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Transmit Output Power (CW)
#v5
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I've collected all my parts to do Allison's transmit chain modifications (BFR106, 2N2222, 11 ohm resistors...).? I'm ready to go... but I wanted to QC my output power first.? Now, I have noticed on 40 meters (where I spend most of my time), that the output power is low, so now that I finally have a power meter, I went ahead and tuned RV1 while transmitting into a dummy load.? I tuned RV1 to get 12W output on 3.500 MHz, and then checked the output power across the rest of the bands.? This is what I got... is this representative of what other people have seen?? I know I'd seen reports of crazy low output power (<1 W) on 10 meters, which I did NOT observe here, obviously.? (Note, all of these were done with CW.)
Any thoughts?? (a) Are these typical of what others have observed?? (b) What can I expect from the transmit modifications, relative to this?? Higher output on 30, 20, 17? Thanks! -Rob KC4UPR PS - Random aside.? So I am using KD8CEC firmware version 1.2.? I noticed something weird on 40 meters... If I tune to exactly 7.000.000 MHz, or lower, in the 40 meter band, I hear the T/R relay switch and the display indicates in CW transmit, but there's 0 W output power.? But if I tune to 7.000.010 or higher, it's fine.? It's kind of like it's enforcing transmit restrictions, except that the ONLY place that it seems to do this is on the bottom end of 40 meters!? I've tried to trace code behavior for the band limiting, and could not identify anything that would make this happen.? Has anyone else observed this??? |
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Joe Puma
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On Mar 11, 2020, at 10:13 PM, Rob French (KC4UPR) <kc4upr@...> wrote:
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why? he already did the test with CW which will give the maximum power out vs a whistle which will vary and may have a complex signal component and reduce how much power you see on a non-peak reading meter. in radio shops we always test in either CW or FM for max power out, and then in AM to set the carrier level. Matthew Chambers, CBT, NR0Q Owner/Engineer M Chambers Communications Engineering LLC PO BOX 855, Moberly, MO 65270 Mobile (660)415-5620 On Wed, Mar 11, 2020 at 9:57 PM Joe Puma <kd2nfc@...> wrote:
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Joe Puma
¿ªÔÆÌåÓýBecause CW and SSB use different output stages and the mod he¡¯s doing is for SSB. I, sure someone here can explain it better. ?If you don¡¯t want to use a varing whistle use a 1khz tone from your iPhone. (Youtube video). The uBitx is not like other radios. ?Joe KD2NFC On Mar 11, 2020, at 11:05 PM, Matthew Chambers NR0Q via Groups.Io <mchambers@...> wrote:
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Looking at the schematic for the V5, I understand that the way it works is that the CW key line (DC) is fed into mixer 1 along with the Clock #2 signal.? The output signal path from this is then through the 45 MHz low pass filter (I think that's what it is on the schematic) and then into the normal transmit power output chain through Q90.? Isn't that the same as CW?
Regardless, for testing it in SSB, could I use the tune output from a digimode program such as Fldigi? |
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Joe,
To the best of my knowledge, the v5 boards have the upgrades in the sections prior to the first mixer (upgrading the 2n3904 to BFR93W) related to SSB performance.? The upgrades that are not done are in the driver and predriver stages where the 2n3904s are suggested to be replaced with 2n2222a or better devices.? Those sections are the same for both CW and SSB and can be modified for more consistent performance per Allison/KB1GMX in messages over a year ago.? The original work was done on the v3 and v4 boards, which then brought up the harmonics and spurs issues.? This lead to the v5 fixes that solved them through both redesign of the output filter sections of the board and the addition of a 45 MHz low pass filter between the 45 MHz IF stage and the first mixer T2.? The 40 meter power "dip" has not been addressed.? I believe that the v5 boards are not as bad as some of the prior boards.? I conjecture that one of the issues was incorrect turns or spacing of the 40 meter lpf inductors that seems to have reduced the problem, but not eliminate it. To get more information of what has been tried to balance power out across bands I would read through the 331 messages that start with this one from Allison: Message #49729 /g/BITX20/message/49729 There has not been a significant change to the uBitx in the stages from Q90 through the output lpf, so there is some opportunity to improve, though the output that Rob listed is not as bad as some that have been posted on this message board. All, Above are just suggestions, conjecture, and beliefs on my part.? Please take that into account and please excuse any errors or misconceptions on my part. 73 Evan AC9TU |
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Joe Puma
¿ªÔÆÌåÓýThanks Evan. I have done the power mod on V3 and also used different sized bias resistors which worked better for my board. ?My power out on CW is slightly higher then on SSB and it¡¯s not because of the CW carrier. My emails are along the 331 emails as I was asking questions so I am familiar with Allison¡¯s mod and comments about the differences between power out on CW And SSB. I know if you¡¯re going to do the mod. It¡¯s best to test your SSB out and use the CW carrier.?Joe KD2NFC? On Mar 12, 2020, at 9:02 AM, Evan Hand <elhandjr@...> wrote:
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Joe Puma
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On Mar 12, 2020, at 9:16 AM, Joe Puma via Groups.Io <kd2nfc@...> wrote:
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Rob
your as-is numbers are not bad on CW.? (some of us would gladly trade board with you - actually mine is somewhat simpler - except I had an even larger dip on 40m, that I corrected with a capacitor change pointed out by Asshar).? remembering each S-unit on receive is approximately 6 dB - I would not myself want to change anything.? (if you really really want a flatter PA - you could possibly buy the 10 watt PA kit from QRP-Labs, and use it instead of this portion of the ubitx - but funny thing when we get good solar flux in 4-6 years from now - you might be using a uBitx v12 or a QSX v3 ....) SSB needs to be evaluated separately, using an audio oscillator as an input.? the SSB path uses the 45 MHz mixer 'as a mixer.'? CW is different because it puts a bias onto the mixer, and then leaks through a signal at the intended RF (no mixing!).? keep in mind the driver and PA are common to both CW and SSB - the overall behavior should track but you may experience different degrees of dip and peaking.? with the circuit board as is - you can only do so much with the overall behavior of the PA and tweaking of the driver frequency response.? you might work very hard to get a better measurement into your power meter on 40m that the operator on the other end will not even notice.? 73 Curt |
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We have three power meters. None of them read the same. On one it reads 5 and the other 20 on some bands. Which is real?
Have 4 ubitx and the best comparison is to compare between the units. The reality is they sound the same to stations I work. I doubt if they are identical but are "nomal". Don't take your working radio and make it not work. The forum is full of those. I have fixed a number of them and the first thing I do is to make the radio stock.? If you do decide to work on it change one stage of transistor and bias at a time and test. There are pitfalls. burn up a trace and find out. -- 73 Dave |
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jim
Just a random thought ...do you have any way to check for harmonics/spurs at these settinjgs? while tuning for "maximum smoke" is one way to do it, what you are measuring with the power meter is ..along with the fundamental frequency, ALL the spurs/harmonics/random trash being radiated...would be great to see some measurements of them before the modding as well as after Jim
On Thursday, March 12, 2020, 2:13:41 AM UTC, Rob French (KC4UPR) <kc4upr@...> wrote:
I've collected all my parts to do Allison's transmit chain modifications (BFR106, 2N2222, 11 ohm resistors...).? I'm ready to go... but I wanted to QC my output power first.? Now, I have noticed on 40 meters (where I spend most of my time), that the output power is low, so now that I finally have a power meter, I went ahead and tuned RV1 while transmitting into a dummy load.? I tuned RV1 to get 12W output on 3.500 MHz, and then checked the output power across the rest of the bands.? This is what I got... is this representative of what other people have seen?? I know I'd seen reports of crazy low output power (<1 W) on 10 meters, which I did NOT observe here, obviously.? (Note, all of these were done with CW.)
Any thoughts?? (a) Are these typical of what others have observed?? (b) What can I expect from the transmit modifications, relative to this?? Higher output on 30, 20, 17? Thanks! -Rob KC4UPR PS - Random aside.? So I am using KD8CEC firmware version 1.2.? I noticed something weird on 40 meters... If I tune to exactly 7.000.000 MHz, or lower, in the 40 meter band, I hear the T/R relay switch and the display indicates in CW transmit, but there's 0 W output power.? But if I tune to 7.000.010 or higher, it's fine.? It's kind of like it's enforcing transmit restrictions, except that the ONLY place that it seems to do this is on the bottom end of 40 meters!? I've tried to trace code behavior for the band limiting, and could not identify anything that would make this happen.? Has anyone else observed this??? |
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Andy_501
¿ªÔÆÌåÓýHere are a couple of tone clips that might be useful; 700-1900 is
2 tone? 300 and 3000 are voice BW max & min. I use another SDR
spectrum display to check spectral purity for things like
harmonics. depending where you feed it into system you might have
to fashion an atten pad cheers
On 2020-03-11 10:05 p.m., Matthew
Chambers NR0Q via Groups.Io wrote:
300hzSpectrumBase_31.25mv.wav
300hzSpectrumBase_31.25mv.wav
700-1900-2tone_31.25mv.wav
700-1900-2tone_31.25mv.wav
3000hzSpectrumBase_31.25mv.wav
3000hzSpectrumBase_31.25mv.wav
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Jim, no, I don't really have a way to check for that.? I suppose I could use my SDR dongle as a poor man's spectrum analyzer??? See what other spikes I get in the spectrum when I transmit?
I will note that, at the low end of 80 meters, prior to turning up RV1, I was only getting ~6.5W, so I'm wondering if my uBITX wasn't quite adjusted right from the factory... I wasn't getting 8 W anywhere.? Although, that probably also gets to Dave's point about different power meters, different measurements. |
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If you have a decent amp meter you can adjust RV2 and RV3. Don't try and set them by ear. Review. the procedure on line. All three RV adjusters adjust the final power out be it ditties or voice.? I got one unit that was weak on transmit and turning up RV1 brought it up to spec. I have a spread sheet that has the approximate RF voltage at each transmitter stage as collected by my 30 year old scope. You would want an oscope to compare. Basically you see that each transformer decreases the voltage substantially but the 3 transistor array more than makes up and by the time it is to the next? transformer it is stronger than it was when it entered the prior stage.? Personally I would not want to do a two tone test at this point.? If you have done any modifications you are not in a position to see what if any difference they are making. Best return to stock to make that as good as possible.? If yours is a v5 it should have the improved transistors in it. No? You should verify.? I looked through this post and was not sure of the model version.? -- 73 Dave |
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jim
Well ...anything you've got is better than nothing ...back in the old days, folks used a wave-meter (gdo in diode position) to check for spurs/harmonics ..was hoping for some before/after measurements...ah well thanks, Jim
On Friday, March 13, 2020, 1:59:53 AM UTC, Rob French (KC4UPR) <kc4upr@...> wrote:
Jim, no, I don't really have a way to check for that.? I suppose I could use my SDR dongle as a poor man's spectrum analyzer??? See what other spikes I get in the spectrum when I transmit? I will note that, at the low end of 80 meters, prior to turning up RV1, I was only getting ~6.5W, so I'm wondering if my uBITX wasn't quite adjusted right from the factory... I wasn't getting 8 W anywhere.? Although, that probably also gets to Dave's point about different power meters, different measurements. |
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I do have a V5 board.? To be clear, I have not yet made any modifications to the transmit chain... the only thing I have done is adjust RV1 to increase the output power on 80M to about 12W.? Before I did that, the pot was set at about half way, so it would be easy enough to turn RV1 back to a half-turn, and it should pretty much be what it was from the factory, +/- a few tenths of a watt.? I could then take reasonable "before" measurements.
I can't tell by looking what Q90 is (tiny little thing...), but based on the official V5 schematic, it should be an SMD 2N3904.? The rest of the pre-driver/driver transistors (6 of them) are all 2N3904, by the looks of them. My power meter is built into an automatic antenna tuner designed for up to 150W.? So I'm sure it's not super accurate. Thanks for all the feedback! -Rob KC4UPR |
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Mark - N7EKU
Hi Rob,
It would be interesting to see "before" measurements. One trick on viewing SMD parts is to take a good picture with a smartphone or digital camera and then zoom in to view the fine print.? SMD parts typically don't have real names on them like "2n3904" but have codes.? There are code lists on the web to help translate them though. To check power at lower power levels (like the ubitx) you can use a diode RF probe.? Easy to make from scratch or as a kit.? Some QRP dummy loads have them built in (e.g. Elecraft, QRPGuys, QRP-Labs all have them). If I remember correctly, I think changing Q90 and its biasing makes the biggest different in evening the output. 73, Mark |
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Alrighty... I finally got around to a couple of things:
(1) Building myself a "digital dummy load" using my QRP Labs 20W dummy load and an Arduino.? I calibrated it against my ATU's wattmeter, which isn't probably a great source, but I used the output power of my RS-HFIQ, which I feel is pretty accurate at 5W +/- a little. (2) Reset RV1 to the "stock" configuration, about mid-range.? Also tweaked my BFO setting to make sure I was getting some power out with both 300 Hz and 3000 Hz audio. (3) Hooked up the mic input to my computer so I could play those 300, 3000, and 700-1900 Hz tone wave files into it. Here are my results in the "essentially stock" configuration.
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_Dave_ AD0B