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Philips sold off its capacitor business to Vishay. Vishay also bought
the former Sprague capacitor line. Their capacitors should be a good
substitute.
I expect that capacitors from other quality manufacturers would also
work well. AVX, Kemet, Murata, and TDK are manufacturers that I know
of that make good ceramic capacitors. There are likely others as well.
All of those are available from the usual distributors.
If you want to focus on experimenting with filter design rather than
on capacitor testing, I recommend sticking with first-quality caps
from reputable sources. Leave the cheap caps from unknown sources in
China for less critical circuits, or for when you're in the next phase
of optimizing cost of a design.
toggle quoted message
Show quoted text
On Fri, Aug 17, 2018 at 3:33 PM, Arv Evans <arvid.evans@...> wrote: John VA7JBE
I might suggest using LTSpice to play with adding parallel caps and with
adding series traps.
This lets you juggle component values to match particular needs, and to see
the probable
attenuation these changes might provide.
Arv K7HKL
_._
On Fri, Aug 17, 2018 at 12:58 PM John VA7JBE via Groups.Io
<va7jbe@...> wrote:
I have a QCX20 in the mail and I'm wondering if it might be worth
replacing the LPF with one of the 'new' (1999) CWAZ filters presented by Ed
W3NQN in QEX,
. Based
on the simulations in the article, adding a capacitor in parallel with the
middle inductor to create a tuned circuit increases attenuation at the 2nd
harmonic and also reduces return loss in the 20m band (Figures 2 and 3.)
Has anybody tried playing with these filter designs before? Also, which
capacitors should I use? The article recommends the Philips 680 line of
ceramic capacitors but I've been having a hard time finding them. Would any
100V, NP0/C0G ceramic capacitor of reasonable tolerance do?
Cheers,
John VA7JBE
|
John? VA7JBE
I might suggest using LTSpice to play with adding parallel caps and with adding series traps.?
This lets you juggle component values to match particular needs, and to see the probable
attenuation these changes might provide.
Arv? K7HKL
_._
On Fri, Aug 17, 2018 at 12:58 PM John VA7JBE via Groups.Io <va7jbe= [email protected]> wrote: I have a QCX20 in the mail and I'm wondering if it might be worth replacing the LPF with one of the 'new' (1999) CWAZ filters presented by Ed W3NQN in QEX, .? Based on the simulations in the article, adding a capacitor in parallel with the middle inductor to create a tuned circuit increases attenuation at the 2nd harmonic and also reduces return loss in the 20m band (Figures 2 and 3.)? Has anybody tried playing with these filter designs before?? Also, which capacitors should I use?? The article recommends the Philips 680 line of ceramic capacitors but I've been having a hard time finding them.? Would any 100V, NP0/C0G ceramic capacitor of reasonable tolerance do?
Cheers,
John VA7JBE
|
I have a QCX20 in the mail and I'm wondering if it might be worth replacing the LPF with one of the 'new' (1999) CWAZ filters presented by Ed W3NQN in QEX, .? Based on the simulations in the article, adding a capacitor in parallel with the middle inductor to create a tuned circuit increases attenuation at the 2nd harmonic and also reduces return loss in the 20m band (Figures 2 and 3.)? Has anybody tried playing with these filter designs before?? Also, which capacitors should I use?? The article recommends the Philips 680 line of ceramic capacitors but I've been having a hard time finding them.? Would any 100V, NP0/C0G ceramic capacitor of reasonable tolerance do?
Cheers,
John VA7JBE
|
What I do, if for somehow, my 2~3 watts QRP doesn't make it to a rare DX station, I use it drive my HF Packer V4 (kit built) linear amplifier.? Using this amp, with about 2~3 watts of drive from my QCX 20m, I get about 30 watts to my antenna!? Thus, I don't feel like tearing in my operating QCX to get one more watt or so out of it and possibly destroying the PA transistors!? This above mentioned amp, operates 10 ~ 160m, SSB/CW; power out depends on band and mode.? I use this amp also with my Yaesu FT-817ND radio.? 73, de Karl, KO8S
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My experience with a 30m QCX? was exactly the same as Steve MW0KST. My unit as built had 2.5dB loss in the LPF and also too low a cutoff frequency when measured on a spectrum analyser, meaning that the filter roll-off was already a significant factor at 10.1-10.15MHz.
I replaced the two "blue blob" ceramic capacitors in the inner part of the PF and also took 1 turn off each of the three toroid coils in the LPF. Power output increased from less than 1W to around 2.5W with a 12V DC supply, which I'm happy with. Measuring the modified LPF on the spectrum analyser (and doing some modelling using RFSim99) convinced me that taking more than 1 turn off the coils would not give any further beneficial effect in my case.
These turquoise-blue blob capacitors do seem to be entirely unsuitable for use in the LPF as they appear to be low-Q/lossy - if you have these in the kit, my advice would be DO NOT use them - or if they've already been fitted, immediately replace them with higher-quality types (ceramics, polystyrene, SM or whatever - I used 160V polystyrene as that's what I had available).
73, Kevin ZL3KE
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I had 1.86W at 12.0 volts. Removed 1 turn each from coils L1, L2, L3. Increase output to 2.12 W, not a great change.?Measured loss prior to change was -2.29 dB through the filter at 14.020 MHz.
May replace capacitors next. Don't really mind 2 W since its QRP and 5 is too much, but can't let well enough alone.
Fred
WD9HNU
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Interesting what you did Choke to achieve more power from your QCX 20 xcvr.? I just measured mine yesterday, #748, that I built I built to the exact specifications in the manual.? My power output into a dummy load is:? 2.5 watts at 13.8volts and 3 watts at 15.0 volts.? There has been much discussion to power output levels with the QCX on 20m.? Yesterday, I upgraded the chip to version 1.00e, and did a modification to the QCX case to allow me to use the on board CW key.? 73, Karl, KO8S ?
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Interesting experiment. I had a miserable half a watt out of my 20m unit after completion at 13.8V DC which was a bit disappointing. In fact I was a bit deflated and put it away for the night. The next morning after some coffee, I stuffed the input signal of the filter on the scope and it looked about right for the expected 3.5-4W out so suspected the filter design. I yanked all the parts off and substituted the values in from the GQRP documentation on LPF design here:??... I naively assumed 50 ohms output from the PA which isn't necessarily the case but it worked. Got 4W out at 13.8V DC which is good and no heating problems with the PA throwing out WSPR into a dummy load as a test case.
I have since converted it to 30m which is a little quieter and easier to navigate as it is contest free. Unfortunately I appear to have knackered something during conversion as the audio gives out on the receiver and haven't had the time to fix it yet. Oops. Moral of the story: band conversion is risky; just buy another QCX :)
Chris
M0XTE
On Mon, 6 Aug 2018, at 15:51, chokelive E29AHU wrote:
Hi All,
I would like to share my experiment.
After a several month i have fixed output power for my QCX 20M? (my kit No.#487)
and now i can getting with full power 5 Watts @12Vdc
before I solve my QCX 20M. I can get output only 1.5 ~ 2w maximum
First i observe LPF circuit C25 and C26 (390pf) getting very hot during transmission.
This is my modification.
1. remove 1 turn of L1 and L3 (use only 15 turns) --> power improve abit to ~ 2.5w
2. remove C25 and C26 (390pf) and i replace with 2 series of MLCC capacitor 680pf (because there are in my stock) --> this big improve my power to 5w !!!
I believe?my issue is mismatch at LPF especially?at C25 and C26 (390pf).
thanks group for good knowledge?sharing?and Hans for the grate kits.?
73
Choke E29AHU
during experiment
finally soldering in the right place
output power @12vdc
|
Hi All,
I would like to share my experiment.
After a several month i have fixed output power for my QCX 20M? (my kit No.#487)
and now i can getting with full power 5 Watts @12Vdc
before I solve my QCX 20M. I can get output only 1.5 ~ 2w maximum
First i observe LPF circuit C25 and C26 (390pf) getting very hot during transmission.
This is my modification.
1. remove 1 turn of L1 and L3 (use only 15 turns) --> power improve abit to ~ 2.5w
2. remove C25 and C26 (390pf) and i replace with 2 series of MLCC capacitor 680pf (because there are in my stock) --> this big improve my power to 5w !!!
I believe?my issue is mismatch at LPF especially?at C25 and C26 (390pf).
thanks group for good knowledge?sharing?and Hans for the grate kits.?
73
Choke E29AHU
during experiment
finally soldering in the right place
output power @12vdc
|
Thanks Jim, I will do this too once mine is built, I am just trying to see/ gather more info if this is actually a problem/ solution to the lower output on 20M....
|
You can test it yourself. ?Just power it up, set the frequency you want and then with it still powered, remove the LCD temporarily. ?Check your power - Hans said and I checked that the QCX will operate with the LCD removed, you just won't be able to see what it's set for is all.
Jim - W0EB
------ Original Message ------
Sent: 11/28/2017 5:23:44 PM
Subject: Re: [QRPLabs] Power output on 20 meters.
HI Gents,
Would any of you be able to test these again with the LCD removed / relocated away from the LPF?
73, Nick VK4PLN
|
HI Gents,
Would any of you be able to test these again with the LCD removed / relocated away from the LPF?
73, Nick VK4PLN
|
Mike;
I wired my 20m QCX, #748, with all wire turns, exactly per the manual and at 12volts, it shows 2.5w to a dummy load.? 73, de Karl, KO8S
On Tuesday, November 28, 2017 12:32 PM, "mike@..." <mike@...> wrote:
Hi All
Results of L1, 2, 3 uH measured values fitted with QRP Labs supplied toriods and 1 turn removed from L1, 2 & 3
?
In situ (still fitted to board)...........
?
L1 = 0.856 (15t)
L2 = 1.028 (16t)
L3 = 0.915 (15t)
?
On Bench...........
?
L1 = 0.868 (15t)
L2 = 1.076 (16t)
L3 = 0.904 (15t)
I have tried Micrometals toriods with very similar results, but the Q factor on the Micrometals is about 30 as against 60 with the QRP Labs ones (but I don't think this makes much difference?).
Note that the inductance will change dependent on tightness of windings - closer tightness = more inductance by a few %. It is also difficult to get the actual calculated values as you are limited to whole turns.Having said all that the output does not change significantly.
The LCR meter I used was a DE-5000 which has a 0 to 20uH range and Kelvin clips with claimed 2.5% accuracy. If you order one from Japan you will probably get stung for VAT, etc.
Bottom Line................
As fitted but with 0.4mm wire...........
?
L1 = 0.80 (14t)
L2 = 0.89 (15t)
L3 = 0.78 (14t)
On 20M and in round numbers ¨C turns as manual = 1 watt output, with 1 turn removed off L1, 2 & 3 = 2 watts and after removing 2 turns off L1, 2 & 3 = 2.8 watts all at 12V input to QCX board.
I am not able to make any output checks except output watts.
I hope this helps those building the 20M version.
73
Mike
G0CVZ
?
|
Hi All
Results of L1, 2, 3 uH measured values fitted with QRP Labs supplied toriods and 1 turn removed from L1, 2 & 3
?
In situ (still fitted to board)...........
?
L1 = 0.856 (15t)
L2 = 1.028 (16t)
L3 = 0.915 (15t)
?
On Bench...........
?
L1 = 0.868 (15t)
L2 = 1.076 (16t)
L3 = 0.904 (15t)
I have tried Micrometals toriods with very similar results, but the Q factor on the Micrometals is about 30 as against 60 with the QRP Labs ones (but I don't think this makes much difference?).
Note that the inductance will change dependent on tightness of windings - closer tightness = more inductance by a few %. It is also difficult to get the actual calculated values as you are limited to whole turns.Having said all that the output does not change significantly.
The LCR meter I used was a DE-5000 which has a 0 to 20uH range and Kelvin clips with claimed 2.5% accuracy. If you order one from Japan you will probably get stung for VAT, etc.
Bottom Line................
As fitted but with 0.4mm wire...........
?
L1 = 0.80 (14t)
L2 = 0.89 (15t)
L3 = 0.78 (14t)
On 20M and in round numbers ¨C turns as manual = 1 watt output, with 1 turn removed off L1, 2 & 3 = 2 watts and after removing 2 turns off L1, 2 & 3 = 2.8 watts all at 12V input to QCX board.
I am not able to make any output checks except output watts.
I hope this helps those building the 20M version.
73
Mike
G0CVZ
?
|
Dave, Kurt,
Hans has said build them as the manual and reduce turns as required.
Those that have what they think to be reliable inductance meters have measured first, their results are posted here.
Those meters which do not go down too low might be used with another inductor in series but always the question is "how accurate?". To be really sure a known standard should be used to check. Too low a value of inductance will appear to work but may not have the designed harmonic rejection. If you wind them with less turns at the start then you will not know if you really needed to.
Some have blamed the capacitors but as Hans has said, if the inductors are wrong then the mismatch can heat them up.
Last week Bob mentioned the MLC500, others have mentioned the LC100A with right-hand connector but although some are good I think these Chinese offerings are suspect. There may be many little companies manufacturing meters that look identical, some are good, others could be poor copies. If someone can give a valid link to where they got one that has tested say 2% accuracy in the QRP Labs range then perhaps you have a chance.
The problem is that one made by a known, reputable company is expensive.
73 Alan G4ZFQ
toggle quoted message
Show quoted text
? ? I have been pondering the same questions as well.? I will be starting my 20m version after Thanksgiving.? As I read the various posts on power output I too wonder if it was due to L1-L4 inductance value variance from what they should be.? I don't have an LC meter so I am planning on blind faith on my build unless I can find an LC? meter that will not break the bank but will do the job.
I¡¯m getting closer to beginning the build on my 20 meter unit.? My
40 meter version is working pretty well, except my power output is
only slightly over 2 watts.? I assume I need to do some adjusting on
L1 through L4.
|
Dave; ? ? I have been pondering the same questions as well.? I will be starting my 20m version after Thanksgiving.? As I read the various posts on power output I too wonder if it was due to L1-L4 inductance value variance from what they should be.? I don't have an LC meter so I am planning on blind faith on my build unless I can find an LC? meter that will not break the bank but will do the job.
? ? I will be curious to see responses to your post.??
Best 73 and Happy Thanksgiving.
Kurt - W2MW
-------- Original Message --------
Subject: Re: [QRPLabs] Power output on 20 meters.
From: "w7aqk" < w7aqk@...>
Date: Wed, November 22, 2017 8:21 am
To: [email protected]
? Hi All, ? I¡¯m getting closer to beginning the build on my 20 meter unit.? My 40 meter version is working pretty well, except my power output is only slightly over 2 watts.? I assume I need to do some adjusting on L1 through L4.? I tried to measure the inductance for each as I built them, but the LC meter I have was struggling to determine that low a value.? So, I don¡¯t know what values I actually ended up with. Reading about all the adjusting that is going on with the 20 meter units makes me wonder.? For those who are seeing improvement in power output, are you getting closer to the values stated in the manual, or is this adjusting the values themselves through trial and error?? If success is getting closer to the values stated in the manual, I may try and find a better measurement tool before installing.? I guess I¡¯m assuming the stated values are considered to be preferable, and that they were determined by calculation rather than trial and error.? Here is another question, and probably a dumb one.? My LC meter has difficulty with low values.? So, what if I put something of low value in series with a higher value that does measure?? Will the difference be more or less correct, thus giving me a read on my lower value component?? I¡¯m guessing the answer is no, or not necessarily, but thought I would ask!!!! ?
|
?
Hi All,
?
I¡¯m getting closer to beginning the build on my
20 meter unit.? My 40 meter version is working pretty well, except my power
output is only slightly over 2 watts.? I assume I need to do some adjusting
on L1 through L4.? I tried to measure the inductance for each as I built
them, but the LC meter I have was struggling to determine that low a
value.?
So, I don¡¯t know what values I actually ended up with.
Reading about all the adjusting that is going on with the 20 meter units
makes me wonder.? For those who are seeing improvement in power output, are
you getting closer to the values stated in the manual, or is this adjusting the
values themselves through trial and error?? If success is getting closer to
the values stated in the manual, I may try and find a better measurement tool
before installing.? I guess I¡¯m assuming the stated values are considered
to be preferable, and that they were determined by calculation rather than trial
and error.?
Here is another question, and probably a dumb one.? My LC meter has
difficulty with low values.? So, what if I put something of low value in
series with a higher value that does measure?? Will the difference be more
or less correct, thus giving me a read on my lower value component?? I¡¯m
guessing the answer is no, or not necessarily, but thought I would
ask!!!!
?
|
On Sat, Nov 18, 2017 at 01:56 pm, G0DZB wrote:
Are you not concerned that your passive filter seems to have gain ?
PeterO
G0DZB
PeterO, Andy, I mainly wonder if the SHAPE and cut off point of that curve still is as it shoud be after modification.? Just skipped that boring calibration, but never assumed having invented the perpetuum mobile. 73 Wolf
|
On Sat, Nov 18, 2017 at 01:56 pm, G0DZB wrote:
Are you not concerned that your passive filter seems to have gain ?
I was going to write those exact words, then scrolled down to discover that you had beaten me to it. 73 de Andy
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On Sat, 2017-11-18 at 13:36 -0800, Wolf DL1GWW wrote: Hi Anatoly, thanks for reply!
The first picture shows the sweep with C29 on board, in the picture
below with C29 removed: Are you not concerned that your passive filter seems to have gain ? PeterO G0DZB
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Shirley Dulcey KE1L
Fred Piering WD9HNU
Nick VK4PP
Jim Sheldon
Kurt Zimmerman