EARTH does it divide by 16? how is this good for anybody in practice? every other prescaler on earth (including the ones in other Tek counters) provides effective divide by 10 results so the data is instantly usable, but this item does not. Is there some mystical way it fixes that by a rear panel connection I can't see (thanks to no manual)?

I have tested it, and YES, it does in fact divide by 16, and mine worked up the 1.6Ghz with no trouble.
what I can't figure out is why it works this way with other Tek counters, like my DC503, which has a GHz indicator, but makes no special use of the DP501. I feel like there is an answer out there, I am just not sure where it is hiding in all the Tek docs. Are there some magical backplane connections that make this work correctly? I would really like to know, the catalog listing is totally unhelpful, and seems to imply this has a solution, but doesn't say how.

any help appreciated,
walter (walter2 -at- sphere.bc.ca)
sphere research corp.

On Mon, Jul 15, 2019 at 12:48 AM, walter shawlee wrote:

Why on EARTH does it divide by 16?
Prescalers like these are built using flip-flops that each divide by two. With 3 stages, you divide by 2^3 (8), with 4 stages, you divide by 2^4 (16), *unless* you use a mechanism to detect a special count value, like 10, and acting on that. You need much faster logic to detect such an intermediate value and reset the chain "at 10":
At the time, flip-flops were barely fast enough to keep up at 1.3 to 1.6 GHz, so resetting at intermediate values was out of the question. Bear in mind that the input signal had to ripple through the flip-flops, before detection/decoding of an intermediate count could be done, which would not happen until after the ripple-through was done.
More modern counters also have (internal) prescalers dividing by integer powers of 2, like the (3 GHz - 12 GHz) prescalers for the well-known HP 53131/53132 family of counters. The firmware in the counter corrects the value to be displayed.
Not much difference, just newer, faster technology.

Raymond

On Mon, Jul 15, 2019 at 12:48 AM, walter shawlee wrote:

other Tek counters, like my DC503, which has a GHz indicator,
AFAIK, neither the DC503 nor the DC503A counters (100/125 MHz AFAIK) has a GHz indicator. They wouldn't be aware of a prescaler present, unless through special backplane connections as you suggest, which could pull all kinds of tricks, even changing the time base frequency "in prescaled mode only" by an equivalent factor. Ugly but it would work...

Just guessing and mentioning possible solutions because I have no docs nor a DC503(A).

Raymond

On Mon, Jul 15, 2019 at 01:17 AM, Raymond Domp Frank wrote:

even changing the time base frequency "in prescaled mode only" by an
equivalent factor. Ugly but it would work...
The DP501 specs on Tekwiki state that "In the Prescaler mode, the DP501 divides the input signal by 16 and causes the associated counter's display to be multiplied by 16", which definitely points to my suggested solution. A simple logic signal across from the prescaler to the counter would take care of this switching-in of a divide-by-16 counter into the time base chain. I can't imagine the User Manual and/or Service Manual *not* mentioning this.

Raymond

J Mcvein

Well, I have a DC509/5009 counter and a DP501 prescaler set.
There is a backplane connection to enable the counter to recognize
the extender.  While there may be the capability of a DC503 touse a prescaler, the triggering/threshold on said counter is crap.The device is said to work marginally with a DC504.
I do have a manual for DC501, it was from Qservice Greece.  The setupdoes work quite well, and the upshot might be that the DP501 is a
one trick pony.
JimMc

On Sunday, July 14, 2019, 3:48:11 PM PDT, walter shawlee <@walter2> wrote:

I have one of these (and in mint condition, probably because nobody ever used it), and have not been able to find a manual anywhere, so it's hard to answer this burning question:

Why on EARTH does it divide by 16?  how is this good for anybody in practice?  every other prescaler on earth (including the ones in other Tek counters) provides effective divide by 10 results so the data is instantly usable, but this item does not.  Is there some mystical way it fixes that by a rear panel connection I can't see (thanks to no manual)?

I have tested it, and YES, it does in fact divide by 16, and mine worked up the 1.6Ghz with no trouble.
what I can't figure out is why it works this way with other Tek counters, like my DC503, which has a GHz indicator, but makes no special use of the DP501.  I feel like there is an answer out there, I am just not sure where it is hiding in all the Tek docs. Are there some magical backplane connections that make this work correctly? I would really like to know, the catalog listing is totally unhelpful, and seems to imply this has a solution, but doesn't say how.

any help appreciated,
walter (walter2 -at- sphere.bc.ca)
sphere research corp.