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Hi all
I want to clear up any confusion about the types of capacitors and toroids used in the QRP Labs kits. The following applies to all QRP Labs kits, not just the QCX.
About capacitors:
All QRP Labs kits use low loss multi-layer ceramic NP0 capacitors for all capacitance values below 5nF. This includes all the LPF and BPF kit capacitors for HF bands. These capacitors are also sometimes known as C0G, CC4 or Class-I dielectric types. The voltage rating of these capacitors is adequate for up to 10W.
The very first QRP Labs kit, introduced at Dayton FDIM 2010, was a simple ATtiny13-controlled FSKCW transmitter. If you are interested you can see details of it here: . Hundreds of people happily built these and operated them. However a small handful of customers possessing VNA or Spectrum analyser/tracking generator equipment spent some time examining every detail of the kit, as they enjoyed doing. These LPFs were lossy and it was because I had used the cheapest common type of ceramic capacitor. One OM called them "molded mud"! I have learned from my mistake, and all the kits since then have used the more expensive NP0 type. Well, when you buy 1000 each time, they anyway become not so much more expensive? ;-)
About inductors:?
QRP Labs uses toroids from several suppliers, sometimes micrometals, sometimes equivalents, practically-speaking according to availability. Batches from every supplier have been tested by me, and verified to have equivalent characteristics to the specified micrometals ones (within tolerance). I'm fact sometimes the alternative manufacturer toroids outperform micrometals on their Q. This has also been verified by other constructors.?
People should also note that there is a range of inductance of a toroid with n turns, depending how tightly the turns are wound and how spread they are around the core. This range is quite wide! The theoretical calculation of inductance for a given number of turns (which is also found in many online toroid calculator tools), assumes an even distribution of turns around the core. In practice everyone always leaves a gap - in fact they SHOULD do so, because otherwise there may be capacitance between the two ends of the inductance, which will alter the filter performance also. But I have found that many people tend to leave a larger gap than is necessary or desirable. Squeezing the turns of a toroid increases the inductance. Therefore leaving a larger gap increases the inductance. Actually ANY kind of non-even winding will cause the inductance to be higher than expected!
This quote is from the Micrometals app note entitled "Iron Powder Cores for High Q Inductors" states:
"Another characteristic, which affects the apparent inductance, is leakage inductance. Leakage inductance acts in series with the coil's self-inductance.? This is a result of un-coupled flux and becomes most apparent in high frequency, low inductance coils particularly when the turns are not evenly distributed around the core. Here is an example where a T50-17 is wound with 10 turns #20 (μ = 4). In cases like this where it is possible to drastically change the positioning of the turns, and the permeability of the core material is low, very large differences are seen. In higher permeability materials this affect is much less. In a number of applications, toroidal coils are tuned by this means."
Where the number of turns of wire is smaller, the range of adjustment is therefore larger. In any event, everything always seems to get worse when you go up to higher frequencies. I believe this is why we more often hear of "low power" problems on 20m, than say, 40m.?
Some people feel that measuring the inductance value with an LC-meter prior to installation is helpful. In general I would agree with this. But even then, caution is required because in many cases the accuracy of these LC meters is unknown or suspect; and some people say that the measurement of inductance at much lower frequencies than will be used in the application, also gives a differing result (I am not sure how true this is).?
Heating of components can occur when the Low Pass Filter has attenuation at the operating frequency. It is a simplification to say that if the PA produces 5W of power, and if only 3W come out the other end of the LPF, then 2W has been lost in the filter - and this 2W must go into heating the components! Nevertheless, the simplification does have some validity. And since the capacitors are small, if they dissipate power their temperature can rise quickly (or in other words, not much power dissipation is required to raise the temperature significantly).?
The output power of the QCX is dependent on supply voltage. This simple fact is often missed by constructors. Getting 2.5 or 3W at 12V supply is normal. To get 5W output does require 15 or 16V. This is what I have found on all my QCX here too. The power output of the three BS170s is a little less than the maximum that would be possible; this is because a little voltage is dropped across the 1N5819 Schottky diode which is used for reverse polarity protection of the radio at its power supply connector; and a little more voltage is lost in the key-shaping transistor. These two features (reverse polarity protection and CW envelope shaping) are very important, so worth the little reduction in power.?
It is also the case that many constructors do not appreciate the difference that 1W of power makes (for example, whether they use 4W or 5W) is rather smaller than it looks, if you consider it in dBm terms, which is what is actually important. Or equivalently, a quite small fraction of an S-point.?
Finally, the measurement of power itself is difficult to make accurately. To get an accurate power measurement requires transmitting into a known good 50-ohm dummy load. Many power meters have accuracy limitations. Usually a small difference in peak or RMS voltage measurement, leads to a bigger difference in calculated power (since the voltage is squared in the formula). So any inaccuracies are multiplied.?
There are people who build their QCX and plug it in and measure 5W at 12V supply and are very happy about that. Personally I find that much power, at 12V supply, rather unlikely. Then there are other people who measure less.?
The simplest way to deal with it, for people who think that they have less power than they expect, but lack the means to make detailed measurements, is to just remove a turn or two from the inductors L1, L2, L3.?
All of the above is a theoretical explanation, and a description of the quality of components that are used in the QRP Labs kits. However, none of this removes the possibility that a particular component might be drastically out of tolerance; or defective, or the possibility of supplier error, etc. In these cases I would need to undertake a further investigation if there was a widespread problem. But I do not think there is any widespread problem, from all I have heard to date.?
73 Hans G0UPL
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Very helpful summary Hans.
Thanks for the detail,
Rich N1IXF
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Update: the 180 pF capacitors are fine, it's only the 390 pF ones that drift over temperature and have poor Q.
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Hi I had troubled with the 390 PF caps 20MLPF, they were turquoise in colour. I am sure Hans in on the case. ? 73 ? Andrew ? ? ?
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From: [email protected] [mailto:[email protected]] On Behalf Of andrey@...
Sent: 13 March 2018 19:26
To: [email protected]
Subject: Re: [QRPLabs] A word about QRP Labs capacitors and toroids ? Update: the 180 pF capacitors are fine, it's only the 390 pF ones that drift over temperature and have poor Q.
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Please find enclosed before and after I discovered this September 17, but now one seem that bothered. ? 73 ? Andrew ?
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From: [email protected] [mailto:[email protected]] On Behalf Of andrey@...
Sent: 13 March 2018 18:53
To: [email protected]
Subject: Re: [QRPLabs] A word about QRP Labs capacitors and toroids ? Thank you for the informative post Hans.
It does appear that at least the capacitors shipped with my 20m LPF kit were not NP0. I did some measurements on the capacitors after discovering that my LPF kit had more than 2 dB insertion loss at the target frequency.
Test #1: I measured capacitance with an accurate LCR meter over a temperature range by using a can of compressed air turned upside down. The kit capacitor changed from 375 pF to 335 pF -- a change of over 10%. By contrast, the replacement NP0 capacitor I got from Digikey stayed at exactly 389 pF during this test (not even 1 pF of change).
Test #2: I built an LC tank circuit using a toroidal inductor and measured its frequency response with both the kit and the replacement capacitors:
The kit capacitor is the curve that doesn't resonate as strongly, suggesting that the capacitor has losses at RF frequency (10 MHz in this example).
The 180 pF and 390 pF capacitors I got in my kit look like this:
Perhaps there was a mixup in the supply chain? I ordered my kits a few months ago, around August 2017 if I remember correctly.
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Andy,
I am just in the process of assembling my QCX 20m kit. It arrived yesterday, serial 3647. My 390pF LPF capacitors look identical to yours but show no capacitance change when threatened with a soldering iron applied to a lead.
When I used a kit 390pF to make a parallel tuned circuit with a T50-6 toroid and put it in series between my tracking generator and spectrum analyser input I see a notch depth of 21dB. If I replace the kit capacitor with a 390pF silvered mica I get a notch depth of 28dB, which is what I'd expect if my 330nH coil has a Qu=200. Although I think my kit caps are not as bad as yours I guess they are still not very good: a circuit simulator suggests if the coil has 0.145 ohms ESR then for a 21dB notch the kit capacitor has an ESR of 0.65 ohms and a Qu=45.
I'll wind another coil and check the 180pF LPF caps tomorrow.
73, Alan G3XAQ
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On Tue, Mar 13, 2018 at 12:25 pm, @Andy24 wrote:
Update: the 180 pF capacitors are fine, it's only the 390 pF ones that drift
over temperature and have poor Q.
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Andrew - those charts are almost identical to my measurements. I had around 2 dB of insertion loss with the old 390 pF caps, 0.25 dB with NP0 replacements. Alan - a regular 390pF NP0 ceramic capacitor produced a 31 dB notch in my tank circuit, no need for silver mica. I used this capacitor from Digikey:
Andrey, KD1T
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Hello Andrew, Alan, Andrey
Thank you for the information. I am investigating the 390pF capacitors.?
73 Hans G0UPL
On Wed, Mar 14, 2018 at 4:05 AM, <andrey@...> wrote: Andrew - those charts are almost identical to my measurements. I had around 2 dB of insertion loss with the old 390 pF caps, 0.25 dB with NP0 replacements.
Alan - a regular 390pF NP0 ceramic capacitor produced a 31 dB notch in my tank circuit, no need for silver mica. I used this capacitor from Digikey:
Andrey, KD1T
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So it seems there is a quality problem with the 560pF turquoise-coloured caps as well as their 390pF cousins.
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On Wed, Mar 14, 2018 at 04:18 am, Adrian Scripc? wrote:
Hey Andrew, Alan, Andrey,
Just wanted to +1 the issue. After removing some turns from L1, L2, L3 on
my 30m QCX I managed to increase the output power by moving the filter
cutoff upward but the insertion loss was still high compared to others',
somewhere around ~1.5dB. I just replaced C25 and C26 with some polystyrene
capacitors (I didn't have NPOs for these values) and the output power went
up nicely, in accordance with the specified numbers. I get ~3.1W at 11.8V
(after the diode). The filter IL also went down to 0.64dB as you can see
from the attached pictures; it's still larger than others have mentioned
but I'm happy with the result.
I also attached a pic with the kit capacitor (turquoise) and the type that
I replaced them with. I purchased those capacitors from Diz, long ago.
73 and all the best,
Adrian, YO6SSW
On Wed, Mar 14, 2018 at 12:03 PM, Hans Summers <hans.summers@...>
wrote:
Hello Andrew, Alan, Andrey
Thank you for the information. I am investigating the 390pF capacitors.
73 Hans G0UPL
On Wed, Mar 14, 2018 at 4:05 AM, <andrey@...> wrote:
Andrew - those charts are almost identical to my measurements. I had
around 2 dB of insertion loss with the old 390 pF caps, 0.25 dB with NP0
replacements.
Alan - a regular 390pF NP0 ceramic capacitor produced a 31 dB notch in my
tank circuit, no need for silver mica. I used this capacitor from Digikey:
ts/K391J15C0GF5TL2/BC1020CT-ND/286642
Andrey, KD1T
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Hans, ? I’m still in the throes of assembling my 20m kit……1/2 hour at a time…. And read these potential problems with the caps in the LPF. IF you do find there is a problem with these caps do you intend to notify us so we can buy caps that doesn’t have the problems? Hans, I’m really getting to old to have any more problems!? J ? Al? ?
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From: [email protected] [mailto:[email protected]] On Behalf Of Hans Summers
Sent: Wednesday, March 14, 2018 6:03 AM
To: [email protected]
Subject: Re: [QRPLabs] A word about QRP Labs capacitors and toroids ? Hello Andrew, Alan, Andrey Thank you for the information. I am investigating the 390pF capacitors.? ? On Wed, Mar 14, 2018 at 4:05 AM, <andrey@...> wrote: Andrew - those charts are almost identical to my measurements. I had around 2 dB of insertion loss with the old 390 pF caps, 0.25 dB with NP0 replacements.
Alan - a regular 390pF NP0 ceramic capacitor produced a 31 dB notch in my tank circuit, no need for silver mica. I used this capacitor from Digikey:
?
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I have a 40, 20 and 15m(17m modded) QCX and plan to insert 1206 SMD NPO for all the LPF caps. Easy to do really, I actually find when experimenting the 1206 SMD are easier and quicker to work with than TH components!
73, NIck VK4PLN
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Hi Al
Sure, I will inform you the outcome. It will take a couple of weeks because I have to get samples of everything and it takes time in the post etc., then test etc.?
Meanwhile, don't worry too much. Over 4,000 QCX kits have been sold and about 30% of those are on 20m. The vast majority have been constructed without any problems.?
73 Hans G0UPL
On Wed, Mar 14, 2018 at 8:08 PM, Allen Poland <atpoland@...> wrote: Hans, ? I’m still in the throes of assembling my 20m kit……1/2 hour at a time…. And read these potential problems with the caps in the LPF. IF you do find there is a problem with these caps do you intend to notify us so we can buy caps that doesn’t have the problems? Hans, I’m really getting to old to have any more problems!? J ? Al? ? From: [email protected] [mailto:[email protected]] On Behalf Of Hans Summers
Sent: Wednesday, March 14, 2018 6:03 AM
To: [email protected]
Subject: Re: [QRPLabs] A word about QRP Labs capacitors and toroids ? Hello Andrew, Alan, Andrey Thank you for the information. I am investigating the 390pF capacitors.? ? On Wed, Mar 14, 2018 at 4:05 AM, <andrey@...> wrote: Andrew - those charts are almost identical to my measurements. I had around 2 dB of insertion loss with the old 390 pF caps, 0.25 dB with NP0 replacements.
Alan - a regular 390pF NP0 ceramic capacitor produced a 31 dB notch in my tank circuit, no need for silver mica. I used this capacitor from Digikey:
?
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Thank you Hans.? This makes me feel much better.? I figure this kit is my last “hoorah” in building and I’m as nervous as a dog shittin razor blades! ? BTW, who makes the headers and pin connectors used for the display? I sure would love to get my hands on a crimp tool because I want to remote the display. ? Al ?
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From: [email protected] [mailto:[email protected]] On Behalf Of Hans Summers
Sent: Thursday, March 15, 2018 2:50 AM
To: [email protected]
Subject: Re: [QRPLabs] A word about QRP Labs capacitors and toroids ? Hi Al Sure, I will inform you the outcome. It will take a couple of weeks because I have to get samples of everything and it takes time in the post etc., then test etc.? Meanwhile, don't worry too much. Over 4,000 QCX kits have been sold and about 30% of those are on 20m. The vast majority have been constructed without any problems.? ? On Wed, Mar 14, 2018 at 8:08 PM, Allen Poland <atpoland@...> wrote: Hans, ? I’m still in the throes of assembling my 20m kit……1/2 hour at a time…. And read these potential problems with the caps in the LPF. IF you do find there is a problem with these caps do you intend to notify us so we can buy caps that doesn’t have the problems? Hans, I’m really getting to old to have any more problems!? J ? Al? ? From: [email protected] [mailto:[email protected]] On Behalf Of Hans Summers
Sent: Wednesday, March 14, 2018 6:03 AM
To: [email protected]
Subject: Re: [QRPLabs] A word about QRP Labs capacitors and toroids ? Hello Andrew, Alan, Andrey Thank you for the information. I am investigating the 390pF capacitors.? ? On Wed, Mar 14, 2018 at 4:05 AM, <andrey@...> wrote: Andrew - those charts are almost identical to my measurements. I had around 2 dB of insertion loss with the old 390 pF caps, 0.25 dB with NP0 replacements.
Alan - a regular 390pF NP0 ceramic capacitor produced a 31 dB notch in my tank circuit, no need for silver mica. I used this capacitor from Digikey:
?
?
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You are welcome, I have plots for most your Filters, all are text book! As I build more I will send them in. ? 17M looks the best ? BR ? Andrew ?
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From: [email protected] [mailto:[email protected]] On Behalf Of Hans Summers
Sent: 14 March 2018 10:03
To: [email protected]
Subject: Re: [QRPLabs] A word about QRP Labs capacitors and toroids ? Hello Andrew, Alan, Andrey Thank you for the information. I am investigating the 390pF capacitors.? ? On Wed, Mar 14, 2018 at 4:05 AM, <andrey@...> wrote: Andrew - those charts are almost identical to my measurements. I had around 2 dB of insertion loss with the old 390 pF caps, 0.25 dB with NP0 replacements.
Alan - a regular 390pF NP0 ceramic capacitor produced a 31 dB notch in my tank circuit, no need for silver mica. I used this capacitor from Digikey: ?
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Hello Andrew,
Could you do one for the 2200m filter please??
Friday, March 16, 2018
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You are welcome, I have plots for most your Filters, all are text
book! As I build more I will send them in. 17M looks the best BR Andrew -- 2E0ILY Best regards, Chris mailto:chris@...
--
Best regards, Chris Wilson (2E0ILY)
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Yes But need o order a few first ? 73 Andrew ? Sent from my Windows 10 phone ?
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From: Chris WilsonSent: 16 March 2018 12:30 To: [email protected]Subject: Re: [QRPLabs] A word about QRP Labs capacitors and toroids ? Hello Andrew, ? Could you do one for the 2200m filter please?? ? Friday, March 16, 2018 ? > You are welcome, I have plots for most your Filters, all are text > book! As I build more I will send them in. ? > 17M looks the best ? > BR ? > Andrew ? ? ? ? ? ? -- ? 2E0ILY Best regards, Chris??????????????????????????? mailto:chris@... ? ? ? -- Best regards, Chris Wilson (2E0ILY) ? ? ?
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Just relocked at this I consider 2200 M almost AF!!! However my VNA does go now to 10 KHZ ? BR Andrew ? Sent from my Windows 10 phone ?
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From: Chris WilsonSent: 16 March 2018 12:30 To: [email protected]Subject: Re: [QRPLabs] A word about QRP Labs capacitors and toroids ? Hello Andrew, ? Could you do one for the 2200m filter please?? ? Friday, March 16, 2018 ? > You are welcome, I have plots for most your Filters, all are text > book! As I build more I will send them in. ? > 17M looks the best ? > BR ? > Andrew ? ? ? ? ? ? -- ? 2E0ILY Best regards, Chris??????????????????????????? mailto:chris@... ? ? ? -- Best regards, Chris Wilson (2E0ILY) ? ? ?
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Hello Andrew,
137 kHz is damn near VHF these days ;)
2018-01-05 W4DEX to DL0A0 on 8269.9 Hz Distance 7257.9 Kms
A new world record distance for message decoding in the 36km band.
A recent successful transmission below 9kHz went from East to West
trans Atlantic, too.
On Friday, March 16, 2018 you said,
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Just relocked at this I consider 2200 M almost AF!!! However my VNA does go now to 10 KHZ BR Andrew -- 2E0ILY Best regards, Chris mailto:chris@...
--
Best regards, Chris Wilson (2E0ILY)
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On Wed, Mar 14, 2018 at 04:18 am, Adrian Scripc? wrote:
I just replaced C25 and C26 with some polystyrene capacitors (I didn't have NPOs for these values) and the output power went up nicely, in accordance with the specified numbers.
I?think Adrian may be on to something.??I had already removed windings on L1, L2 & L3 to get maximum power out on my 30m QCX, but after replacing C25 & C26 with polystyrene caps (same value), my power went from 2W to 3W on 12v, for a nice 50% increase.
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It appears that the stock caps are a bottleneck on 30m, and likely the other higher bands.?
?
Steve, N4IAG
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Andrew Lenton
Nick VK4PP