Re: ND6T AGC implementation for uBIT-X
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Bill K9Hz
I am impressed by your ATU design.? That should be of interest to the BITX group when you
publish it.? Will you be manufacturing and selling the unit as an on-line product??
From wondering if there might be a QRO version of your ATU I took a look at your "The QRO Group"
< /g/QRO>? and found that there are only 6 members, and that there have been only 6 posts from 2017 until now.? All of those posts seem to be from you.? Does that mean that QRO may be a dying mode...? ?? ? A slightly off-topic question, what discipline is your doctorate in?? Is it based on a PhD, or some other
type of "doctor"?
Arv
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On Sat, May 5, 2018 at 11:45 PM, K9HZ <bill@...> wrote: ´¡°ù±¹¡ ? 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. ? My tuner is prototyped and the hardware is done.? The firmware is in the writing stage¡ I¡¯m waiting for Jack to finish his Jackal project and a another second follow-up project before I officially ask for his help in coding.? It can tune 100 watts from any source (meaning it can be stand-alone¡ or I2C linked to the uBITx), uses latching relays to conserve power for QRP, has a 1:4 transformer for very low loads like the illusive short length impedances at very low frequency (12 ohms), CL-LC swap for high-low impedance matches of us to almost 12,000 ohms, ?an AD8302 to generate phase and magnitude information of the load impedance like a point on a smith chart and then calculates the LC transform directly and instantly¡ no clicking-clacking relays searching for lowest SWR.? SWR and power is calculated and can be retrieved over the I2C or analog via the onboard dedicated Arduino (for those interested, the LP-100A watt meter generates power and SWR readings this way).? There is also a low power tune mode Dig Out to save the relays and protect the transmitter by commanding lower power (works down to about 250 mW).? So far it fits on a 5¡±x3¡± board but I may be able to shrink it.? Stay tuned. ? ? Dr. William J. Schmidt - K9HZ J68HZ 8P6HK ZF2HZ PJ4/K9HZ VP5/K9HZ PJ2/K9HZ ? Owner - Operator Big Signal Ranch ¨C K9ZC Staunton, Illinois ? Owner ¨C Operator Villa Grand Piton ¨C J68HZ Soufriere, St. Lucia W.I. Rent it: Like us on Facebook! ? Moderator ¨C North American QRO Group at Groups.IO. ? email:? bill@... ? ? From: [email protected] [mailto:[email protected]] On Behalf Of Arv Evans
Sent: Sunday, May 6, 2018 12:05 AM
To: [email protected]
Subject: Re: [BITX20] ND6T AGC implementation for uBIT-X ? Not sure I follow your analysis.? The added capacitance lowers upper frequency limit by a significant amount. You can even go as high as 0.1 MFD so that the detector output is filtered to virtually DC, leaving no HF knee in the passband.? This does cause a charge period error unless there are multiple samples to charge
this capacitor.? Same thing applies to simple diode detection with it's post-detection filter capacitor.? The Arduino ADC provides 1023 distinct voltage steps.? It's internal voltage reference is used for calibration. With a maximum of 5V and 1023 steps this gives a minimum sensitivity of around 0.005V and 5V full scale. That range and resolution seems adequate for most transmitter RF measurements. It may be interesting to try using conventional diode detection with a small forward bias to overcome the diode offset.? This is not usually done in conventional SWR bridges because they are mostly non-powered units.? But if the SWR bridge is to be inside a powered transceiver then the bias is readily available. Now that AD8307 prices are more reasonable this device may be a viable alternative detector but it's log slope ADC requires a bit more complex software if you want to derive the full compliment of FWD and REV power, FWD and REV SWR, RF Voltage, RF Current, and possibly RF Impedance.? With either diode or AD8307 detectors it should be relatively easy to make the software support automatic calibration.? Possibly this could be based on measurement of the known output of one of the Si5351a ports. Using and displaying this output could also be a test point to verify that the synthesizer chip is actually operating at normal levels. Some time ago you mentioned work on a QRP ATU of your own design for use with BITX transceivers.? How
is that coming along?? Are you planning on including SWR and power measurement capability at both input and antenna ends of this unit?? Might be interesting to include calculation and display of impedance, particularly at the transmitter end of the ATU to help get a good 50 ohm match to the IRF510 finals and associated LPF. As you know, impedance is important when using an LPF designed for a specific cut-off frequency in order to
make the LPF operate within its design parameters. ? On Sat, May 5, 2018 at 7:26 PM, K9HZ <bill@...> wrote: ´¡°ù±¹¡ ? I¡¯m quite familiar with the 8307 characteristics¡ there is a an effective 12.5K on chip resistor that forms part of a low-pass filter in shunt form basis that external capacitor.? It¡¯s designed to reduce the ripple of the output and as I recall has a corner frequency of about 5MHz with the suggested capacitor (10 or 100nF from memory).? As you change the corner is also loads the output and changes the slope factor.? Not a big deal but you need to recalibrate.? It being faster than an analog meter is not really relevant and actually part of the problem.? What is relevant though, and what you see in the lab is that the P-forward resolved by the Nano A/D pin ¡°x¡± finishes at ¡°t¡± and P-reverse is resolved by Nano A/D pin ¡°y¡± at ¡°t+n¡± where ¡°n¡± is what makes the difference.? Because of that filter above, it¡¯s frequency dependent.? Most folks just calculate away for SWR and get a number and figure its right.? Might be.? Might not.? Someone actually wrote an article for QST on this. ? Anyway¡ I tried. ? ? Dr. William J. Schmidt - K9HZ J68HZ 8P6HK ZF2HZ PJ4/K9HZ VP5/K9HZ PJ2/K9HZ ? Owner - Operator Big Signal Ranch ¨C K9ZC Staunton, Illinois ? Owner ¨C Operator Villa Grand Piton ¨C J68HZ Soufriere, St. Lucia W.I. Rent it: Like us on Facebook! ? Moderator ¨C North American QRO Group at Groups.IO. ? email:? bill@... ? ? From: [email protected] [mailto:[email protected]] On Behalf Of Arv Evans
Sent: Saturday, May 5, 2018 7:48 PM
To: [email protected]
Subject: Re: [BITX20] ND6T AGC implementation for uBIT-X ? Bill K9Hz
Adding a small external capacitor (o.001 mfd) at the input of each ADC provides extra stabilization versus time for the voltage samples.? This added capacitance can be thought of as part of the
detector filter. ? The sample rate of an AVR Mega-328 is quite fast but this adds a bit more pre-hold
or averaging to the traditional sample-and-hold function.?
I would not worry about time shifting of ADC measurements because it is still faster than a ballistic
meter movement that we have all relied on for many years.? If you really want traditional mechanical
meter results you can slow down the sample rate or average several samples to arrive at an? averaged voltage reading. In addition to measuring forward power, reverse power, and RF voltage, you can measure RF current by using a current-transformer (like those in the Stockton or Bruene bridge) to get a voltage reading that translates from RF current.? This may be very interesting for those who are using a uBITX or QCX transceivers for VLF.??? <> ? On Sat, May 5, 2018 at 6:23 PM, K9HZ <bill@...> wrote: The I2C isn¡¯t all that important.? What is important is the sample and hold.? Otherwise your forward and reflected power signals can be time shifted and won¡¯t make sense.? But maybe again, if accuracy isn¡¯t important to you, this isn¡¯t either.? Ten turns of any small transformer wire on the T50-43 or smaller core works perfect. ? ? Dr. William J. Schmidt - K9HZ J68HZ 8P6HK ZF2HZ PJ4/K9HZ VP5/K9HZ PJ2/K9HZ ? Owner - Operator Big Signal Ranch ¨C K9ZC Staunton, Illinois ? Owner ¨C Operator Villa Grand Piton ¨C J68HZ Soufriere, St. Lucia W.I. Rent it: Like us on Facebook! ? Moderator ¨C North American QRO Group at Groups.IO. ? email:? bill@... ? ? From: [email protected] [mailto:[email protected]] On Behalf Of Kees T
Sent: Saturday, May 5, 2018 6:59 PM
To: [email protected]
Subject: Re: [BITX20] ND6T AGC implementation for uBIT-X ? The eBay sellers (many) are providing boards with AD8307s on them and also strips of AD8307 parts. On my mWattmeter II kit I provided a "matched set" of HP diodes which were forward biased with a few uA (AAA cell) to allow readings <1mW.....and it worked very well as measured in a local professional lab. I don't think that accuracy is required here. I can provide an I2C interface as Bill, K9CZ, suggested but don't know if that's really required here either.
I later gave the mWattmeter II design to Ron, W4MMP, for production because I got tired of making mWattmeter II kits.?
I realize Diz makes a coupler but this one would be smaller? ...maybe 1" x 1-1/2" and use the dual double #61 FT-37 size toroids with Faraday shield and 23 turns, which I found to work best. A LOT of coffee cup coasters were made during that time. I have an old schematic but it's in .bmp format and won't load into the Files section.??
73 Kees K5BCQ??
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