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| Review: Hantek DDS 3X25. Anyone own one? |
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| saturation:
Here's a sample of the Hantek output, yellow and the sync output, blue, with the Hantek programmed for 12MHz. They are general 'clean' but off, so its not possible to sync both signals together onto the 1052e with the standard triggers, which uses one channel to trigger both channels, or even the ext sync input. However, if you set the Rigol to 'alternate' mode, it will trigger each channel separately. You can now estimate the difference in the frequency between each channel. |
| alm:
--- Quote from: saturation on March 16, 2011, 12:48:37 am ---When composite was popular, I'd suspect 'high frequency ' was at a lower range compared to today. --- End quote --- Yep, it was probably only up to 500MHz or so those days, although I don't see any inherent reason why they wouldn't work above that (until lead inductance becomes an issue). I wasn't suggesting using them in new designs (they're pretty much obsolete), but they're definitely better for high frequencies than most other common through-hole types (does anyone even make SMD carbon composition resistors?), like metal film and carbon film. --- Quote from: saturation on March 16, 2011, 12:48:37 am ---http://books.google.com/books?id=zpTnMsiUkmwC&pg=PA2&lpg=PA2&dq=carbon+composition+resistor+frequencies&source=bl&ots=B4EZgRvC7Y&sig=qJiDRN3VxUrlkxH2Rb2aQ5kBtLU&hl=en&ei=PASATfuTEsSM0QGujIX7Dw&sa=X&oi=book_result&ct=result&resnum=10&ved=0CFgQ6AEwCQ#v=onepage&q=carbon%20composition%20resistor%20frequencies&f=false --- End quote --- You can't view this page, viewing limit has been reached. What did it say? |
| saturation:
Hi alm, sorry the link didn't work. I've copied it here. Now we can easily get 100 MHz for home labs, and 500 MHz is not outrageously priced. When perusing various references, the word 'excellent high frequency response' and 'poor response' for carbon composition resistors are used by almost an even split of different EE articles [ not hobbyist level links] and seem contradictory. You'll notice that on a google search. But the authoritative references like Fink's EE Handbook and most top references do us a favor and publish relative response curves. Here are 2 books with viewable pages online: http://www.amazon.com/Circuit-Design-Second-Christopher-Bowick/dp/0750685182/ref=cm_cr_pr_product_top http://www.amazon.com/Reference-Data-Engineers-Ninth-Communications/dp/0750672919/ref=sr_1_1?ie=UTF8&qid=1300319322&sr=8-1 Maybe the contradictory opinion on carbon composition resistors is that for high frequency use, its mostly just for historical interest as its just not used for that purpose today. --- Quote from: alm on March 16, 2011, 09:31:36 pm --- --- Quote from: saturation on March 16, 2011, 12:48:37 am ---When composite was popular, I'd suspect 'high frequency ' was at a lower range compared to today. --- End quote --- Yep, it was probably only up to 500MHz or so those days, although I don't see any inherent reason why they wouldn't work above that (until lead inductance becomes an issue). I wasn't suggesting using them in new designs (they're pretty much obsolete), but they're definitely better for high frequencies than most other common through-hole types (does anyone even make SMD carbon composition resistors?), like metal film and carbon film. --- Quote from: saturation on March 16, 2011, 12:48:37 am ---http://books.google.com/books?id=zpTnMsiUkmwC&pg=PA2&lpg=PA2&dq=carbon+composition+resistor+frequencies&source=bl&ots=B4EZgRvC7Y&sig=qJiDRN3VxUrlkxH2Rb2aQ5kBtLU&hl=en&ei=PASATfuTEsSM0QGujIX7Dw&sa=X&oi=book_result&ct=result&resnum=10&ved=0CFgQ6AEwCQ#v=onepage&q=carbon%20composition%20resistor%20frequencies&f=false --- End quote --- You can't view this page, viewing limit has been reached. What did it say? --- End quote --- |
| alm:
Thanks for the info, I wasn't aware of the parasitic capacitance. Most sources I've seen (eg. this and this, just random datasheets) seem to consider them superior to metal film for high frequency (thin film is obviously superior). The first datasheet recommends carbon composition for a part that has transition times of 20-30ns, not exactly GHz speed, but no 10MHz either. I find it suspicious that the graph has only one curve for carbon composition, I can't imagine parasitic capacitance having the same influence at say 1ohm and 1Mohm. I also doubt that all carbon composition resistors are useless beyond 10MHz, lots of equipment from the seventies and earlier was full of carbon composition (wirewound was inductive, and metal film expensive), many of it can go beyond 10MHz. I'd have to check if for example the Tek TM500 series (which uses lots of carbon composition and multiple plugins go up to 250MHz) use metal film in all places that need to pass high frequency. I believe carbon comp was frequently used as termination resistor, but if they'd only work up to <10MHz, they'd be almost useless, since you need fairly long cables to even notice the transmission line effect at that frequency. I just checked, the Tek PG-502 (250MHz pulse generator with a rise time of <1ns) uses two ~50ohm carbon composition resistors (as indicated in the electrical parts list) as switchable rear termination, with no reactive components nearby to compensate for parasitics. It would need about 350MHz bandwidth to reproduce the 1ns edge, can't imagine that the termination has a zero impedance (extrapolating from the graph you posted) at those frequencies. These were just the first resistors I checked, there are many more carbon composition resistors in there (and in similar equipment of that vintage). There are some 1% metal film resistors, but they're there because of accuracy/stability. This doesn't mean that carbon comp is superior to metal film for HF, but it does suggest that carbon comp works well beyond 10MHz. Maybe there are different ways of producing a carbon composition resistor? That would explain the conflicting data, although I've never seen something like a 'low-capacitance carbon comp resistor'. |
| grenert:
How about these MELF resistors? Vishay claims they're good to 10 GHz+ http://www.vishay.com/docs/28718/melfhf.pdf They say low inductance, but no mention of capacitance. |
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