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On Sat, Sep 7, 2019 at 06:59 PM, Jerry Gaffke wrote:

Here's a 2018 treatment of T/R switches by W7ZOI, the Kang approach is figure 1:
? ??

A quick look at this article looks very good. I'm in the process of learning the Eagle Schematic capture and PCB design package. That package includes Ngspice. I can use the LTSpice schematic included in the article as a practice exercise for learning Eagle and Ngspice. As well as more about the operation of the T/R switch.

Just a thought though, if you were willing to comprise a little attenuation of the receive signal into the receive circuit and waste a little heat in a resistor while transmitting, maybe just using a resistor to limit the current flowing into the back to back diodes and a series resistor to the input of the receive circuit to keep the current there well below what would damage the receiver input, would work. That would work for a multi band transceiver.?

If you don't force the input of the receiver first stage to be 50 ohms and let it be significantly higher, the main resistor from the antenna connector to the back-to-back diodes could be a fairly high resistance. At HF the noise contributed by the receiver first stage is low compared to the main source of atmospheric noise, so a little signal loss wold not be a problem. (Of course, the answer to this is probably already covered in some part of these linked articles I have not read yet.)

I image there are receivers out there that don't bother to to supply 50 ohms, on receive, to the antenna terminal. I wonder how far you could deviate before the coax could create a 1/4 wave notch filter. I'm sure I'd end up cutting my coax just to the length so it would be a perfect 1/4 wave length at my favorite net's frequency.

Tom, wb6b

Reversing the power supply into the board can blow a bunch of stuff,
and thus be hard to fix.
But the fact that the Raduino works at all is a very good sign.

The Raduino is usually dead in the water after an event like this.
It is still possible that it is partially damaged (blown IO cells into the Nano?).
If a friend also has a uBitx, maybe try your Raduino in his uBitx to see if it works.
But it might have to be a very good friend.

If the encoder is wired up properly and the encoder did not come defective,
it should cause the frequency shown in the display to change.
If that does not work, check your wiring closely.
You can verify that the encoder is working properly with an ohmmeter,
disconnect it and measure the resistance from terminal A of the encoder?
(as shown in the wireup diagram) to terminal C.? It alternate between
open (thousands of ohms) and shorted (near zero ohms) as you rotate the knob.
Then do the same for between terminal B and terminal C.

If PA-PWR (the +12v into the IRF510 finals) got a reversed supply, then
look hard at L9 and the traces from it to the IRF510's and the PA-PWR connector.
Either L9 or the traces will fry, but probably not the IRF510's.
That could well be the source of your smoke.

With any luck at all, anything on the TX rail did not see -12v, only the RX rail saw -12v.
Most of the stuff that the RX rail goes to is pretty well protected by resistors, limiting current flow.
The LM386 at U1 and/or R71 could have blown, the 100 ohms at R71 would have limited currents
into U1 to 120ma absolute max but that's quite a lot.
I suspect most of the transistors would survive due to the nearby resistors, maybe all.

Once you prove out the Raduino somehow and have U1 working to where there's
a hiss in the headphones, you might try Farhan's procedure outlined here for the Bitx40:
? ??
Farhan is using a piece of wire maybe a meter long as an antenna to pick up
local QRM (digital clocks, microwaves, atmospheric noise)
and inject that noise into various parts of the receiver.

This could be very challenging to get working again.
Or you could be lucky.

Jerry, KE7ER

On Sat, Sep 7, 2019 at 06:59 PM, Jerry Gaffke wrote:

Kang approach is in fig 2 of the W7ZOI article pointed to by post??/g/BITX20/message/70861

Hi,

That?Wes Hayward article is pretty good. I'd recommend people read it, including myself.

I think at the time I found that article we were trying to figure out just how much like a PIN diode the 1N4007 rectifiers behaved. And if 1N4007 diodes from different manufactures might be different in regards to the "PINness" of their diodes. I skimmed right past the "Resonate T/R Switch" description.?

Tom, wb6b

After I posted my replay, I read Jerry's recommendations.? I like the second receiver test for the BFO to verify that the Raduino RF section is working.? I will need to remember that for future references.? You can do that when powered by the USB connection as the Si5351a runs off of the 3.3v rail that comes from the Nano.

Another possibility for the source of the smell is it came from the volume control.? If you truly put 12v across it, and the wiper was close to one of the ends, you could have smoked it.? Since the resistor is behind a metal case, you may not see it without close inspection.? Run a resistance check on it as well.

73
Evan
AC9TU

Hi Jerry,
i am using the amateurradiokits.in enclosure, which comes with some extra items to wire up connections, one of which is a three pin connector for volume. What happened was that the red and black wires on the 12v power supply to the board were reversed, maybe 15 seconds of power supplied before I cut it.

i adjusted the contrast and the display is working and shows the frequency, although the encoder doesn’t seem to change the frequency. I am going to disassembly, check all of the solder joints and see if I can see any obvious visible damage to any components. Right now, I don’t see any, other than my on/off switch, which needs to be replaced since I need to hold it in to maintain the power on to the unit.

Gus,

As a potential way of isolating the fault, you can unplug the Raduino from the main board and run the Raduino from a USB port on your computer, or other 5 volt supply.? That would let you know if the display and Nano are OK.? If you do this, you do not need the controls connected to the 8 pin connector on the Raduino.? plug a microUSB cable into the Nano on the RAduino and into a PC or other USB 5 volt source.? The display should light up, and you should see the normal startup screen.? If I interpreted your description, you put the 12 v power to the volume control connections on the uBITX board.? That could have taken out the Nano on the Raduino, as there is a connection to the Nano for CW side tone.? The Nano does not like anything over 5v or under 0v relative to the common on the Nano.? Nano's are cheap, so no big deal if you need to replace it.? Just make sure that you get one WITHOUT the headers already soldered, as they need to go on the other side of the board to work in the uBITX.

If that does work, then the Raduino is Probably OK.

Going beyond that will depend on the test equipment that you have.

By the way, did you do the test in step two of the wire up instructions from HF Signals?


I would do that test to verify that the board is still operational.? Note that the Raduino is NOT installed when measuring the current.

73
Evan
AC9TU

Gus,

This is not very clear to me:

>? However, I mistakenly switched two of the three wire cables.
>? The one that I used for the power was supposed to be for the volume control.
>? Normally there would not likely be an issue but for the fact that the way
>? the connector attached to the board, the polarity was actually reversed?

The volume control on the uBitx is wired up to an 8 pin connector,
the power supply goes into a 3 pin connector.? Would be hard to swap them.
Exactly what pin did you connect the +12v wire from your power supply into?
Exactly what pin did you connect the ground wire from your power supply into?

It is possible for those caps to be damaged by reverse polarity.
But if?you see no apparent damage, they are probably in good enough shape.

Reverse polarity on the main +12v rail will pretty much destroy the Raduino?
and also blow a bunch of parts on the main board.? That would be difficult to repair.

I think I would first try to get that Raduino working.
You can unplug it from the radio, feed it between 8 and 12 volts, and see if you can?
get the display to work.? If the display works, see if you can hear the BFO by tuning in
a nearby shortwave receiver to 11.059mhz, listen for a clear CW tone with a piece of
wire for an antenna from the receiver coming within a couple inches of the Raduino.
If the display works and you can hear that tone, the Raduino is fine.

If what you did was wire your power supply into VOL-M and/or VOL-H and/or Ground
(the three volume control wires), I'd think the damage would be limited to the LM386 at U1.
Do you see obvious cracks or craters in the case of U1?
Q74 might have been hurt, but I doubt it.? There is a possibility that a negative supply on VOL-M
could have gotten through the LM386 into the +12v rail, but the 100 ohms at R74 would
somewhat limit the current available for wrecking havoc.
?
Jerry, KE7ER

Tom,

The Kang approach is in fig 2 of the W7ZOI article pointed to by post??/g/BITX20/message/70861
That article mentions Roy Lewellen, W7EL, and his "Optimized Transceiver" in the Aug 1980 QST
as a possible source?for what W7ZOI considers this "standard" T/R switch.
Here's a 2018 treatment of T/R switches by W7ZOI, the Kang approach is figure 1:
? ??

Oh, and post 70861 was from Tom, WB6B.
I've probably seen the circuit over the years as well,?
never quite realizing how it worked.

Jerry, KE7ER

Thank you, Mark. I do have the 4.7k ohm resistor installed and I will try to adjust the contrast as well. Perhaps that will fix the issue, save for my switch, which is not functioning and needs to be replaced. If not, I will try to swap out the caps, but hopefully the very short application of reverse polarity didn’t totally damage them. I appreciate your response.

-Gus
W9SSN

On Sat, Sep 7, 2019 at 06:34 AM, Jim Willis wrote:

IBM Huntsville, they showed me their navigation system comprising three microprocessors “voters” and an analog “patch panel” navigation computer. ?I was hooked!

I can imagine what that was like. I did not work in the space race, but, as a kid, a friends father worked for Autonetics and he would bring us to their employee open house events and we would get to see all this amazing technology set up on display in various labs. For a kid it was mind boggling to see this stuff and in many lucky instances, someone was there to try to explain it to a kid.?

I just looked at this video where a new tech person gets to talk with an IBM Huntsville engineer from the day. He really seems to get a feeling for the technology of the day and the amazing things accomplished at that state of the art.



What it must have been like to thrust a monstrous machine off the earth with a huge controlled explosion, with a control technology that had a main program loop cycle time of two seconds, to actually keep this monster on track.

Tom, wb6b

Hi Gus,

Well, if you smelled something then likely something got a bit too hot!

A couple notes:

The black squares on the display is normal if you haven't adjusted the contrast for the diplay yet (small smt pot on the board).

Looking at the schematic I notice two places where reversed power will end up with a circuit with electrolytic capacitors hooked up backwards.? Check the schematic for these (one is the power line to the lm386 audio chip -- the other is nearby).? Electrolytic capacitors don't like being hooked up backwards and are likely permanently damaged.? I would replace them with similar value parts.

You should get a good magnifier out and a strong light and examine both boards well for burnt traces.?? If you find any, note any parts connected to the traces as they may need to be investigated for damage.

Make sure you have the CW key resistor in place -- the board will stay in transmit and never go to receiver unless this is installed.

Finally, see recent posts about reverse polarity protection :-0

73,


Mark.

Thanks much Mark..
--
John - N0CTL - Fulltime RV in a 40' motorhome

On Sat, Sep 7, 2019 at 08:28 AM, Jerry Gaffke wrote:

For single band use, Kang's TR switch is very simple:

That is an interesting circuit. So it looks like the series resonate circuit is a low impedance at 40 meters passing the received RF to the receiver amplifiers. Then, when the transmitter is keyed up the diodes begin to conduct and the effective low impedance of the diode in that situation, disrupts the series resonate circuit and the transmit power into the switch circuit now only/mostly sees the relatively high impedance of the 52 PF capacitors and the voltage the receiver needs to withstand is limited by the clamping function of the diodes.

If I interpreted correctly how this circuit works, very clever. Actually, if I didn't interpreted it correctly, still very clever.

?/g/BITX20/topic/32744828

Tom, wb6b

i was excited to put together my Ubitx today after finally getting a roll of .5 mm solder yesterday. I’m not an expert by any means in electronics assembly - I’d say that my proficiency is probably 33 on a scale from 0-100. Anyway, I assembled the components and put the radio together. However, I mistakenly switched two of the three wire cables. The one that I used for the power was supposed to be for the volume control. Normally there would not likely be an issue but for the fact that the way the connector attached to the board, the polarity was actually reversed (I should have double checked this but I didn’t since I was excited to power it up). Of course, when I switched on the power, an acrid odor was produced. I immediately switched off the power and noticed the issue and swapped the wires. Powered up the radio after the correction and the display flashed green with all black boxes and then powered off (note I have a push button power switch installed). If I hold the toggle switch in, the display stays on but had the black boxes across the display. I suspect the switch could be bad, but I’m also worried that the reverse power fried something. There is no visible damage but that doesn’t mean there is no damage. Any thoughts would be appreciated.

Gus
W9SSN

I really could use a good reference for a long lasting replacement relay for the uBitix transimit/receive relay, what say you ?

John,

If you are looking at the 5" Nextion files under AJ6CU, then I was probably the last person to touch them. Unfortunately, I couldn't find any of the graphic files either when I made all my mods to the 5". I assume you found the export function on the Nextion editor? That will at least get you the png/jpgs. Not vector...

I did a quick search of my computer and zipped up and attached the psd/png files I found.

Let me know if I can help in anyway. Although this was a fun project programmatically, I am definitely not a graphics or UX designer. Becareful of any of the graphs, they are actually drawn with Nextion code and if you start moving graphics around you will need to adjust the offsets.

73
Mark
AJ6CU

As John, K0JD pointed out in post
? ? /g/BITX20/message/70894
the TenTec Argosy was using rectified RF to create the high DC voltage
required for a PIN diode T/R switch.? As proposed in post 32109 some 30 years later.
Later in that Argosy discussion we find that two of the diodes in the manual are drawn backwards.

If I were to do T/R switching for the uBitx, I'd first try something like what's in the Argosy.
For the Bitx40, use Kang's much simpler single band solution.

Jerry, KE7ER

Correction:??
Second paragraph here mentions it plus a couple other options with regard to TR switches:
??/g/BITX20/message/39746

Jerry, KE7ER

Tom,

You need to poke around a bit further on qrpkits.com
? ??
Schematic is in that first assembly manual listed.

Second paragraph here mentions it plus a couple other options with regard to TR switches:
? ??

For single band use, Kang's TR switch is very simple:
? ??/g/BITX20/topic/32744828
But the inductor and cap must be series resonant at the freq of use, so won't work on the multiband uBitx.

All of these T/R switching schemes have been around for decades.

Jerry, KE7ER