On Sun, Aug 11, 2019 at 02:39 AM, Robert McClements wrote:

Review video not up to usual ARRL standards - could have done better.

Glad to see more coverage for the ?BITX but the video showing an aftermarket enclosure as if it is standard is only going to create confusion.
?
--

Definitely by the time I got my novice (late 70s) VFOs were allowed; I quickly came to appreciate the value of that VFO.

MVS Sarma
Definitely the LM317 is more power hungry. Have a good sized heat sink on it. It has to adsorb 5 volts at maybe 150-200 milliV But a linear is quiet and I thought that the having the receive quiet was worth it. Not measured however. The computer power supply is linear I am pretty sure.

I was not sure whether to change the settings the bias so I left it alone. The uBITX puts out more than 20w on 40 and higher on 80 which I hardly ever use. It is a v3 radio.

It also has large computer heat sinks At least 4x heavier than the stock heat sinks. a 80mm low speed fan and a printed shroud. The output transistors don't go above ambient in digital mode at 20 watts with 1:1 SWR.

My technique is to touch the transistors. I figure the less heat the less degradation there will be.

Actually, the value of the pot is not that important and a 10K will work as well as a 100K. The pot is between 5v and ground and you are just adjusting the voltage when "tuning" and that doesn't depend on the pot value.

The "jumping" is part of the original design. Since the ability to tune (especially with a single turn pot) gets very hard with the small adjustment available, the program is design to start jumping at either end (voltage close to zero or 5v) to step to a new tuning range. There are some fixes for that if you don't like it. One is to add resistors and shorting push buttons so it never reaches the end of rotation range, but you can step up or down with the buttons. Another is to modify the code to change the range you want to tune and even eliminate the jumping. I suggest loading Allard Munter's sketch for the BitX40 as it allows you to easily change the range you are tuning from the menu and offers a better tuning resolution through the technique of quickly averaging a bunch of readings for more accuracy. It really makes a fine improvement on the BitX40 and his illustrated instructions for some simple hardware mods (not required) add even more flexibility.

=Vic=

Review video not up to usual ARRL standards - could have done better.

A couple weeks ago I released a fan shroud for the "tall" Sunil case. See?

Since then, I was curious on its effectiveness vs just heat sinks or heat sinks and a fan.? So here are the results....

Test Setup:
- ubitx v4 with stock PA transistors and the new larger heat sinks being shipped with the case.
- Noctua 1800RPM 80mm 12V fan (Blowing in)
- Little Volt/Temp guage that I mounted on my front panel (unfortunately, I accidentally purchased the fahrenheit version...) Search for: " DROK Car Voltage Temperature Display" on amazon.
- Unfortunately I took the "shroud measurements" on a different day than "no shroud". So focus on temp gain from "ambient" as a comparison
- First set of tests were 5 minutes @ 40m into a dummy load
- Second set was FT8 CQ into a dummy load until the watchdog timer terminated transmissions.




The Results....

No Shroud .? ? ? ? ? ? Ambient? ? ? ? ? ? ? ? ? After 5 Min Xmit? ? ? ? ? ? ?Temp Gain
Fan Off? ? ? ? ? ? ? ? ? ?81F? ? ? ? ? ? ? ? ? ? ? ? ? 128F? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?+47?
Fan On? ? ? ? ? ? ? ? ? ?76F? ? ? ? ? ? ? ? ? ? ? ? ? ?94F? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? +18

WITH Shroud .? ? ? ? Ambient? ? ? ? ? ? ? ? ? After 5 Min Xmit? ? ? ? ? ? ?Temp Gain
Fan Off? ? ? ? ? ? ? ? ? ?83F? ? ? ? ? ? ? ? ? ? ? ? ? 128F? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?+45
Fan On? ? ? ? ? ? ? ? ? ?81F? ? ? ? ? ? ? ? ? ? ? ? ? ?98F? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? +17? ? ?

It looks like 5 minutes into a dummy load implies that a Fan is probably as good as a Fan and a Shroud.?

However, I went on to measure FT8 CQ (into Dummy, until watchdog kicked me out)

WITH Shroud .? ? ? ? Ambient? ? ? ? ? ? ? ? ? After 5 Min Xmit? ? ? ? ? ? ?Temp Gain
Fan Off? ? ? ? ? ? ? ? ? ?84F? ? ? ? ? ? ? ? ? ? ? ? ? 105F? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?+21? ? ? ? ? ? ? ? ? ? ??
Fan On? ? ? ? ? ? ? ? ? ?82F? ? ? ? ? ? ? ? ? ? ? ? ? ?88F? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? +6? ?

Of course the missing measurement is the FT8 CQ with just a Fan. Thought of this test *after* I put everything back together. :-( .

Next time I tear things apart I will update with this missing result. Meanwhile, if anybody out there wants to run this test, I would sure be interested in the gain.

73
Mark
AJ6CU

On Sat, Aug 10, 2019 at 11:46 AM, Gordon Gibby wrote:

It’s a simple biasing circuit, if the collector voltage rises a bit then more base current will be injected to bring the collector voltage lower.

Gordon covered the Q70 biasing arrangement very well, too.

Tom, wb6b

So there is a early draft users guide in the folders section with the following calibration steps. There may be better instructions in some other guide.? I am way too lazy to do a complete search.?

User Manual for KD8CEC uBITX software rev 1.061
/g/BITX20/attachment/45949/0/ug-toc2-rev0.52.pdf

If someone wants to make a youtube vid of the calibration procedure for a newbie, I would venmo them $10, or make a contribution to the foundation of their choice.

Note:? I have not tried these steps. I don't know if they work.? They seem unbelievably easy and straightforward. Which is why I would never try them. I would surly cause a warp in space time fabric with these 5 steps.
==============================

The uBITX reference oscillator on-board can be accurately calibrated using this menu.

The procedure is: 1. put the ubitx in USB mode

2. connect an antenna to the uBITX to listen WWV; alternatively connect a calibrated signal source at 10 MHz to the antenna input?

3. navigate the menus to get to the Set Calibration entry, and press the Function Sw. The uBITX will tune to 10,000,000 Hz, but the display will not show that.

4. rotate the encoder until you hear the zero beat

5. Carefully push the Function SW to save the calibration As a result of this process, uBITX frequencies will be within a few Hz of the dial setting.

For those who have access to a high resolution frequency counter, as an alternative to the above, you can: connect the uBITX to the counter via a pad of at least 20 db, and hold the CW key down while adjusting the uBITX encoder until you see on the frequency is exact. Then carefully push the Function SW to save the calibration.

Set the BFO

Set the BFO frequency used in USB and LSB. Rotate the encoder to vary the BFO frequency, then press the mic PTT switch to confirm. If you do not want to change the BFO frequency, press the function switch to abort.

Set CW RX BFO

Set the BFO frequency used in USB and LSB. Rotate the encoder to vary the BFO frequency, then press the mic PTT switch to confirm. If you do not want to change the BFO frequency, press the function switch to abort.

Change CW Tone

Set the CW sidetone frequency. Rotate the encoder to vary the CW sidetone frequency, then press the mic PTT switch to confirm. If you do not want to change the BFO frequency, press the function switch to abort

etc. etc. etc.

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The fact that you have to turn into a higher frequency indicates the internals of the microbitX may be at too lower frequency but you will figure it out. ?Try anything, it will either get better or worse.

Hi,

Usually I'm bothered when I see a transistor amplifier without an emitter resistor. The gain should be set by the ratio of the collector resistor to the emitter resistor and be set significantly below the gain of the transistor. This is so things will be stable and you can do large production runs of products and not have to stop production to determine how to fix the product (or add adjustable pots that will cost labor time to adjust) every other time you get parts from a different supplier or batch. The other important thing the emitter resistor provides in stability of the bias point of the transistor. As the emitter provides a negative feedback based on how much current flowing through the collector. This works to keep the voltage around 1/2 the Vcc with wide variations in the gain of the transistors.

In the case of Q70 the next stop for the audio is a volume control, so if the gain is higher or lower in various batches, so be it. Likely nobody will notice. In the case of the "wide open" Q70 it is important to note that the bias resistor is connected from the collector to the base. That is an alternative form of negative feedback for keeping the bias level from going out of bounds.

If a batch of transistors with higher gain were used, the gain of the transistor would tend to want to conduct more and drive the collector voltage down. Maybe so close to ground, the amplifier would not work. But, the collector voltage goes down, also reducing the bias current. That limits how far the collector voltage can go off from the optimal middle point. Low gain transistors would be the same idea but the reverse would happen, keeping the collector voltage from going too high from center. The impedance of the audio feeding Q70 from the mixer is low enough that the 100K bias resistor should not provide much negative feedback at audio frequencies and lower the audio gain.

It is surprising that higher gain transistors did not make a noticeable difference. Although they would need to be more than twice the gain to be noticeable to the ear, per common wisdom. Maybe changing Q70 to a darlington and adding an emitter resistor to tame it down some might work.?

Another thing that has been discovered by folks that have had low transmit power, or trying to boost it further, is the supply voltage (especially below 12/13 volts) has a major effect on the obtainable transmitter power. A large contributor to that seems to be that the gain of the IF chain drops significantly below these voltages. As the same IF chain is used for transmit and receive, running those circuits at 9 volts may be a problem. Your measurements on your radio will let you know if this is an issue.

Tom, wb6b

Yes Sarma -- I'm sure there is some extra noise someplace due to using the switching regulator.?

On the other hand, I also gained an extra voltage display, which I love, and I got to solder a new board into the mix, which I love.

If I ever run on battery power, I will feel really smart for using a switching regulator and not a power hungry linear regulator. (actually, I may never do that, but just in case...I can say I planned ahead. Which is totally untrue, it just worked out that way.)

And as an extra bonus, nothing blew up -- which I also love.

Don
km4udx??

Arvo -- there is no desired adjustment of the gain due to the extra voltage.? That is the goal of the few extra volts...to get a few extra watts.? You most defiantly do not want to adjust anything...just let the extra volts do their magic thing to the finals and bask in the glow of accomplishment.?

Having said that, I did adjust the PA bias per instructions when I first got the rig and used a 12v wall wart for the the whole radio.? Did I need to do that? Na...it was set fine from the factory, I just wanted to hook up my meter and see what every body was talking about. I've never set the bias of anything in my life, never mind two little plastic/metal thingies in the back of the board.? So I used the meter and twisted the little driver pot till I got the 100ma. I even did it a few times just to show off to myself. hahahah. I'm easily impressed. hahaha.

Anyway, there MAY be a case for adjusting the PA basis when you (me) use a higher voltage, I have no idea and didn't look it up.? But I'm not going to mess with it regardless. Having flown high to the sun with my first successful PA bias adjustment, I have zero motivation to try my luck again. hahaha. [but typically I will mess with something until I break it, then I figure that I now understand what is going on...well sort of..hahah]

Now, I did bolt on larger heat sinks (hack sawed from a ancient Pentium CPU heat sink), and I'm glad I did -- given that I left the TX on full power for 15 minutes while in stupid mode (a new digital mode for the inattentive and easily distracted).? Things got all Chernobyl on me, but everything recovered.

So the heat sinks and fuse were the only adjustment I made to accommodate the higher voltage.?

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Thanks Gary.
Vince

Dear Mr. Gordon Libby.?

It pains me to say this, and I hate to admit it publicly, but you are exactly correct. Hahahah

Neverthelss, I for one, will take (and give) all the help I can get. My noggin is a wicked incomplete space. ?A humble vessel ready for the wisdom of others. ?

But, back to your observation, I humbly acknowledge your very good point. ?Well said.

i slink back to the bench....


hahahah.

don
km4udx

Q: ? I did tune to 10.000 - no tone.? The tone is on 10.002.100 on my radio.? So first step - what do I change to get the frequency to display accurately???

A: ?when you tune to 10.002.1 you hear a signal on 10.000.0. ?So your display freq is too high. ? You need to shift the uBitx receiver down by 2.1k. ?How? Change alignment # bit by bit until uBitx display freq equals 10mhz and sound is sounding there. ?Go into setup, find the alignment value (sorry I forgot what the menu calls it), and add a negative 100, save it, ?and retune. Are you closer or further off? Repeat as required.?

The discussion of using fldigi as a specterm analyzer is very clever, but too complicated for now. ?One problem at a time, says me. ?

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Transistor Q 70 is operated in a very simple low level amplifier configuration. ?That’s a very simple biasing arrangement, identical to what we used in our VOX circuitry in our home brew Signalink ?equivalent ?digital interface

That's a cool idea - that would give me a way of determining the existing and desired amount of gain, which takes me back to the desire to reconfigure Q70 stage gain...

I suspect Q70 and it's two biasing resistors (one in C-B path and one in C-Vdd path) have gain controlled by the two resistors (when I changed to a higher-gain transistor type, the circuit gain barely changed), but I've been searching and so far haven't found a model/analysis of this sort of amplifier stage, even though it's really only 3 parts (!)

Dave

Hi all, read up on some of the mods for my BITX40 and one I have made is on the tuning pot. I have replaced the said single turn pot, with a 10 turn pot, to aid tuning accuracy.

My problem is, I have used the wrong value. I should have used a 100k pot, but I replaced the original with a 10 turn of the same value. this makes the frequency gallop at each end of travel.

My question is, can I use a 10 turn wire wound pot? These are quite cheep and easy to obtain and as it is only changing the frequency of the arduino, I think, they should not matter if not carbon made.

Thoughts please and if I need a carbon any links to obtaining these in UK in less than 100s parts please.

thanks Vaughn

An old designers trick: When I'm not set on the exact amount of gain I need for a stage that operates at less than 1 MHz, I pop in an LM324 op amp with a variable feedback resistor and adjust it to where it needs to be to make the next stage work properly. I then can calculate the gain that works (measure R1,R2) and design a transistor circuit around it. Of course, you can just leave the LM324 in place too...