K3: IF output buffer gain modification
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I've just gone through the last 800 or so recent reflector messages (I
haven't downloaded my email in a few days), and not a single one was devoted to this hardware modification. I have a couple of questions: 1. What is this mod for? I'm assuming it's for the Elecraft panadaptor, but why do we need to mod the K3? Couldn't the IF output be amplified by the panadaptor? I'm not really comfortable cutting stuff out of my 4 thousand dollar investment. 2. If I do decide to buy the panadaptor, can Elecraft perform this modification for me if I send the radio back? I've already done most of the hardware mods, but SMD stuff I refuse to deal with. 73 de James K2QI ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
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> 1. What is this mod for? I'm assuming it's for the Elecraft panadaptor, > but why do we need to mod the K3? Couldn't the IF output be amplified by > the panadaptor? I'm not really comfortable cutting stuff out of my 4 > thousand dollar investment. > In some circumstance, the IF output level is weaker than the signal at the antenna connector, so the S/N suffers. This mod adds gain back in the appropriate location so the attached panadaptor will be able to display signals as weak as you can hear on the K3 itself. 73, Lyle KK7P ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
Re: K3: IF output buffer gain modification
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In reply to this post by K2QI
On Mon, 2009-09-21 at 22:15 -0400, James Sarte wrote:
> I've just gone through the last 800 or so recent reflector messages (I > haven't downloaded my email in a few days), and not a single one was devoted > to this hardware modification. I have a couple of questions: > > > > 1. What is this mod for? I'm assuming it's for the Elecraft panadaptor, > but why do we need to mod the K3? Couldn't the IF output be amplified by > the panadaptor? It's a noise figure issue. Amplifying the IF output can only do so much to improve the NF. (At some point you're just amplifying the noise.) That said, the P3 should work pretty well even without the IF out mod to the K3. Normal band noise is high enough that in most cases you should be able to see pretty much anything you can hear. > I'm not really comfortable cutting stuff out of my 4 > thousand dollar investment. It's an easy mod. Just remove one surface-mount resistor (cut it in half with side cutters and then clean the pads with a soldering iron) and solder in either a replacement SMT part or a leaded part using a handy nearby via hole in the PC board. Details are at: http://www.elecraft.com/K3/k3_app_notes.htm Alan N1AL ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
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Alan Bloom wrote:
>It's an easy mod. Just remove one surface-mount resistor (cut it in >half with side cutters That is a very risky technique - cutters apply a very large and uncontrolled force which can easily tear up the solder pads. It is much safer to melt the solder at both ends of the resistor, swapping quickly between one end and the other, until the resistor gently slides off. (Also a query about the resistor value: does it truly have to be 13K? Is this potential divider so critical that it cannot use one of the readily available standard values of 15K, 12K or even 10K?) -- 73 from Ian GM3SEK 'In Practice' columnist for RadCom (RSGB) http://www.ifwtech.co.uk/g3sek ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
Re: K3: IF output buffer gain modification
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In reply to this post by K2QI
I find removing surface mount resistors, at least on the underside of
the K3 main board, quite simple. It's easier than removing wire ended resistors from plated through holes! Remove the bulk of the solder from each end of the component with solder wick, the heat from the iron will often have migrated through the component by this time and it will slide away from the pads, if not dab the other end. I really do not like cutting surface mount resistors and capacitors with side cutters as a means of removing them. Getting the replacement component nice and square on the board is harder than removing the old one as the heat from soldering the second end can be enough to cause the component to shift slightly. 73 Dave, G4AON K3/100 #80 with all the published mods. ---------------------------- Ian GM3SEK wrote: >/It's an easy mod. Just remove one surface-mount resistor (cut it in />/half with side cutters / That is a very risky technique - cutters apply a very large and uncontrolled force which can easily tear up the solder pads. ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
Re: K3: IF output buffer gain modification
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In reply to this post by K2QI
I entirely understand your concern, but having plucked up the courage to do a couple of mods a few months ago I found it really wasn't difficult. Getting an SMT part off is a lot easier than removing through hole parts (believe me, I have the messy looking KSB2 with lifted circuit traces in my K2 to show for it.) I used two soldering irons, one at each end, and the resistor was off in a jiffy. I haven't looked at this particular mod yet since I don't have a need for it but I assume, as with the other mod, that the replacement resistor can be a leaded one if you find that easier.
Julian, G4ILO. K2 #392 K3 #222 KX3 #110
* G4ILO's Shack - http://www.g4ilo.com * KComm - http://www.g4ilo.com/kcomm.html * KTune - http://www.g4ilo.com/ktune.html |
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In reply to this post by gm3sek
When the mod was first published I asked: "Just checking to see if this is a typo. 13K or 12K?" Bob Friess N6CM (the 1st mixer designer) replied: "13K is a standard 5% value and is correct." I took the 5% tolerance to mean the value is somewhat critical. 73, Bill |
Re: K3: IF output buffer gain modification
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In reply to this post by K2QI
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Re: K3: IF output buffer gain modification
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In reply to this post by Bill W4ZV
On Tue, 2009-09-22 at 03:50 -0700, Bill W4ZV wrote:
> > When the mod was first published I asked: > "Just checking to see if this is a typo. 13K or 12K?" > > Bob Friess N6CM (the 1st mixer designer) replied: > "13K is a standard 5% value and is correct." 13k is not standard in the bag of SMT resistors I have here ;-) so in the 3 K3's I have carried this mod out in so far I used 1K and 12k in series. SMT allows this to be done relatively neatly by standing off each resistor at approximately 45 degrees from the pad, touching in the middle. then solder Takes a bit of fiddling around but it can be done -- 73 Brendan EI6IZ ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
Re: K3: IF output buffer gain modification
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In reply to this post by K2QI
There is about 0.2 dB difference between using one value or the other,
depending on the accuracy of your model. 73 Dave, G4AON K3/100 #80 ------------------ Bill W4ZV wrote: When the mod was first published I asked: "Just checking to see if this is a typo. 13K or 12K?" Bob Friess N6CM (the 1st mixer designer) replied: "13K is a standard 5% value and is correct." I took the 5% tolerance to mean the value is somewhat critical. ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
Re: K3: IF output buffer gain modification
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In reply to this post by gm3sek
13k is a standard value in the progression of 5% resistors (10, 11, 12,
13, 15, 18, 20, etc.). It is difficult to get 10% resistors anymore, and 5% tolerance is normally used. If your local parts source does not have them, perhaps they are only stocking those values from the list of 10% tolerance values to save shelf space. 73, Don W3FPR Ian White GM3SEK wrote: > (Also a query about the resistor value: does it truly have to be 13K? > Is this potential divider so critical that it cannot use one of the > readily available standard values of 15K, 12K or even 10K?) > > > ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
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In reply to this post by Dave, G4AON
Dave G4AON wrote:
> >Bill W4ZV wrote: > >>When the mod was first published I asked: >>"Just checking to see if this is a typo. 13K or 12K?" >> >>Bob Friess N6CM (the 1st mixer designer) replied: >>"13K is a standard 5% value and is correct." >> >>I took the 5% tolerance to mean the value is somewhat critical. >> >There is about 0.2 dB difference between using one value or the other, >depending on the accuracy of your model. > 13K is a standard value in the E24 series, which covers a full decade in 24 steps. Each step is about 10% above the previous value, so E24 resistors have to be manufactured with a tolerance of 5% or better. http://www.logwell.com/tech/components/resistor_values.html But *standard* values aren't the same as the most-used *common* values. The ones most used are the well known E6 series (1.0, 1.5, 2.2 etc) or the E12 series (1.0, 1.2, 1.5, 1.8, 2.2 etc). Most RF circuits don't operate within 5% margins, so they can get along fine with E6 and E12 values. -- 73 from Ian GM3SEK http://www.ifwtech.co.uk/g3sek ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
Re: K3: IF output buffer gain modification
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In reply to this post by gm3sek
On Tue, 2009-09-22 at 08:22 +0100, Ian White GM3SEK wrote:
> (Also a query about the resistor value: does it truly have to be 13K? > Is this potential divider so critical that it cannot use one of the > readily available standard values of 15K, 12K or even 10K?) No, the exact value is not critical. Alan N1AL ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
Re: K3: IF output buffer gain modification
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In reply to this post by Alan Bloom-2
On Tue, 2009-09-22 at 19:08 -0400, amstel78 wrote:
> So would it be advisable to wait for the P3 to come out before > performing this modification? If it's not really needed, then what's > the point? My antenna system isn't that great anyway... I need to do some more experimenting to get a better handle on this, but I think it just depends on conditions. With the K3 preamp off on a quiet band (e.g. VHF) you definitely want the mod. On 80 meters in the summertime it's not necessary. If you don't do the mod you might need to use the preamp more often than you otherwise would. There's no reason not to do the modification other than the hassle factor. The P3 automatically bypasses its own preamplifier if the signal starts to over-range. Alan N1AL ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
Re: K3: IF output buffer gain modification
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Are there any thoughts as to the accuracy level in dBm in correlation
with this mod? As well as any sort of absolute accuracy specs on what we expect to see with this box? On Tue, 2009-09-22 at 16:58 -0700, Alan Bloom wrote: > On Tue, 2009-09-22 at 19:08 -0400, amstel78 wrote: > > > So would it be advisable to wait for the P3 to come out before > > performing this modification? If it's not really needed, then what's > > the point? My antenna system isn't that great anyway... > > I need to do some more experimenting to get a better handle on this, but > I think it just depends on conditions. With the K3 preamp off on a > quiet band (e.g. VHF) you definitely want the mod. On 80 meters in the > summertime it's not necessary. If you don't do the mod you might need > to use the preamp more often than you otherwise would. > > There's no reason not to do the modification other than the hassle > factor. The P3 automatically bypasses its own preamplifier if the > signal starts to over-range. > > Alan N1AL > > > ______________________________________________________________ > Elecraft mailing list > Home: http://mailman.qth.net/mailman/listinfo/elecraft > Help: http://mailman.qth.net/mmfaq.htm > Post: mailto:[hidden email] > > This list hosted by: http://www.qsl.net > Please help support this email list: http://www.qsl.net/donate.html ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
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> Are there any thoughts as to the accuracy level in dBm in correlation
> with this mod? As well as any sort of absolute accuracy specs on what > we expect to see with this box? The absolute accuracy will almost certainly not be better than about +/- 2.0 dB... which is the best that spectrum analyzers from Rohde&Schwarz, Agilent, and others could do. Most people are quite surprised to hear that their US$70,000 spectrum analyzer could be off by 2.0 dB. But that is the reality. An error analysis of a spectrum analysis measurement is well-known: frequency response, mismatch, IF gain (reference level), and calibrator uncertainty all come into play. The result is somewhere in the neighborhood of +/- 1.8 dB or worse. That is considered quite good! When making a relative measurement (the difference between two signals) it's even worse. For more information and specific examples, see http://cp.literature.agilent.com/litweb/pdf/5968-3659E.pdf . The main thing to remember is that a panadaptor display is good, but it's not absolutely accurate in power. If you need excellent power accuracy, you must use a power meter. There are a lot of stages before the P3 panadaptor that conspire to increase the measurement uncertainty. Consider that before the signal even reaches the receiver it has already undergone the loss in the transmission line and the connectors. Do you know exactly how much loss you have in your transmission line and connectors? Following this, the signal then hits the receiver input which is not exactly 50 ohms. It could be 20. Or 90. Because it's not exactly 50, there is mismatch uncertainty. Already two errors right there. On the inside of the rx, there are a number of switches, cables, and bandpass filters (with amplitude ripple), then an attenuator and RF amp, mixer, and post-mixer amp. Take the attenuator for example. It might claim that its loss is -10 dB, but that's a nominal value that will actually be different for every K3. Each of the stages mentioned has an uncertainty in its gain, loss, or match which must be added to the total uncertainty. So these are all of the errors that add up to the figure I quoted at the outset. You might have better accuracy that this, but the point is you won't know if you do, so you must assume the worst case. Al W6LX ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
Re: K3: IF output buffer gain modification
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If it were within +/- 2.0dB absolute accuracy I'd be tickled pink.
However your comments about spectrum analyzers today are a bit dated. Power meters are becoming much less crucial for getting accurate readings. We just bought a new spectrum analyzer from Agilent which with all the options we got only cost around 55,000. This unit is an N9020A and its very accurate. Their specification is +/- .23 dB absolute accuracy and it matches with our power meter dead nuts on. The thing even has a 35dB preamp with 10dB NF built in and it covers almost the full bandwith of the unit (100Khz to 13.6Ghz). The unit itself can measure down to 3Hz. Its not that I needed to understand what went into the calculation and while the question may have sounded ignorant I was more looking for a value than an explanation why it was worse than some may have thought I was looking for. ~BTH On Tue, 2009-09-22 at 20:40 -0700, Al Lorona wrote: > > Are there any thoughts as to the accuracy level in dBm in correlation > > with this mod? As well as any sort of absolute accuracy specs on what > > we expect to see with this box? > > The absolute accuracy will almost certainly not be better than about +/- 2.0 dB... which is the best that spectrum analyzers from Rohde&Schwarz, Agilent, and others could do. > > Most people are quite surprised to hear that their US$70,000 spectrum analyzer could be off by 2.0 dB. But that is the reality. An error analysis of a spectrum analysis measurement is well-known: frequency response, mismatch, IF gain (reference level), and calibrator uncertainty all come into play. The result is somewhere in the neighborhood of +/- 1.8 dB or worse. That is considered quite good! When making a relative measurement (the difference between two signals) it's even worse. For more information and specific examples, see http://cp.literature.agilent.com/litweb/pdf/5968-3659E.pdf . > > The main thing to remember is that a panadaptor display is good, but it's not absolutely accurate in power. If you need excellent power accuracy, you must use a power meter. > > There are a lot of stages before the P3 panadaptor that conspire to increase the measurement uncertainty. Consider that before the signal even reaches the receiver it has already undergone the loss in the transmission line and the connectors. Do you know exactly how much loss you have in your transmission line and connectors? Following this, the signal then hits the receiver input which is not exactly 50 ohms. It could be 20. Or 90. Because it's not exactly 50, there is mismatch uncertainty. Already two errors right there. > > On the inside of the rx, there are a number of switches, cables, and bandpass filters (with amplitude ripple), then an attenuator and RF amp, mixer, and post-mixer amp. Take the attenuator for example. It might claim that its loss is -10 dB, but that's a nominal value that will actually be different for every K3. Each of the stages mentioned has an uncertainty in its gain, loss, or match which must be added to the total uncertainty. > > So these are all of the errors that add up to the figure I quoted at the outset. You might have better accuracy that this, but the point is you won't know if you do, so you must assume the worst case. > > Al W6LX > > ______________________________________________________________ > Elecraft mailing list > Home: http://mailman.qth.net/mailman/listinfo/elecraft > Help: http://mailman.qth.net/mmfaq.htm > Post: mailto:[hidden email] > > This list hosted by: http://www.qsl.net > Please help support this email list: http://www.qsl.net/donate.html ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
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> We just bought a new spectrum analyzer from Agilent which
> with all the options we got only cost around 55,000. This unit > is an N9020A and its very accurate. Yes, that's a beautiful instrument, Brett. I guess my comments were directed toward the 1000's of older conventional analyzers out there. However, it is still instructive to temper your (Agilent's) claims for absolute accuracy a little bit. Allow me to be a real stickler for a moment: The +/- 0.23 dB spec is what Agilent calls the "95th percentile" spec, meaning that 95% of the units will probably meet it. But it is not guaranteed. Furthermore, the data sheet for that signal analyzer says that the guaranteed spec is: +/- 0.33 dB + 0.6 dB frequency response error below 10 MHz = approx. +/- 1 dB. So this is closer to the spec that I would quote someone. Note that I'm not adding in the uncertainty due to mismatch (which appears to be 1.2:1 at the instrument's input in the HF range). Note that that analyzer also calibrates itself *after every sweep* with an internal power meter! Yours may be really close to your power meter's reading, but if you didn't have that power meter to tell you that, your uncertainty would have been the figure I gave above. I loved your "only $55,000" comment. :^) Regards, Al W6LX ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[hidden email] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html |
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