Do you need the accuracy of the frequency standard? Why not just buy a
little 4MHz CMOS crystal oscillator?

If jitter and accuracy were important I'd either (hobby use) build a VXCO
with an 8MHz crystal referenced to 2MHz from the standard or (for a customer
design) buy an integrated 4MHz VXCO and reference it to 2MHz from the
standard. In either case I'd use the phase comparator from a 74HC4046 or an
exclusive OR gate. You'll be using a divide-by 5 which can be had from a
74HC390 if they're still available, and a divide-by 2 or 4, which can be had
from just about anything -- including the same 74HC390 if your hookup is a
little perverse. All the logic _could_ be done on a PAL, of course.

Come to think of it if absolute accuracy is important but jitter isn't you
can just use the oscillator from the '4046 as well, with the same division
scheme.

--------------------------------------
Tim Wescott
Wescott Design Services
http://www.wescottdesign.com


"Mike W" wrote in message
...
I have a need to produce an accurate 4Mhz 50% dutycycle TTL squarewave
to use as a timebase.

I have a 10Mhz IQD frequency standard of suitable accuracy. How can I
divide this to produce the 50% duty cycle 4Mhz signal?. Is it even
possible with logic alone?. I can see how to mix with either 6Mhz or
14Mhz, but this then detracts from the required accuracy.

atb Mikw

"Mike W" wrote in message
...
I have a need to produce an accurate 4Mhz 50% dutycycle
TTL squarewave to use as a timebase.

I have a 10Mhz IQD frequency standard of suitable accuracy.
How can I divide this to produce the 50% duty cycle 4Mhz
signal?. Is it even possible with logic alone?. I can
see how to mix with either 6Mhz or 14Mhz, but this then
detracts from the required accuracy.


I'd be tempted to use a PAL chip. It is possible to make a multiply by 4
and then divide by 10 in the same chip, which would make the total parts
required to get the 4 MHz 50% Sq Wave your original 10 MHz input and a
single chip.


Jim Pennell
N6BIU

On Fri, 20 Feb 2004 03:08:14 GMT, "Jim Pennell"
wrote:



I'd be tempted to use a PAL chip. It is possible to make a multiply by 4
and then divide by 10 in the same chip, which would make the total parts
required to get the 4 MHz 50% Sq Wave your original 10 MHz input and a
single chip.


Mice one Jim.
1. buy your PAL programmer
2. buy your PAL
3. learn how to obtain the required function
4. burn the PAL and discover it does'nt work
5. while patience lasts go to 2. wend
6. revert to PLL

On Fri, 20 Feb 2004 09:56:22 GMT, (Mike W) wrote:

On Fri, 20 Feb 2004 03:08:14 GMT, "Jim Pennell"
wrote:



I'd be tempted to use a PAL chip. It is possible to make a multiply by 4
and then divide by 10 in the same chip, which would make the total parts
required to get the 4 MHz 50% Sq Wave your original 10 MHz input and a
single chip.


Mice one Jim.
1. buy your PAL programmer
2. buy your PAL
3. learn how to obtain the required function
4. burn the PAL and discover it does'nt work
5. while patience lasts go to 2. wend
6. revert to PLL

I could do the same analysis for a PLL - it isn't a two minute job.

Do you have a problem with an XOR chip and a 74(xx)90?

On Fri, 20 Feb 2004 09:56:22 GMT, (Mike W) wrote:



Mice one Jim.
1. buy your PAL programmer
2. buy your PAL
3. learn how to obtain the required function
4. burn the PAL and discover it does'nt work
5. while patience lasts go to 2. wend
6. revert to PLL


Well, true... Happens I have access to that sort of thing, but I do see
your point.

Another approach might be to divide by 5 and then you can double twice
with a couple of chips, and then divide by 2 to get the 50% duty cycle.

A PLL system works, but for something this simple a couple of generic glue
logic IC's will serve the purpose.

Let me see, it'd require a 7490, a hex inverter for some delay in the
multiplier, and a 7400 nand. If memory serves, that ought to do it.


Jim Pennell
N6BIU

Anyone care to nominate an RF mixer chip for 100Mhz that's readily
available in the UK?
--

The BBC: Licensed at public expense to spread lies.

Paul Burridge wrote in message
...

Anyone care to nominate an RF mixer chip for 100Mhz that's readily
available in the UK?
--

The BBC: Licensed at public expense to spread lies.

LM1496

On Sat, 21 Feb 2004 12:28:13 +0000, Paul Burridge
wrote:


Anyone care to nominate an RF mixer chip for 100Mhz that's readily
available in the UK?


give 'em a call for free samples...


EUROPE
Hittite Microwave Europe Ltd
Sales and Applications
4.1 Intec Wade Road,
Basingstoke Hampshire,
RG24 8NE,
United Kingdom

E-Mail:
Phone: +44 1-256-817-000
Fax: +44 1-256-817-111













[]



Remove "HeadFromButt", before replying by email.

Paul Burridge wrote:
Anyone care to nominate an RF mixer chip for 100Mhz that's readily
available in the UK?

What sort of performance is required? Diode mixers are easy to obtain
and have good IMD characteristics. The impedances on the ports need to
be properly matched.

Leon
--
Leon Heller, G1HSM
Email:
My low-cost Philips LPC210x ARM development system:
http://www.geocities.com/leon_heller/lpc2104.html

On Sat, 21 Feb 2004 18:22:44 +0000, Leon Heller
wrote:



Paul Burridge wrote:
Anyone care to nominate an RF mixer chip for 100Mhz that's readily
available in the UK?

What sort of performance is required?

"Good." :-)

Diode mixers are easy to obtain
and have good IMD characteristics. The impedances on the ports need to
be properly matched.

What - the sort of crossed diode config one often sees in the ham
design books? Do you think I might as well just make one up from
discretes? I'm basically just trying to combine 60Mhz with 20Mhz to
end up with the difference frequency in this case. JJ suggested a
chip, but looking at the data sheet, it seemed to be designed more as
a modulator than a mixer. Let's not get into an argument over
semantics but y'all know what I mean, I'm sure.

BTW, thanks for a good steer with the Pulsonix suggestion, Leon. I'm
making good progress getting to grips with it.
--

The BBC: Licensed at public expense to spread lies.