From: on Wed, Feb 22 2006 7:01 pm

The other day I found myself needing a short gate time ~200 mhz
frequency counter for an automated test, and since I had an FPGA board
on hand I whipped one up quickly. Getting it reading and reporting to
my computer was the easy part.

Ah, the input stage....

I've got about 4dBm of RF into 50 ohms to play with - about a volt p-p
or a little more if it's high-Z. The output of the device under test
has a transformer and then a series cap to create an unbalanced output.

snip

If you want some good results, use a high-speed comparator
device. The Maxim MAX9010 family of comparators is fast
(5 nSec propagation delay) and it works into a TTL load.

At 1 V p-p you've got the input overdrive to insure fast
rise and fall times of the output. Note: 200 MHz (if that
is really what you wanted to write) has a period of 5 nSec
so even this very fast comparator is going to be pushed for
a good output. On the other hand it is STABLE and won't
"go into oscillation with no input."

http://www.maxim-ic.com

Samples are available. One in the family is in a SOT23
package, the rest smaller.


If ordering things, what would be a good default low supply voltage
HF/VHF gain component to have on hand? I seem to recall lots of
last-millenium ham designs using the MC1350P video IF amp, but what
would make sense today?

The MC1350P is second-sourced by Lansdale. It is still a very
good differential in/out building block with good AGC control.
The MC1349P is a pin/function equivalent and can be ordered from
Dieter Gentzow's PartsAndKits.com at 3 for $3. Same place is a
good source of small-quantity toroidal cores. Both ICs are
called out with 12 VDC supplies but they will work down to
9 VDC with little degredation. Open-collector outputs, constant
5 KOhm || 5 pFd input, AGC control down to 60 db (if needed).