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4.3 Power output vs supply voltage for QDX-HB ??? #qdx
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Mike KK7ER
It looks like section 4.3 of the 1.16 and 1.18 construction manuals have not yet been updated to provide the expected power output vs supply voltage for the high band version of the QDX.
I'm seeing (3:2 T1 into a dummy load):
What is the expected performance? Is there an output power optimization procedure (similar to the QCX)? 73, Mike KK7ER |
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Jim Strohm
Mike,
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This may be the natural drop-off of the BS170s' power as they approach their fT. You might try a FET with a higher fT like J310s. 73 Jim N6OTQ On Sat, Jan 14, 2023 at 10:38 PM Mike KK7ER <groupio@...> wrote:
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Bojan Naglic
Hi,
My QDX at +12V, taking into account cable attenuation=0.2dB, LPF usage: 0(20m), 1(17m), 1(15m), 2(12m), 2(11m), 2(10m): 20m, 3.9W 17m, 3.7W 15m, 3.3W 12m, 3.3W 10m, 3.5W 73 Bojan S53DZ |
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On Sun, Jan 15, 2023 at 12:29 AM, Jim Strohm wrote:
You might try a FET with a higher fT like J310s.Besides being a much smaller (current-wise) and lower-breakdown voltage device, the J310 is a depletion mode FET, while the BS170 is enhancement mode, so for sure not a drop-in replacement. 73, Don N2VGU |
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Alan G4ZFQ
On 15/01/2023 15:55, Donald S Brant Jr wrote:
so for sure not a drop-in replacement.This has been discussed before. The answer has always been that there is no better device for the QRP Labs designs. The optimisation process is the same for all designs. One question, does the power meter read accurately? It seems some peoples power readings never get to match others. 73 Alan G4ZFQ |
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Mike,
My 9V high-band QDX has approximately the same power per band as yours. I was dissapointed with the 10M performance as well. Didn't check 11m since can't TX there. Gary W9TD |
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Michael Black <mdblack98@...>
Unless you are measuring power with an oscilloscope or a decent, calibrated power meter like an LP-500 power measurements are a crap shoot.
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Wide variation in accuracy by band is known for a lot of power meters. Mike W9MDB On Sunday, January 15, 2023 at 10:33:02 AM CST, Gary W9TD <w9td@...> wrote:
Mike, My 9V high-band QDX has approximately the same power per band as yours. I was dissapointed with the 10M performance as well. Didn't check 11m since can't TX there. Gary W9TD |
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Hans Summers
Hi Donald, all MOSFETs don't have fT. Capactiances are the limiting factor but there shouldn't be that much difference between 10, 11 and 12m. Not very reasonable... I suspect the 10/11/12m LPF design may be a little too close to 10m so variations in component tolerances and toroid winding styles could put some unwanted attenuation in at 10m. I'm normally getting 3.5-4W on 10m but since several of you have reported low output on 10m I suspect the LPF may need a little alteration. On my ToDo list... 73 Hans G0UPL http://qrp-labs.com https://www.buymeacoffee.com/g0upl -------- Original message -------- From: Gary W9TD <w9td@...> Date: Sun, Jan 15, 2023, 7:33 PM To: QRPLabs@groups.io Subject: Re: [QRPLabs] 4.3 Power output vs supply voltage for QDX-HB ??? #qdx Mike, |
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I don't think it is the LPF as the current drain on 10M transmit is noticeably lower than other bands.
Gary W9TD |
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Muhsin TA1MHS
hi
Band QDX1 QDX2 (both V4)
20m 3.7W 4.0W
17m 2.3W 2.7W
15m 2.6W 3.3W
12m 3.2W 3.0W
11m 3.1W 1.3W (both toroids are same, I don't understand this)
10m 2.2W 1.2W
SUPPLY 12 6V
To QRP Labs dummy load's Volt
ATU-10's Wattmeter
I think LPF2 frequency must be pushed a little bit higher
73 muhsin TA1MHS
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I was looking at waveforms in the PA. Looking at the drain voltage, the PA FETS turn on in the middle of the portion of the cycle when they should be off. I notice this on 17, 12 and 10-meters. On 20, there is only a slight dip and on 15, I see no dip. This turn-on lowers the power out and more so on 10-meters where it is a larger portion of the cycle. At the T1 transformer output, I see the dip in the waveform, but not all the way to zero like on the primary side, on all bands but 20.
One possible cause is the gate drive ringing that I can see. Another could be an enhancement of the second harmonic due to the output low-pass filters.
I am using a Tektronix P6201 900MHz bandwidth active probe with a 10X tip having only 100k and 1.5pF of loading with a Tektronix 350MHz bandwidth 485 'scope. Gary W9TD |
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Hans Summers
Hi Gary > I don't think it is the LPF as the > current drain on 10M transmit > is noticeably lower than other > bands. I don't think this observation rules out the LPF response as the culprit. I will investigate further as soon as possible. 73 Hans G0UPL http://qrp-labs.com https://www.buymeacoffee.com/g0upl -------- Original message -------- From: Gary W9TD <w9td@...> Date: Sun, Jan 15, 2023, 8:38 PM To: QRPLabs@groups.io Subject: Re: [QRPLabs] 4.3 Power output vs supply voltage for QDX-HB ??? #qdx I don't think it is the LPF as the current drain on 10M transmit is noticeably lower than other bands. |
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Oleh I2/UY2ZA
Gary, if you have such a measuring technique, can you see the signal at the output of the output transformer? Without LPF.
Of course, loading it into 50 ohms. We would know the real delay without the filter. -- 73, Oleh, UY2ZA |
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Oleh,
I did look at T1 output but the LPF can not be bypassed or I don’t want to modify it to do so. Sorry, Gary W9TD |
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Hans,
I think you are right about the LPF. I placed a small variable cap across the T1 primary and peaked the 10-meter power output from 1.9 Watts without the capacitor to 2.9 Watts with it set to 52pF. Unfortunately, the capacitor reduced power on all the other bands. Gary W9TD |
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Muhsin TA1MHS
hi
Band QDX1 QDX2 QDX2 (now Modified) all Ver4
20m 3.7W 4.0W 4.0W
17m 2.3W 2.7W 2.7W
15m 2.6W 3.3W 3.3W
12m 3.2W 3.0W 3.5W
11m 3.1W 1.3W 1.6W L4 8 turns now L10 9 turns now
10m 2.2W 1.2W 1.5W 247uH 299uH
SUPPLY 12 6V
To QRP Labs dummy load
ATU-10's Wattmeter
all Cs checked, values within %5
L4 and L10 measured/trimmed with Mini 1300 antenna analyzer's L/C Meter
something else is wrong :(
73 muhsin TA1MHS |
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Bojan Naglic
Hi,
My experience with such cases was always the LPF too low cut-off frequency. Also with the QDX high band I had to spread the turns on the toroid a bit to get 15m fully covered. This way I got +2dB! I have checked the LPFs with a VNA (in-circuit from T1 secondary to BNC) to see the issue. It is of course not an absolute measurement but it gives the filter curve. 73 Bojan S53DZ |
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Steve Z
I'm also seeing low power for the higher bands on the High-band QDX. I tried using the nanoVNA to measure the three LPFs. My test setup is not great, but the filters seem to look pretty good. Here are the three filters in the order low (20 meters), medium (17 and 15 meters), and high (12 and 10 meters). Maybe the high filter could stand to be shifted to higher frequencies just slightly.
Steve N9SZ |
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Brian
I've just finished building my QDX-HB and first results are that the power output on 10m is quite a bit down.
With 9 volt supply, the output on 20m is 3.9W and on 10m drops to 2.5W. The total current drain is 800mA on 20m and 700mA on 10m from the bench power supply. I was intending to measure the capacitors before building. It is very difficult to read the marked values. My LC meter has packed up so I didn't. There is a wide tolerance on the toroids anyway so I guess it needs the NanoVNA/Tiny SA to improve it. Does WSJT-X allow you to transmit (into a dummy load) out of band? 73 Brian VK4BAP. |
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Bojan Naglic
Hi,
This is my in-circuit approximate measurement that helped me to improve the QDX's 17m/15m LPF and get some more power out at 21MHz band. And the same improvement at the RX. Again, it is certainly not a precise measurement in dB of LPF I.L., ripple or f-cutoff. But gives an information what is going on. 73 Bojan S53DZ |
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