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Re: More help if possible please.
Hello to all, I reinstalled BAP on my Pi4+ and it is tx'ing fine. I haven't managed to sort out Conky yet but that is the plan for the morning along with a try at a fresh install of BAP for the 3B+. I am pretty sure that I am missing an essential tweak with the 3B+, the (fairly good) Dell laptop (running Ubuntu 22.04) and the Inovato Quadra . Are there any obvious stuff that may have flown by? TIA. 73, Tryg -- |
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Re: QCX+ Variable Output Power for QRPp Operation
John, I made the mod mentioned above on an old 20 meter Classic QCX I use for experimenting. I fed the Emitter of Q6 with?a separate variable voltage and left the rest of the radio running at 13.8 volts. I varied the voltage to Q6 from 12v down to 5v. Harmonics looked good on the spectrum analyzer all the way down. I got the following output powers: 12v ? ? ? 3.6w 11v ? ? ? 2.9w 10v ? ? ? 1.9w 9v ? ? ? ? 1.2w 8v ? ? ? ? 0.5w 7v ? ? ? ? 0.2w 6v ? ? ? ? 0.012w 5v ? ? ? ? 0.001w I'm sure your results will vary, but it seems like a workable solution if you want to modify the rig. Otherwise, the external attenuator is a good way to go to keep from modifying anything.? 73 .. .Ron On Wed, Jun 21, 2023 at 9:52?AM Don VE3IDS <ve3ids.don@...> wrote:
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Re: QCX+ Variable Output Power for QRPp Operation
The attenuator kit has a single bypass button that can be used for receive. Not automatic but usable.? 72 Don ve3ids? On Wed., Jun. 21, 2023, 12:41 p.m. Bruce Akhurst, <bruce@...> wrote:
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'Morning Dave
It shows -7 however I am not sure how that is based. Here's the produced chart: Below is the original on this unit: I'm pretty sure that these displays are meant to be just relative measurements since the amplitude parameters seem to change with various settings. The proof was the bench results. Those I can control the conditions. On-the-air performance is now quite nice, I am hearing the weak ones and the normal background noise. The only artifacts present are the ones that I had before the modification but, then again, I am in a rural area where I can expect to be able to sneak by without a receive band-pass filter. 72, Don |
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Re: QCX+ Variable Output Power for QRPp Operation
"KM3D - Harry
5:53am???#103985???
....? ?I also wonder what the output level would be with 7 volts running the radio. ? I did a few tests as I to set up my 20 metre QCX+5W.? ?On 9.1V? in? (so less than 8.7V via the protection diode and into? the PA modulator Q6 ) and still got a little over 3 watts out for a the long term beacon.? (it?lasted around 5,000 hours (the PA was still fine) so that should cover quite a few QRP activations) In testing also noted 8V in (7.6V after the diode) still produced 2.4Watts ? To achieve under a watt is going to to require a pretty low PA voltage (nearer 5 than 7 ? ) but I would not go there without a spectrum analyser to see what happens with the BS170 gates 'over driven'.? At some point it will likely get hot or nasty or both? ? I don't understand the 'add an attenuator' suggestions unless you don't care about receive losses ?? |
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Upon completion of my QMX (#331) build I found that the sensitivity on 20 meters to be quite poor, about -92 dBm (5.6 microvolts) for a Minimum Discernible Signal. A topic soon appeared on the forum regarding this as a design problem so I entertained myself otherwise and waited for someone to find a solution. Since there has yet to be a solution proffered I decided to try the obvious solution of replacing C403, a 22 pF capacitor in the band pass filter, with a 16 pF value. That seemed to be what a ratiometric guess would suggest. Nope! The band pass response did indeed get closer but the 14 MHz frequencies were still highly attenuated. A 10 pF capacitor did little better but confirmed that the tapped inductor ( L401) and the associated parasitic capacitances formed an effective trap for the entire 20m band. ? It occurred to me that the simplest solution would be to just bypass the 20m band pass filter entirely. I live in a rural area with no broadcast stations or other strong HF signals. If I needed a band pass filter then I could add one externally or try to wedge in one separate from L401. ? I removed the tap at the 19th turn of L401 from the solder connection, soldering the two conductors together so to effectively remove the tap from the coil. I then removed C403. I installed a 1 nF (.001 uF) 0805 sized capacitor from the input signal side of C402 (the end shared with C403, C401, and C404) to the previously vacated solder pad of the removed tap. I positioned it a bit diagonally, reflowed the solder at the C402 pad so that it fastened the new capacitor. The other end was then soldered to the pad where the L401 19th turn tap used to reside. ? Progressing to the Step 8 tests, I confirmed continuity from IC3 pin 9 to pins 3, 4, and 5 but not 6. Visual inspection confirmed that no potential short circuits had been created. ? The results have been satifactory. MDS is now -121 dBm (0.2 uV) which is comparable with the other four bands. No new birdies or images. No overloads. Just a 29 dB improvement in receive level. Terrestrial, solar, and galactic noise are now all stronger than the weakest signal that I can detect. Operation on all other bands were unaffected. ? If new builders want to duplicate this fix might avoid making the 19th turn tap on L401 and not install C403. The value of the new capacitor is not critical, it just needs to block the DC bias but pass the 14 MHz receive signal when that band is selected. It could be a leaded part, placed from the hole at the input end of the C403 position to the hole where the 19th tap was supposed to go. |
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Re: QCX+ Variable Output Power for QRPp Operation
Here is a low priced attenuator kit.? 73 Don ve3ids? On Wed., Jun. 21, 2023, 10:59 a.m. Chuck - K3FLN via , <chuck.salmon=[email protected]> wrote: John, |
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Re: QMX help - damaged SMD capacitors
#problem
On Tue, Jun 20, 2023 at 09:46 PM, MattW wrote:
how would you recommend repairing the solder pads and replacing this component L202?I modify and repair boards routinely.? The pads don't need repair, just bridge them with wire.?? I would obtain some fine gauge wire, I use wire-wrap wire or single strands from stranded wire and tin it, carefully scrape the solder mask (#15 scalpel blades work best) from the ends of the remaining traces and tin them.? Any undamaged part of the run is OK.? Use low-melting point solder if you have it and go easy on the heat to minimize heating of the damaged traces to avoid them lifting. Lap solder the wire, first to the replacement L202 ends then, after forming/trimming the leads, to the tinned traces.? Measure to ensure continuity and stick the wires and component down with cyanoacrylic (Krazy-type) adhesive.? Done.?? We used this exact technique to repair PCB traces for space flight hardware except using fancy $pace grade low-outga$$ing adhe$ive$. 73, Don N2VGU |
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Re: QCX+ Variable Output Power for QRPp Operation
John, if you are going to do this, I would recommend using a small variable power supply like one of the many made by companies like DROK. They are small enough to easily fit inside the QCX+?case. You will want to go with one that has been shown not to cause issues with noise in your receiver. Connect the input of the supply to the incoming 12v line. Open the circuit to Q6 where Colin indicates with the yellow X and connect the power supply output to that terminal (emitter) of Q6. Find the voltage adjustment potentiometer?on the supply and remove it. Connect 3 wires from the holes it was in to an outboard pot that you can easily?mount on the rear panel of the QCX+. Then you can adjust the power from top to bottom. You might want to add a resistor in series with the low side outer leg of the pot to define a bottom end for the voltage range, or at least do some testing to show when to stop reducing it. It would be a good idea to watch the output?on a spectrum analyzer, or at least on a scope as you adjust the power and make sure you don't cause distortion issues by turning it too low. 73 ... Ron On Wed, Jun 21, 2023 at 6:21?AM Colin Kaminski <colinskaminski@...> wrote: I would run at 7 volts and cut the 12v trace to Q6. Then wire from the 12v line at JP27 to Q6 and insert a string of diodes to drop the voltage. This lowers the voltage to the finals. By adding more diodes you can drop the finals below the 7V requirement for the CPU voltage regulator. I marked the changes in yellow. (I haven¡¯t tried this¡.) |
EI7CLB
Ronald Taylor
Don VE3IDS
Don, ND6T
Bruce Akhurst
VE3KCL
Donald S Brant Jr