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

开云体育

Eric,
i have a couple of display protection boards left when you do your JackAl display
de
n2aie
vince

I would appreciate assistance with the 40 please.

After triple checking connections, I fired up. The display was blocks which adjusted with the pot on the Rad board. It was drawing 140ma on idle initially, but seems to have dropped back to 70ma after having been on for a while.

There is a soft hiss on the speaker, but no signals on receive. Put the sig gen near on 7.1, but nothing when tuning, although there was a slight noise around 40 megs when I tuned around with the sig gen. Makes a clack clack noise while tuning which I suppose is the Rad incrementing. Bizarrely, moving the tuning control near full deflection either way starts the freq counter counting on at about 5 KC’s/sec, such that it will count up to 7.5 and back to 6.9 the other way. Tuning control is very sensitive.

Any suggestions of tests would be appreciated. Wondering if I’m just unlucky with a duff DDS. I have a scope and sig gen.

Roger, M0TJK

On Fri, Sep 6, 2019 at 11:12 PM, Thomas Sharka wrote:

https://www.vintage-radio.info/heathkit/

Cool site. Fun to look once again, in the context of the era of Heathkit kits and the early space race technology, the electronic designs I poured over learning electronics design.?

Then think of now, when microprocessors have almost replaced transistors as the fundamental unit of designs. Thinking about what a big deal Ham TV was. Now you have a portable wireless TV camera and video screen in your pocket. And you can talk on it and read the news, too boot.

Tom, wb6b

On Fri, Sep 6, 2019 at 10:51 PM, Ashhar Farhan wrote:

look for the bitx20a manual. It has a Tayloe T/R switching system

Hi,

I found some reviews of the bitx20a. Did not find a schematic, yet. However, I found this CW transceiver designed by Dan Tayloe that has a couple of mosfets to cut off the RF to the receiver section when transmitting.?



Is this similar to what you are referring to with the bitx20a design?

Tom, wb6b