EMRFD Message Archive 8841
Message Date From Subject 8841 2013-07-28 16:19:07 Bob L DC Phasing Rigs and SMT Devices We have been discussing the relative merits of a superhet versus DC phasing rigs.
I'd like to address the question of SMT devices in the DC rigs.
Much of the DC phasing literature has emphasized use of "poly" capacitors, apparently due to their tighter tolerances, reduced aging effects and reduced microphonics.
These components are expensive and not found the traditional junk box. Some of their values are unobtainium in low voltage packages. It seems overkill to build a 12 volt circuit using a big, 630 volt poly capacitor.
The recent NORCAL 2030 CW transceiver made me wonder about the benefits of SMT components in DC phasing rigs. Reading the manual there appears a dearth of "plastic" capacitors. But the advertised specs place it near the top of the heap.
Do SMT capacitors avoid some of the shortfalls of traditional through hole components?
When I google the web, looking for recent experimentation on SMT components in DC rigs, I don't see much. I wonder, why?
8842 2013-07-28 16:42:45 kb1gmx Re: DC Phasing Rigs and SMT Devices 8843 2013-07-28 17:38:52 Thomas S. Knutsen Re: DC Phasing Rigs and SMT Devices Like those in the "all-pass pcb" folder in the group files page?
> Whats needed is a laid out SMT all-pass board.--
Please avoid sending me Word or PowerPoint attachments.
PDF is an better alternative and there are always LaTeX!
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8844 2013-07-28 19:43:53 Andy Re: DC Phasing Rigs and SMT Devices > For the common (KK7B) all-pass networks the caps only have to beThe tempco of most ceramic caps is not so good. Are they pretty much
> the same (10nf) and there are plenty of SMT parts to fill that need.
> A few minutes with a AADE or other capacitor measuring system
> can match them up easily.
guaranteed to track one another vs. temp., aging, etc.?
How about ESR or DF; how important are they in those filters?
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8846 2013-07-28 20:43:30 William Carver Re: DC Phasing Rigs and SMT Devices ONLY NPO/C0G ceramic would be stable. 10,000 pF is pretty large value
for NPO but they do exist. Not cheap, not tight tolerance so matching a
group might require a slightly larger set. Although sometimes sequential
capacitors from a length of tape are close in value.
Film capacitors could be a better bet for matching. Panasonic makes .01
uF in 2% tolerance. They're SMD but larger that common SMD parts: 0.19"
x 0.13". They are over a dollar each, but less than $40 for fifty of
them, hi. That would be an adequate set size!
On Sun, 2013-07-28 at 22:43 -0400, Andy wrote:
> > For the common (KK7B) all-pass networks the caps only have to be
> > the same (10nf) and there are plenty of SMT parts to fill that need.
> > A few minutes with a AADE or other capacitor measuring system
> > can match them up easily.
> The tempco of most ceramic caps is not so good. Are they pretty much
> guaranteed to track one another vs. temp., aging, etc.?
> How about ESR or DF; how important are they in those filters?
> [Non-text portions of this message have been removed]
8848 2013-07-29 06:05:12 John Levreault Re: DC Phasing Rigs and SMT Devices As for SM caps for active filters, I've had good luck with Panasonic PPS
(polyphenylene sulfide) film caps. They're available from Digikey in 2%
tolerance and a 1206 package. According to the Panasonic data sheet, their temp
stability is within 1% up to 70°C and down to -40. Their capacitance,
dissipation factor, and insulation resistance are all very stable. IMO, a far
better choice for active filters (including phase-shift networks) than ceramics,
even NPO's. 0.01uf's are ~38c apiece in 100's.
One plug in favor of SM: You only work on one side of the board! No flipping it
over after insertion to do your soldering. And 1206-size packages are pretty
easy to handle.
8849 2013-07-29 07:34:58 Bob L Re: DC Phasing Rigs and SMT Devices SMT also eliminates drilling holes for through-hole devices.
I read that some poly SMT capacitors are easily damaged with hand soldering tools. They are designed to survive reflow soldering protocols. Is this true?
Are through hole caps more prone to microphonics than SMT's?
My AADE L/C meter was well worth the money.
8850 2013-07-29 08:20:03 John Levreault Re: DC Phasing Rigs and SMT Devices 8851 2013-07-29 09:03:29 kb1gmx Re: DC Phasing Rigs and SMT Devices Yes and no.
Yes smt for caps. No as it is the older miniR2 schematic and lacks the phase and amplitude adjustments. Also the 358 opamp while ok
is not the quietest.
The general idea is good though.
8852 2013-07-29 09:08:40 kb1gmx Re: DC Phasing Rigs and SMT Devices 8853 2013-07-30 04:05:57 Gian Re: DC Phasing Rigs and SMT Devices Hi Allison, Bill (W7AAZ) and all,
very interesting discussion.
What about using Murata Caps available from mouser
Codice prodotto del produttore:
These are 10nF 1% C0G 50V 1206 SMD at .189 (ca 0.250$) x 100
8854 2013-07-30 05:29:08 victor Re: DC Phasing Rigs and SMT Devices These Murata capacitors are excellent for the phasing network.
In my homebrew DC phasing transceiver I have used 33nF 5% NPO SMT capacitors, selected for value matching by hand and it works perfectly.
NPO capacitors are not microphonic (At least I don't feel it) so no problem using them.
Victor - 4Z4ME
8855 2013-07-30 06:03:29 William Carver Re: DC Phasing Rigs and SMT Devices Nice find, Gian. I didn't see those when I browse Mouser cataloge.
Didn't know anyone made 50V NPO that large in 0805 package. $0.37 in 10s
is a lot cheaper than I would expect, too.
On Tue, 2013-07-30 at 11:05 +0000, Gian wrote: