If you're going to go for a universal counter, watch out for the HP 5315/5316 units. They're pretty good, don't take a lot of space and are very quiet and reliable.
Let me throw the Philips PM6685 (one channel) and PM6680 (two channels) in.
![Smiley :)](https://www.eevblog.com/forum/Smileys/default/smiley.gif)
I have them both and do really like (and therefore use) them
1).
Some pros and cons (the selection is completely subjective and therefore incomplete):
+ They measure frequency to 300MHz/225MHz (100MHz on the 2nd channel) and give you 10 Digits at 2 measurements/sec.
+ GHz-input (several different options) available as options -there are Polish and Chinese vendors offering 3rd party kits at affordable prices that have overall good reputation (don't have one myself).
+ They have no potentiometer on their user interface as it is fully controlled via push buttons.
neutral to - They can be fully controlled over GPIB if equipped with (the PM6680 more often than the PM6685).
edit: According to their data sheet the HP 5315/5316 are generally equipped with GPIB.
- A downside -the standard oscillator and the next grade, the TCXO are too poor for taking advantage of the 10 digits resolution, but:
neutral The PM6685/6680-family is equipped with a 10MHz reference input. So one can take advantage of a GPSDO..
![Wink ;)](https://www.eevblog.com/forum/Smileys/default/wink.gif)
edit: I just noticed the HP 5316 also has a refence input..
+ Refitting a selfmade OCXO-module also isn't too complicated because these counters simply offer oven supply and reference input on a pin header and the service manual is available.
+ The PM6680 compares well to Agilent 53131A -in some aspects it is better -so TEA isn't really triggering me to get a 53131A -and the 53131A goes for more than the PM6680 in general.
- OK, looking at the form factor the goal goes to the HP 5315/5316 as the PM6685/6680 is only two rack units high but 395 mm (15.6 in) deep.
Fluke sold the PM6685 under its name and the PM6680 as PM6680B (haven't seen differences between it and the Philips PM6680) and an improved version with 11 digits resolution -the PM6681.
Footnote:
1) -BTW, a PM6681 will hopefully be delivered (undamaged! -fingers crossed) to me in the next week.
I'm curious how they managed to give the user 11 digits. As far as I know they use the same 10 digits display like in the PM6680/B.
![Huh? ???](https://www.eevblog.com/forum/Smileys/default/huh.gif)
Perhaps it'll give the 11 digits resolution only over GPIB -would be OK for me because I want to use it to make long time measurements using a raspberry pi as command station.