On Mon, 29 May 2017 17:29:44 +1000, Clifford Heath
wrote:
I don't know what frequency the PIC counter input is capable of,
but I know that the AVR counter is clocked; so you can only count
at half the CPU clock frequency. Bah, humbug.
The clock crystal is 4MHz on the old version. I can't read the
numbers on the schematic of the new version. That doesn't look very
promising for measuring 60MHz inputs or even with /4 at 15MHZ.
It also shows that the gates of the DG MOSFET are
NOT tied together.
The units I have have both pairs of protection diodes, and the inputs
are joined only at the connector. I cut the trace and soldered a bit
of co-ax onto the prescaler input capacitor.
Oh swell. So the PCB wiring might not follow the schematic. I
suppose it doesn't matter since the DG MOSFET seems to be badly biased
anyway.
I was having nightmares last night from thinking about this counter.
Maybe I should give up while I'm still sane?
I don't have a good RF source (yet - currently building, see
https://github.com/cjheath/AD9851LCD) so I can't evaluate the
sensitivity.
Before you reinvent the wheel, there are AD9851 based DDS generators
available on eBay.
http://www.ebay.com/sch/i.html?_nkw=dds+generator+ad9851
along with the associated LCD display:
http://www.ebay.com/itm/PIC16f-Controller-for-the-AD9851-DDS-Signal-Generator-Module-/182593721953
However, those only go up to about 70MHz and the output looks
distorted above 30MHz. If you're going to test the counter all the
way to its rated maximum frequency (2.4GHz), you're going to need a
better generator. DDS has benefits for a function generator and
arbitrary waveform generator, but is limited to lower frequencies.
This looks interesting (and tempting):
http://www.ebay.com/itm/ADF4350-v4-0-137-5MHZ-4-4GHZ-OLED-display-Signal-generator-RF-signal-source-12v-/262688224985
137.5MHz to 4.4GHz signal generator in 10KHz steps. Looks ok to about
1GHz, but drops in output and increases in sidebands at higher
frequencies. Looks like the same board, but in a shielded box:
http://www.ebay.com/itm/137-5MHZ-to-4400MHZ-Signal-generator-frequency-generator-RF-signal-source-dc-12v-/271838837908
Or maybe this thing:
http://www.ebay.com/itm/0-5Mhz-470Mhz-RF-Signal-Generator-Meter-Tester-For-FM-Radio-walkie-talkie-debug-/172598060649
Or maybe something computah controlled via USB:
http://www.ebay.com/itm/RF-Signal-Generator-35MHz-to-4-4GHz-via-USB-16dBm-Plus-Features-2000-units-sold-/201929990411
Or maybe a real RF generator from HP, TEK, Fluke or others that can
actually be calibrated and trusted. This is the cheapest HP I could
find:
http://www.ebay.com/itm/Hewlett-Packard-hp-8656A-Signal-Generator-1-990MHz-rf-signal-generator-04-/252950700229
I have an HP 8656A but prefer to use an HP 8540B. Top right:
http://802.11junk.com/jeffl/pics/home/slides/test-equip-mess.html
--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060
http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558