Date   

Re: 0.03w RF output, 1w at transistor drains, Help? #qcx

Arv Evans <arvid.evans@...>
 

#Measurements using an Arduino ADC

 Measuring of circuits requires knowledge of what you are 
measuring, and what you want to see.  For HF AC voltages 
you need either an oscilloscope of a detector type probe 
and a DC meter.  For measuring DC without seeing the AC 
you need a DC meter with a DC isolation probe that blocks AC.
For measuring HF AC you need an RFC probe that blocks 
and filters off the AC component.  All of these can theoretically 
be done using the ADC input on an Arduino, but each type of 
probe will need to be calibrated, or at least its offset from reality 
will need to be known and taken into account.  Input impedance 
of an Arduino ADC is usually around 500K ohms, but it does 
vary with frequency of input (HF, versus VHF, versus LF, versus 
audio.  This can be part of the probe calibration for each type of 
measurement.

Just using a simple Arduino ADC input, as is done in the QCX, 
provides a simple voltage tracing capability and a guess at the 
actual voltage level.  Some ADC circuits require settling time.  
For this reason it is best to allow time for at minimum 2 samples
with the 2nd sample being the most reliable.  Adding additional 
capacitance at the ADC input can help with accuracy, but at the 
expense of requiring more time to settle.  

If using the ADC of an Arduino for measurements you will need 
to be aware that it only measures positive voltages and is always 
referenced to the Arduino ground.  You cannot directly measure 
negative voltages and you cannot offset the ground reference.

There are ways to use an FET input type of op-amp prior to the 
ADC input to obtain higher input impedance and to offset the 
ground reference.  

You can use an antenna-side RF probe in Stockton-bridge format 
to measure FWD and REF power, but FWD and REF will need to 
be calibrated for accuracy.  You can use a summing type RF bridge 
to measure actual power between rig output and the antenna feed 
line, but this also requires calibration and impedances should be 
close to 50 ohms.  You can also use a bridge type comparator to 
measure actual HF impedance.  

Using a simple diode detector probe to measure the voltage 
at the rig output and feedline input will show relative power, 
but unless you can insure that the impedance at that point is 
exactly 50 ohms this reading is just relative to the reading you 
took an hour ago or yesterday.  It does not show true power 
levels.

All this is not to say that the ADC input of an Arduino, or any 
other microcontroller with ADC input, is not useful...just that 
you need to know what you are doing and how to do it before 
quoting it as an accurate measurement.  

Arv
_._



On Wed, Aug 19, 2020 at 11:24 AM spam via groups.io <spam=craftxbox.com@groups.io> wrote:
I dont know if there is RF , but I'm reading 11.97v (external meter) at the non-lpf side of c29, then 7v on the other side. Interestingly, there always seems to be ~4.7v at the rf output, unless its switched off? Replicated the same behavior of c29 with the other 104 cap, "5.2 watts" in, and practically nothing out


Re: 0.03w RF output, 1w at transistor drains, Help? #qcx

 

As far as i can tell, q1-3 are outputting , I dont have an oscilloscope to see what they're outputting, but that they ARE outputting something.


Re: U3S + for sale

Podolsky A <w8du@...>
 

This has been sold. Tnx fer looking.
73 de Arnie W8DU


Re: QRP-Labs 50 W Amplifier - low power output

ajparent1/KB1GMX <kb1gmx@...>
 

On Wed, Aug 19, 2020 at 10:46 AM, Ben Bangerter, K0IKR wrote:
I set the bias for 113 mA wit
Why?   The amp is class C so the bias should be what ever the board
draws and no more.

The adjustment procedure has the bias at zero and no signal in (CW practice mode)
and the bias is turn up until the board current inreases then backed off to the point
before that.

the waveforms are seriously distorted.  Maybe input transformer miswired or 
soldered.  you could have an  inter-turn short.

Something is wrong and its likely in the input side.

Allison

-------------------------------
Please reply on list so we can share.
No private email, it goes to a bit bucket due address harvesting


Re: Power rating for LPF Kit? #lpf

Dave VE3GSO
 

Bigger wire is less resistive, both in DC terms and also effective RF resistance.

A lower RF effective resistance increases the Q of the coil and decreases power loss. I try to wind most of my toroids with the largest gauge wire that will fit on the coil in a single layer.

If you are going to 630m that means a lot of turns, likely overlapping, so you will want to use a finer wire.  Likely the loss of Q will be a minor factor.

Using a bigger wire, while giving a higher Q, might get pretty difficult to fit the number of turns on the core, particularly if it is a FT37-2 core.  You may need to bump up to a FT50-2 or even larger!

Dave


On Aug 19, 2020, at 14:58, John AK4AT <john@...> wrote:

Related to this topic, is it correct to assume that using a larger diameter wire will not change anything as long as the same number of turns are used? I need to rewind one on a U3S for the 630m band and have slightly heavier wire on hand.

John


Re: Power rating for LPF Kit? #lpf

John AK4AT
 

Related to this topic, is it correct to assume that using a larger diameter wire will not change anything as long as the same number of turns are used? I need to rewind one on a U3S for the 630m band and have slightly heavier wire on hand.

John


Re: 0.03w RF output, 1w at transistor drains, Help? #qcx

Alan G4ZFQ
 

There does appear to be a path to ground through the LPF, however, It's not a dead short,
If you have a dummy load connected, as you should, then you will see 50 ohms.
The 104 capacitor check makes Q1-3 failure likely.

73 Alan G4ZFQ


Re: 0.03w RF output, 1w at transistor drains, Help? #qcx

Dave VE3GSO
 

There should be no DC path to ground in the low pass filter, as the RF caps should be many megohms to DC.

In vacuum tube output circuits, particularly PI tank circuits, an RF choke was always included near the low impedance output to allow a blocking capacitor charge path, else the power supply voltage would appear through the DC blocking cap on the PI network components and output. If a DC grounded antenna was connected then the DC blocking capacitor could charge when the RF amplifier was turned on, but if the antenna didn’t allow that current flow, then a dangerous shock hazard existed.

We don’t usually worry about such things now, with 12 volt or 20 volt supplies, but if you do probe the output with a high impedance meter and don’t have a DC path load connected to the output of the low pass filter, like a 50 ohm dummy load, you will see the supply potential until the current through the meter has allowed the DC blocking cap to charge.

Dave


On Aug 19, 2020, at 13:33, spam via groups.io <spam@...> wrote:

There does appear to be a path to ground through the LPF, however, It's not a dead short, and appears to be through a capacitor, which is to be expected?
C29 appears to be working fine as far as i can tell.


QRP-Labs 50 W Amplifier - low power output

Ben Bangerter, K0IKR
 

I constructed my 50 W amplifier For 20 M at the end of June, and the assembly process went well.  I set the bias for 113 mA with A 20.1 V power supply, no RF power input, and both the input and output ports terminated in 50 ohms.  I tested the amplifier briefly driven with my original QCX, which puts out 2.0 W with a 12 V supply.  My Bird power meter with a 50 W slug Indicated ~15 W to a dummy load.  I then set the amplifier aside while I awaited my QCX+.  That was assembled and aligned, and it delivers ~2.5 W (32 V p-p on the scope) to a 50 ohm dummy load.  When the amplifier, supplied with 20.1 V, is driven by the QCX+, it only delivers ~12.5 W (71 V p-p) To a dummy load.  This is not highly dependent on the amplifier bias setting (3.1 V in this case for the standing current threshold), nor on the power from the QCX+, which can be adjusted by adjusting its supply voltage over a 10 - 14 V range.  I looked at rf waveforms at various places in the amplifier circuit.  Here are waveforms at the gates of the IRF510s, Q1 in yellow and Q2 in violet:

 The drive signals differ in phase by ~180 degrees as expected for a push-pull circuit, but the Q1 waveform in particular appears highly distorted.  The waveforms do not change much at higher bias settings.  This is the waveform at the drain of Q1; that for Q2 is nearly identical.

The frequency of this waveform is ~42 MHz, indicating high third harmonic content.  The amplitude between the cursors is 103 V p-p.  The next waveform is at the secondary of the output transformer at the input to the low-pass filter:

The shape of the waveform is the same as that at the Q1and Q2 drains, the p-p voltage here is 246 V.  The output of the amplifier, after the low-pass filter, is a nice sinusoid at 14 MHz, as expected, but just 92 V p-p, and which dropped to 71 V p-p over time as testing continued.  At no point during my testing did the heat sink become the slightest bit warm to the touch.  The final photo shows the voltage at the input to the low-pass filter with markers to indicate the time interval between the indicated peaks, here 71.6 nS, corresponding to 14 MHz.



i checked the amplifier over carefully, and all the components appeared to be the right values in the right places.  I thought the output transformer might have been reversed.  I removed it and unwound it, and found it was installed correctly.  Then I rebuilt it with new wire and reinstalled it.  While it was out, I examined the low-pass filter with my spectrum analyzer/tracking generator, and saw it had a 3 dB cut-off frequency of ~ 16 MHz, and a loss at 14 MHz of 0.25 dB.  I thought the problem might lie in the T/R switching circuitry, as an incorrectly installed or bad diode could clip the rf waveform and create harmonics.  Checking in both T and R modes, the four 1N4007 diodes all had the correct forward bias currents and correct reverse bias voltages, depending on the on/off condition.  These were examined with amp bias set to zero and no rf input or output.  The rf voltage doubler circuit produced 186 volts when the amplifier was delivering its (measley) 14 watts or so to the dummy load.

At this point, I have run out of ideas, other than replacing the two power MOSFETs.  I have been reluctant to do that except in desperation, being concerned about damaging the pcb.  If anyone has any suggestions for resolving this problem, I will be overjoyed to hear them,

73, Ben K0IKR



Re: 0.03w RF output, 1w at transistor drains, Help? #qcx

 

There does appear to be a path to ground through the LPF, however, It's not a dead short, and appears to be through a capacitor, which is to be expected?
C29 appears to be working fine as far as i can tell.


Re: 0.03w RF output, 1w at transistor drains, Help? #qcx

 

I dont know if there is RF , but I'm reading 11.97v (external meter) at the non-lpf side of c29, then 7v on the other side. Interestingly, there always seems to be ~4.7v at the rf output, unless its switched off? Replicated the same behavior of c29 with the other 104 cap, "5.2 watts" in, and practically nothing out


Re: Power rating for LPF Kit? #lpf

Carl-N6TVN
 

Hi, QCZ+ 700 hz tone in BPF peak is very weak, also IO screen is jumping? Checked toroid connections and resoldered.


Re: Power rating for LPF Kit? #lpf

ajparent1/KB1GMX <kb1gmx@...>
 

First limiting factor is caps with 50V rating.  That can tolerate 20W but only if
the SWR is under 2:1.  Bump up to 100V parts and you in the comfortable
25-30W level. More than that 200V or higher.  As you go higher in power
the voltage is only part of the issue as then currents (though caps) increase.

The cores and wires are less a limit and they can get to 30W or more though
I'd stay under 50W with T37 sizes and 70W with T50 size.  For 100W use
T68 size for reasonable margins.  Wire,  #28 is generally enough but 26 and
24 as power goes up.  You need larger cores to fit larger wire.

Experience is that to 10W life is easy and simple, getting to 50W justifies
the effort to go 100W.  Why?  every thing has to be bigger, heavier, and 
higher voltages and currents.

Allison
-------------------------------
Please reply on list so we can share.
No private email, it goes to a bit bucket due address harvesting


Re: 0.03w RF output, 1w at transistor drains, Help? #qcx

Shirley Dulcey KE1L
 

Thank you for this answer, W4JED. That's a point that a lot of us missed; we were assuming there is actually RF on the non-LPF side of C29. The suggestions people (including me!) have been making about C29 open or shorted capacitors in the LPF are correct if there is RF (which you can verify with an oscilloscope or an RF probe), but if there is little or no RF present you need to look elsewhere for the solution.


On Wed, Aug 19, 2020 at 8:50 AM James Daldry W4JED <jim@...> wrote:

PUH-LEEZE!!

When applied to a point with a DC voltage, the "wattmeter" reads the DC as "watts". Any DC voltage above a certain level (Hans could probably tell you what that level is) is read as 5.2 "watts". Meaning, any "watt" readings on the drains of Q1,2,3 are meaningless. It only tells you that the DC is getting there. If you were to touch the 12 volt input connection it would read 5.2 "watts". Look at the schematic. There is no blocking capacitor to keep the DC out of the A to D converter. Before C29, MEANINGLESS. After C29, sorta OK. At the antenna jack (where there is an actual sine wave) something like an actual reading, provided it is connected to a 50 ohm dummy load. Not an antenna, because the impedance of an antenna can be all over the place, and the reading will change with impedance.

73

Jim W4JED

On 8/18/20 8:57 PM, spam via groups.io wrote:
I'm measuring '5.2w' on the input of c29, and only 0.14w on the other side, I'm assuming this is not correct here


U3S + for sale

Podolsky A <w8du@...>
 

Mates:
I have the following for sale. 99 percent assembled but never powered up or aligned. Just don't have time for it. SO here is what I have:
U3s - Rev 3 F/W 3.12
GPS QLG1
Relay LPF board
LPF for 40, 30 20 meters (40 meter board not assembled)

Price is $50 plus actual shipping (USA sales only, no shipping outside USA)
Please send me an EMAIL to mycall at arrl d ot ne t if you want it.
Tnx de Arnie W8DU


Re: 0.03w RF output, 1w at transistor drains, Help

Jim Painter
 

Jim, good information. Thanks...

Jim...kq3s


On Wed, Aug 19, 2020 at 8:50 AM, James Daldry W4JED
<jim@...> wrote:

PUH-LEEZE!!

When applied to a point with a DC voltage, the "wattmeter" reads the DC as "watts". Any DC voltage above a certain level (Hans could probably tell you what that level is) is read as 5.2 "watts". Meaning, any "watt" readings on the drains of Q1,2,3 are meaningless. It only tells you that the DC is getting there. If you were to touch the 12 volt input connection it would read 5.2 "watts". Look at the schematic. There is no blocking capacitor to keep the DC out of the A to D converter. Before C29, MEANINGLESS. After C29, sorta OK. At the antenna jack (where there is an actual sine wave) something like an actual reading, provided it is connected to a 50 ohm dummy load. Not an antenna, because the impedance of an antenna can be all over the place, and the reading will change with impedance.

73

Jim W4JED

On 8/18/20 8:57 PM, spam via groups.io wrote:
I'm measuring '5.2w' on the input of c29, and only 0.14w on the other side, I'm assuming this is not correct here


Re: One more problem U3S WSPR

Vernon Matheson
 

You should read again John...copied and pasted from the assembly instructions.

Cheers

Vernon

On 2020-08-19 14:31, John McClun wrote:
From what I read in my build instructions, position 0 must have the highest band module.  In my case 10M (28Mhz).


Re: One more problem U3S WSPR

Roger Hill
 

Hi John:

No that is wrong.

Highest band goes in position 1. Read the manual carefully.

Regards

Roger

G3YTN

---
***************************
Roger Hill
***************************


On 2020-08-19 15:31, John McClun wrote:

From what I read in my build instructions, position 0 must have the highest band module.  In my case 10M (28Mhz).


Re: One more problem U3S WSPR

John McClun
 

From what I read in my build instructions, position 0 must have the highest band module.  In my case 10M (28Mhz).


Re: Alignment process

Brent DeWitt
 

I agree with Curt that the built-in bar graph works very well, but the auto-scaling can be a bit distracting.  as an alternative, I've found that simply listening with a decent pair of headphones allows me to null the adjustments pretty well.
-- 
73,
Brent DeWitt, AB1LF
Milford, MA