been referring to the 339a as an oscillator... meant analyzer. The notch is on the A3 pcb...Fundemental Rejection Circuit. aka Notch Filter. OK?
Using this portion and/or also modifying the variable passive twin-t to run with the twin-T active circuit are projects for me to think about. Thx-RNMarsh
Using this portion and/or also modifying the variable passive twin-t to run with the twin-T active circuit are projects for me to think about. Thx-RNMarsh
I was looking at the K-H4400A circuit which uses a bridge-T oscillator which is a notch according to Circuit Description in its manual. That gave me the idea in the first place of using the notch in the spare 339a with the QA400 or other ADC.
But I'm not going to use the K-H4400A for that. I am going to see if it will go lower in THD than the modified 339a because of the trouble getting lowest thd at all frequencies. As you said, you need another wafer to trim thd levels at all freq. The K-H might be better in this respect. I got one a few days ago off eBay for $200. Waiting for it now.
Thx-RNMarsh
But I'm not going to use the K-H4400A for that. I am going to see if it will go lower in THD than the modified 339a because of the trouble getting lowest thd at all frequencies. As you said, you need another wafer to trim thd levels at all freq. The K-H might be better in this respect. I got one a few days ago off eBay for $200. Waiting for it now.
Thx-RNMarsh
Hi Rick,
The mod to the passive twin t would be an easier task. It would be just a matter of lifting the T grounds and inserting the output of the positive feedback amplifier and adding an output buffer.
It's been a while since I looked at the 4400A. If they use a Jfet for control element then you will have the same trouble.
I havent found the limit to be the jFET yet. I started with reaching the limit with an A-Prec model One; then I am now at the low end of the the ShibaSoku. Never changed the jFET... did try but went back to original now. I can get the 339a oscillator to -125-ish. Not sure due to noise there.... need the ADC to look at it now and seperate the noise from the harmonics.
I think the Passive filter I have already (B&K 1607) will be the best approach, also. The box is plenty big to house active circuit AND it is continuously variable over a wide range. Anyone else have such a pasive filter or going to get one asap?
Thx- Richard
I think the Passive filter I have already (B&K 1607) will be the best approach, also. The box is plenty big to house active circuit AND it is continuously variable over a wide range. Anyone else have such a pasive filter or going to get one asap?
Thx- Richard
I havent found the limit to be the jFET yet. I started with reaching the limit with an A-Prec model One; then I am now at the low end of the the ShibaSoku. Never changed the jFET... did try but went back to original now. I can get the 339a oscillator to -125-ish. Not sure due to noise there.... need the ADC to look at it now and seperate the noise from the harmonics.
I think the Passive filter I have already (B&K 1607) will be the best approach, also. The box is plenty big to house active circuit AND it is continuously variable over a wide range. Anyone else have such a pasive filter or going to get one asap?
Thx- Richard
I don't know. If I type Twin T into the Ebay search all I get is car parts coming up.
B&K 1607 is no help either.
@Richard -- Victor has used an old but good technique to verify levels of harmonics, which is to use a second generator to make a marker with frequency very close to the harmonic of interest, attenuated by a known amount relative to the fundamental under test, say -120dB, and mixed with the fundamental.
Then despite any gain error -- filter, ADC, software, etc -- the level of the harmonic relative to the marker signal will give accurate results, so long as they are close in frequency (if being in the center of an FFT bin is critical, this should be checked/adjusted). This should eliminate a lot of uncertainty about levels. Any old generator will do, even a function generator, since it's harmonics will have no affect on the fundamental being examined.
Just throwing this out because I know you care about the real levels being seen in plots.
Then despite any gain error -- filter, ADC, software, etc -- the level of the harmonic relative to the marker signal will give accurate results, so long as they are close in frequency (if being in the center of an FFT bin is critical, this should be checked/adjusted). This should eliminate a lot of uncertainty about levels. Any old generator will do, even a function generator, since it's harmonics will have no affect on the fundamental being examined.
Just throwing this out because I know you care about the real levels being seen in plots.
Thank you for the reminder. I saw his scheme and have a mental note about it. Very nice idea as a cal for reality check. Just keep pushing down the distortion source and measurement levels.... I think 10 more DB's and I'll be happy with a close to -140 Real number that can be duplicated and used easily (well sort of easily). But thats coming harder and harder and a little slower now. But looks attainable. Thank you -
OT so forgive me. I've been following the various oscillator threads passively (except when I fixed my 339A) but seeing the "Morrey" name rang a bell - I wondered if it could be my elementary-high school friend Walt and looked up the ref'd article on his Heathkit mods and indeed it is him - a fun side-effect of following the thread. I last saw him at our 45th HS reunion ... probably will again in 2014, have corresponded infrequently.
OK ... back to your regular discussion.
OK ... back to your regular discussion.
Nice to find old friends by almost accident....
Just to add a note, the 239 mods to the IG-18 turned into a 339 mod and works quite well. Info on my webpage at www.moorepage.net
Just to add a note, the 239 mods to the IG-18 turned into a 339 mod and works quite well. Info on my webpage at www.moorepage.net
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