if (d--==r) lcd.print('.');

What??

Jack, W8TEE


On Sunday, May 6, 2018, 10:41:34 AM EDT, Jerry Gaffke via Groups.Io
<jgaffke@...> wrote:


Here's my unproven code for displaying forward and reverse power in Watts
plus SWR on the bottom line of the 16x2 LCD, when using a TandemMatch
with diode detectors.
It's actually quite simple and not computationally expensive.. Hereby
released under GPL v3.0

Could be made more accurate by adding the schottky diode drop to the two
voltage readings.
Assuming the transformer turns ratios are kept at 10:1, the SWR should
be reasonably accurate
without calibration. Especially if a few uA of bias is added to the diodes.
Power readings should be reasonably accurate if the SWR is close to 1:1
since they assume a 50 ohm load.

Maximum analogRead() return value is 1023, and represents a peak RF
voltage of 5 volts.
Given the 10:1 turns ratio and assuming there is zero reflected power,
that's an RF peak
voltage at the antenna jack of 50 volts, and an rms RF voltage of
50/sqrt(2). Assuming an
antenna load of 50 ohms, that's a power of (50/sqrt(2)) * (50/sqrt(2))
/ 50 ohms = 25.0 watts.
From this, we determine the value of PSCALE in the code below.

Using the linear-in-db ad8307 could be done with the same code, but
first using
a table lookup to convert to RF volts.
I don't really want to be computing anti-logs on a Nano.
A table lookup will burn some flash.

################################################################
// Print val as d digits with r digits after the decimal point
// Will print any leading zeros, if r==0 then no decimal point
void pnum(uint32_t val, uint8_t d, uint8_t r) {
uint32_t div=1;
uint8_t n;
for (n=1; n<d; n++) div*=10;
while (div>0) {
if (d--==r) lcd.print('.');
lcd.print((val/div) + 0x30);
val = val%div;
div = div/10;
}
}

// Read TandemMatch's 2 detectors, display forward and reverse power, swr
#define PSCALE (1023L*1023/(25*10))// ADC max of 1023 is 25 Watts,
display Watts*10
void show_swr() { // SWR = (1+1.0*vr/vf)/(1-1.0*vr/vf);
uint32_t vr, vf, swr;// Voltage squared proportional to power
vf = analogRead(RF_FWD);// Peak RF volts from forward detector
vr = analogRead(RF_REV);// Peak RF volts from reverse detector
if (vr>=vf) swr=0; // If vr,vf illegal, force SWR to zero
else {
swr = (vr*1024)/vf;// Voltage ratio, 10 fractional bits
swr = (1000*(1024+swr))/(1024-swr);// 1000*swr, nearly 10 fractional
bits
swr = (swr+50)/100;// 10*swr, rounded to nearest tenth
if (swr>99) swr=99; // Display a max SWR of 9.9
}
lcd.setCursor(0, 1);// Fill bottom LCD line, example:
lcd.print('f'); pnum(vf*vf/PSCALE,3,1);// "f12.4 r03.1 s1.7"
lcd.print('r'); pnum(vr*vf/PSCALE,3,1);// with fwd,rev power in watts
lcd.print('s'); pnum(swr,2,1);// and swr to max of 9.9
}
#################################################################

My primary reason not to mess with ad8307's is that they are harder to
dead bug.
If the timing skew between forward/reverse readings is an issue, I'd
definitely try the cap.
Likely still accurate enough.

Bill wrote:

58.6 KHz would be ok, but to get that rate probably assumes that the

processor is dedicated to the task, not off doing other uBITx work,


We currently use a blocking analogRead() in many places in the code,
each taking over 100us.
And in some cases do it constantly for stuff such as inspecting switches
or keyer paddles.
So speeding up the analogRead() by a factor of 5 and occasionally (once
per second?)
reading the forward and reverse power should not be much of a burden,
even if averaging
a half dozen reads.

Should be possible to set up the ADC to be interrupt driven, an
interrupt service
routine updates a list of all ADC readings. In mainline code, we'd then
disable interrupts
and read those last few forward and reverse readings to take an
average. Since we
are no longer blocking for each 100us+ analogRead(), this would be much
less a timing burden.

Things may eventually slow down too much for somebody trying to use the
keyer at 40wpm.
Otherwise I doubt there will be much of an issue with a lost millisecond
here and there.
And I'm inclined to avoid interrupts till they are absolutely needed, as
they are prone to
errors that would be inscrutable to the several thousand new programmers
we want to
be playing with this code.

Jerry, KE7ER


On Sat, May 5, 2018 at 10:45 pm, K9HZ wrote:

Hmmm… we should probably take this off-line at this point. This has
to do with A/D resolution time vs. filter time.

I’m rethinking…that diodes would be a better choice just because
they are less complicated. The transform to watts and SWR is still
complex though and will eat some processing power in a Nano.

Gee, isn't this about the 8th different topic posted under the same
subject line?

Rod KM6SN

?

Slowing down processing by additional code. Yes I'm extremely aware of this problem hence the my posts on timing. An outboard I2C A/D removes a lot of this load because 1) we are already using the I2C library for other functions in the radio, and 2) the update frequency requirements once off the original Arduino are much lower.

if (d--==r)? ?lcd.print('.');

What??

Jack, W8TEE

?

My problem is that my tuner, a homebrew z-match type, doesn't have an
swr meter. When operating portable, with a compromise antenna, knowing
the swr doesn't matter much unless you have that "extra" box normally
called a tuner. 

I'm just saying that knowing the swr doesn't matter much to me,
especially if it takes up more precious nano resources. All I need is a
reverse power indicator to tell when the tuner has matched the antenna.
The output power is going to be whatever it will be, there isn't much
you can do about it in the field. You don't normally adjust a tuner for
maximum output, you adjust it for minimum reflected power. 

Any random piece of wire is going to work as an antenna. The issue is
whether you can match the rig to the antenna using a tuner. 

tim ab0wr



On Sun, 06 May 2018 07:57:01 -0700
"Jerry Gaffke via Groups.Io" <jgaffke@...> wrote:

The goal is whatever we want it to be.

Showing SWR on the uBitx makes it useful for verifying an antenna
system is working without having to lug about an extra box,
especially when operating portable. If it costs an extra $3 in parts,
I'm fine with adding it to the rig.?

If you have a tuner that already shows SWR and forward power,
and your antenna needs a tuner anyway,
then your goal may be different.

Jerry, KE7ER

On Sun, May 6, 2018 at 07:43 am, Tim Gorman wrote:

Jerry,

What is the goal here? Is a wattmeter function really needed inside
the ubitx? Or would it be better as an external attachment that can
be used with other equipment?

For me, measurement of the reverse power is the primary measurement
needed inside the ubitx. It is useful for adjusting an external
tuner and for deciding if the ubitx is at risk from a bad load. I
am using the simple circuit at the nd6t site to get the reverse
power measurement. Right now I am using an external analog meter
but I have an adafruit ADS1015 that I am going to use when I get my
ubitx working again. I am using a little 4x4 breadboard to make an
I2C bus expander and the ADS1015 will feed into this along with the
I2C lcd.

Coding for this is extremely simple. You don't even have to convert
to volts. Just display the reading from the ads1015. As it goes
down you know the reverse power is going down. If you want to do it
with an analog pin on the nano you can do that too.

Just my 2cents. FWIW.  

Jerry,

I tried raising the voltage on my final to 24v. It didn't help the 3rd
order IMD at all. I suspect most of the IMD is coming from crossover
distortion, not flat-topping.

tim ab0wr

On Sat, 05 May 2018 21:44:28 -0700
"Jerry Gaffke via Groups.Io" <jgaffke@...> wrote:

Very cool, thanks for digging into this.
I tried various schemes in LT-Spice, but improving the final is more
difficult than it seems going in.?
I could seldom correctly predict the results I got.
Need to re-read a few chapters of EMRFD.?
And of course, real hardware is likely quite different than the
simulation.

So is this still the previously reported? 4W at 30m, 13W on 80m?

Would raising the PA-PWR voltage to 24v improve that IMDR?
Perhaps if keeping power down to something reasonable with RV1,
we could get by without up-sizing the heatsinks.

Jerry

On Sat, May 5, 2018 at 09:28 pm, Ashhar Farhan wrote:

So, here are the final mods,?
Replace C81 from 0.1uf to 470pf
Replace R83 from 10 ohms to 2.2 ohm
(you can short R83 as well)?
Replace 97, R98 from 47 ohms to 220 ohms
Remove C261, C262.?
?
So, what happens is that removing the C261 and C262 increases the
gain of the finals. They are run open. Hence greater gain at 28
mhz. However, the gain is very high at lower frequencies. So, in
order to reduce the gain at the lower frequencies, the 0.1 uf cap
is replaced by the 470 pf. As the frequency of the signal drops,
less and less RF flows through the 470 pf, decreasing the gain of
the predriver. 470 pf is not a magical value, 220 pf works almost
as well. Here are the pictures at 14 mhz. The two tone test reveals
20 db IMDR, which is alright. If you want to see better, buy
yourself two RD16HHF1s.
- f

Hmmm… we should probably take this off-line at this point.? This has to do with A/D resolution time vs. filter time.

I’m rethinking…that diodes would be a better choice just because they are less complicated.? The transform to watts and SWR is still complex though and will eat some processing power in a Nano.

Jerry,

What is the goal here? Is a wattmeter function really needed inside the
ubitx? Or would it be better as an external attachment that can be used
with other equipment?

For me, measurement of the reverse power is the primary measurement
needed inside the ubitx. It is useful for adjusting an external tuner
and for deciding if the ubitx is at risk from a bad load. I am using
the simple circuit at the nd6t site to get the reverse power
measurement. Right now I am using an external analog meter but I have
an adafruit ADS1015 that I am going to use when I get my ubitx working
again. I am using a little 4x4 breadboard to make an I2C bus expander
and the ADS1015 will feed into this along with the I2C lcd.

Coding for this is extremely simple. You don't even have to convert to
volts. Just display the reading from the ads1015. As it goes down you
know the reverse power is going down. If you want to do it with an
analog pin on the nano you can do that too.

Just my 2cents. FWIW.

On Sat, 05 May 2018 15:52:36 -0700
"Jerry Gaffke via Groups.Io" <jgaffke@...> wrote:

Kees,

Consensus on the EMRFD yahoo group was that the ebay AD8307's worked
fine:

Some posts there are guessing that when boards get autostuffed from
reels there are often a few parts remaining at the end of the reel,
and the ebay sellers make the remnants available cheaply. Though if
that were truly the case, I'd expect more parts to get sold at 95% off
list price like that.

Diz already has a Stockton/TandemMatch kit at what I think is a
reasonable $12 plus shipping:
Shipping probably has to be
more than $0.70 because of the toroids. Uses 1n5711 schottky diode
detectors.

I mentioned here that I was planning to substitute a couple AD8307's
but Arv convinced me to first try biasing the 1n5711's to make them
more sensitive. /g/BITX20/message/47628
You probably already saw that, it's in this same thread.

I wrote Nano code for the Tandem Match to display forward and reverse
power in Watts, also SWR. but it's also a major rewrite of all the
uBitx code and I got lost in the weeds fiddling with other stuff for a
few weeks. I'll try to get my code going in the next few days. The
AD8307's would give more dynamic range, but I think the 1n5711's with
bias will be plenty polite. Displaying Watts and SWR from the AD8307's
linear-in-dB output would be slightly more difficult on our
computationally challenged Nano. I'm planning to use A6 and A7 for
the bridge, move the paddle to digital pins D0 and
D1 (which are currently unused except when downloading firmware).

Anybody worried about smoking their expensive RD16HHF1 FET's could use
the reflected power reading to shut down the transmitter when
their EFHW antenna falls to the ground in the wind. ;-)

Jerry, KE7ER

On Sat, May 5, 2018 at 01:30 pm, Kees T wrote:

I just uploaded the current AGC and Click kit requests. This list
is to help me asses demand so I can have the correct sets of parts
ready. There does not appear to be much demand for boards only,
just complete kits.

I'll post prices later, when I receive the boards and some testing
is done.

I was looking into Don's ND6T Polite Antenna Tuner, but there does
not appear to be much interest and using it effectively may be a
problem, so it's out. I did receive a request for a "Power Level
Upgrade" kit but decided against that because there is a whole lot
of testing to be done when you get into RF Amplification.

What may make sense, unless it's already out there as an add-on
upgrade kit, is a Power/SWR capability using a simple Stockton
Bridge and a couple of AD8307's. I'm quite familiar with the bridge
and the AD8307 parts are getting really cheap <$0.50 each. Wonder
if those Chinese parts are usable at QRP specs ? Would need two
analog inputs on whatever microcontroller .......and, of course,
the ever present requirement for *someone* to provide support
firmware.

73 Kees K5BCQ