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Hi all. I just finished my first QCX build for 20m and I’m curious about the power output. I’m currently getting around 2.5 watts RF output based on the readings provided by the QCX menu 9.2. After reading some other threads, it seems it’s possible to increase the power output by removing turns from the L1, L2, and L3 toroids. My question is: what sort of increase I should expect? I’m trying to decide if it’s worth the trouble to do the modification if I’m only going to get a few mW difference. Any other suggestions are appreciated.?
de KT4RK?
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I removed 1 turn each and got about an additional 500mw.
73 Vince N1VIN
On 3/28/2019 1:50 PM, KT4RK wrote:
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Hi all. I just finished my first QCX build for 20m and I’m curious
about the power output. I’m currently getting around 2.5 watts RF
output based on the readings provided by the QCX menu 9.2. After
reading some other threads, it seems it’s possible to increase the
power output by removing turns from the L1, L2, and L3 toroids. My
question is: what sort of increase I should expect? I’m trying to
decide if it’s worth the trouble to do the modification if I’m
only going to get a few mW difference. Any other suggestions are
appreciated.?
de KT4RK?
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I went ahead and took off two turns from L1 and L3 and it made no difference at all. I guess I need to keep fiddling with it.
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I too, probably am getting about 2.5watts output on my QCX20, for more power, I use this to drive my HFpacker QRP linear amp.? My 3-el tri-band Yagi up on the tower, helps a lot too. This combo does an excellent job!? Since my QCX20 is working great, I am not going to fool with it!? 73, Karl, KO8S
On Thursday, March 28, 2019, 04:52:52 PM EDT, KT4RK <Kt4rk.tn@...> wrote:
I went ahead and took off two turns from L1 and L3 and it made no difference at all. I guess I need to keep fiddling with it.
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I think this came up in a previous discussion. ?At one point there was some inferior caps that ware provided as part of the kit. ?When I built my QCX 20 I opted to buy new caps for C25-C28 and install them instead of installing the ones that came with the kit just in case becuase some (not all) people were experiencing this problem with low power. Here is a link to my original post: /g/QRPLabs/topic/29337518#30515?
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I have already installed the caps, so I may pull them and replace them just to be on the safe side. I took turns out of L1-L3 and my RF output is still at 2.29 watts on my battery. I’m not expecting 5w output, but would like to get at least 3w out of it.?
I’m a novice at electronics and don’t have any testing equipment other than a digital multimeter, plus I’m learning as I go. I appreciate the feedback thus far. ?
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think I have narrowed the issue to the caps at C25 and C26. They are supposed to have a value of 390pF, but when I tested a spare one that came with the kit, it measured 55pF. ?I already ordered some new ones, so I will update once they are installed.
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Did you check the markings on the caps fitted. Component quality
is very good these days. Did you check your tester against a known
good capacitor. What are you using to test capacitors, is it a DVM
with a capacitance range or a dedicated LCR tester that uses a RF
signal.
Electronics manufacturers have to ensure that components they use
are within the specified tolerance range, they do not want to have
an entire production line scrapped because the 390pF capacitors
are 55pF. The wholesale suppliers don't have two stocks , one for
commercial users and one for small quantity buyers and the
quantity that Hans buys would put him into the large buyer
category.
As my eyesight is not as good as it was 60 years ago, I double
check all components before fitting and I have NEVER found a new
modern component that is outside the tolerance specified.
On 3/31/2019 7:19 PM, KT4RK wrote:
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think I have narrowed the issue to the caps at C25 and C26. They
are supposed to have a value of 390pF, but when I tested a spare
one that came with the kit, it measured 55pF. ?I already ordered
some new ones, so I will update once they are installed.
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Just to be on the safe side, I ordered new silver mica's for C25 thru 28 to go in my QCX 20 if it ever gets here.?
73 Jack KZ5A
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I believe there were not supposed to be 'spares', but parts for other bands. Was the loose one you tested actually marked as a 390 pF cap? What did you measure it with?
I presume what you stuck in c25 and c26 are properly marked? When you yank them, please measure and report those also, as that might also help other builders, as well as Hans and others when offering assistance.
Regards, Dave N3AC
think I have narrowed the issue to the caps at C25 and C26. They are supposed to have a value of 390pF, but when I tested a spare one that came with the kit, it measured 55pF.? I already ordered some new ones, so I will update once they are installed.
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I tried to be pretty meticulous when building it. I definitely had one spare cap in addition to the others for different bands and the kit was actually short two of the 10uF electrolytic caps that are installed in step 3.40 of the manual. I’ve tried to see if I missed one somewhere.?
I just pulled the two “391” caps. One I destroyed in the process, the other came out in one piece and it measured 26pF on my digital multimeter that has a setting for measuring capacitance. Maybe my meter is whacked, but I’ll check the replacements to compare before I install them.
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Like others have mentioned, you may want to check capacitance at RF... if you can't do that, I'm sure there are several hams in the Knoxville area that would love to help you out.
I followed directions for my QCX-40, but now that it is tuned... I may short out/jumper (instead of removing) D3 (the reverse-polarity protection diode); that'll raise the voltage to my rig a little. I'm currently using a Tripp-Lite which regulates at about 13.5V...
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For me the protection the diode offers far outweighs the slight received signal improvement ( not measured power out) you get from bypassing it.
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I understand. I choose to bypass it if I'm going hiking...
On Mon, Apr 1, 2019 at 9:24 PM Chopper < bob@...> wrote: For me the protection the diode offers far outweighs the slight received signal improvement ( not measured power out) you get from bypassing it.
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Don't have a QCX, haven't tried it.
But I'd consider feeding 12v into Q6 (and thus the BS170's) straight from the battery,
leave everything else to run from the protection diode.
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On Mon, Apr 1, 2019 at 06:54 PM, Dave & Ruth Haring wrote:
I understand. I choose to bypass it if I'm going hiking...
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?
On Mon, Apr 1, 2019 at 9:24 PM Chopper < bob@...> wrote: For me the protection the diode offers far outweighs the slight received signal improvement ( not measured power out) you get from bypassing it.
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it measured 26pF on my digital multimeter that has a setting for measuring capacitance. Most meters of this type are useless, especially at low capacitances. Even a dedicated capacitance meter should be viewed with suspicion unless you have checked the calibration. (Unless it is of guaranteed accuracy.) 73 Alan G4ZFQ
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Just like I said in my previous post several days ago.
Amen Alan.
On 4/2/2019 7:59 AM, Alan G4ZFQ wrote:
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it measured 26pF on my digital multimeter
that has a setting for measuring capacitance.
Most meters of this type are useless, especially at low
capacitances.
Even a dedicated capacitance meter should be viewed with suspicion
unless you have checked the calibration. (Unless it is of
guaranteed accuracy.)
73 Alan G4ZFQ
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Although such meters are not highly accurate, it's rare for one to be
off by nearly an order of magnitude.
I hope it's not a case of misreading the part values. An OLD capacitor
that says 390 on it, such as you might find in your junkbox, might be
a 390pF capacitor, except that they would have called it 390uuF
(micromicrofarads) in the day. But a NEW capacitor that is labeled 390
is a 39pF capacitor; the final digit is a multiplier, and the 0 says
to add no zeroes to the end.
For whatever reason, nanofarads never caught on the US though they are
used elsewhere. On this side of the pond the common bypass capacitor
is 0.1uF, but a British builder might call it 100nF instead. Values of
1000pF up to just shy of 1uF are usually given as fractional
microfarad values, so other popular bypass values are .001uf (1nF) and
.01uF (10nF). Similarly we don't use millifarads, so a really big
capacitor might be 10,000uF rather than 10mF. You don't see full
farads used until you get up into supercapacitor territory, so that
10mF part would NOT be referred to as 0.01F, but a 470mF
supercapacitor would be identified as 0.47F.
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On Tue, Apr 2, 2019 at 2:59 AM Alan G4ZFQ <alan4alan@...> wrote:
it measured 26pF on my digital
multimeter that has a setting for measuring capacitance. Most meters of this type are useless, especially at low capacitances.
Even a dedicated capacitance meter should be viewed with suspicion
unless you have checked the calibration. (Unless it is of guaranteed
accuracy.)
73 Alan G4ZFQ
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Your comment on missing 10u capacitors makes me think you may have built a Rev 4 board and kit using Rev 3 instructions.
Rev 4 changed two 10u electrolytics at C21 and C22 to 1u capacitors.? Obviously you have fitted something, as you have a working QCX but you may well find that two of your 'spare' capacitors are the 1u intended as C21 and C22.? Ceramics would be labelled '106' .
This may affect clicks and thumps on switching and keying, but isn't related to your power output question.?
I get 2w out of my QCX-30 on 13.8v which some may think a bit low.? I may have a look at that later, but for now, I'm just getting on with using a great little rig.
Good luck
Chris G4CWS
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Correction to my last message - ceramics should read '105'.
Chris
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KT4RK
N3MNT
Shirley Dulcey KE1L