Products > Test Equipment
Hantek HDG2002B AWG: 5Mhz or 100MHz? Let's see!
idpromnut:
--- Quote from: Cyber7 on September 24, 2014, 12:40:50 am ---Do you have a better pic of the U25 area, or happen to make note of the part #?
--- End quote ---
Nuts, you're right! I pulled apart my unit just now to check and indeed, I do have a SO-8 in U25, and yes, it is a LMX5080.
Cyber7:
:-+ Many thanks for the sanity check! :-+
It's gonna be a PITA to get an LMX5080 if mine is missing... |O
Sadly the MB510 if a 5v part and Vcc is 3.3v. Worst case, the Ti campus is only 15 miles away; I could go up and ask to see someone in their RF comp section and beg/horse trade for old stock samples...LOL :P
marabut:
idpromnut, I've checked HF counter exactly the same way fremen67 did:
--- Quote ---I tried to connect one channel set to the max frequency (100Mhz Sine) to the HF counter directly on the PCB and guess what... it worked! It seems that everything, except the jack, is already on board for the HF counter to work :-DD
--- End quote ---
Thank you very much for checking U25 :-+.
Now I know what to lok for, at least.
Cyber7, I hope you will have more luck than me. I can't find LMX5080 anywhere near my location, even eBay search returned no result (not a single one, literally!). On the other forum, somebody suggested to look for old mobile phone / Tsat tuner boards where LMX's were used. I will ask on HAM radio forum as well. Maybe they have some...
By the way, I have tried to measure 10MHz reference output (using LF counter channel). I've expected exactly 10 000 000 as the same clock is used to control gate circuit, but result was somewhere near and changed with almost every read... Counter design flaw? Gate time generated by software? :wtf:
Strange behavior, anyway.
idpromnut:
--- Quote from: marabut on September 24, 2014, 07:41:37 am ---By the way, I have tried to measure 10MHz reference output (using LF counter channel). I've expected exactly 10 000 000 as the same clock is used to control gate circuit, but result was somewhere near and changed with almost every read... Counter design flaw? Gate time generated by software? :wtf:
Strange behavior, anyway.
--- End quote ---
It definitely feels like a software-based counter. After reading this, I did a couple more tests with the HF counter, and noticed that the HF counter seems to have sub-par termination. Testing with a 10MHz 5Vpp sine wave, we get this when the FG is connected to the LF counter (HDG is reading 9.882MHz):
And this when connected to the HF counter (HDG is reading 9.879MHz):
With a 15MHz 5Vpp sine wave, we get this on the LF counter (HDG is reading 14.762MHz):
And this when connected to the HF counter (HDG is reading 14.761MHz):
marabut:
I think you shouldn't drive HF counter input with anything above ~1Vpp (unless you want to fry input circuit components >:D )
From PCB traces (take a look at the picture I've posted) you can see that signal is routed from input connector through small capacitor to two antiparallel connected diodes D9 (signal limiter) and then through another capacitor to LMX input.
LMX5080 can work with maximum signal +4dBm (according to datasheet) which translates to 1Vpp. Even "Absolute maximum ratings" say that voltage on *any* pin cannot exceed Vcc+0.3V. I don't know actual Vcc but it's more safe to assume that Vcc is 3V rather than 5V.
So, feeding it with 5V signal doesn't serve it well ;)
It is possible that sinewave distortion you see is caused by limiter circuit. With smaller (<1Vpp) signal waveform will be better, I guess.
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