Hello Rob,

I have the same situation and was looking at a simple solution too. Here are my thoughts based on your idea.

Have a look at this page for examples:?http://www.k7tty.com/development/electronicprojects/Diode Switching Circuits.htm

Instead of using +/- voltages for switching I would use a voltage divider, say 1/2 of Vcc (say 47k and 47k) off the 5v from a regulator on the common output side and use the ptt signal from each ptt source for switching through a 22 to 47k biasing resistor to ground on the input side. On the input side I would connect each diode to the +5v via a 100k to 220k resistor.

That way with all PTT off you get reverse bias of +5 - 1/2 of +5 = 2.5v of reverse bias, and with ptt on you get +5 - 22/122 * 5v/2 = 1.6v of forward bias (if using 100k and 22k resistors on the input side).

Since you are dealing with max audio signals of around 100mv the biasing should keep you cleanly in the on or off region.

The output impedance of the electret is a few k ohms so small enough compared to the biasing circuit values.

For the logical OR of the ptt inputs I would use a pair of schottky diodes (e.g. Bat46) since the ptt input on the nano is an analog input (A3 pin) and the threshold for ptt on can be changed in software.

I would take care of stray RF which would cause issues with these circuits (screened cables, good ground, decoupling capacitors and ferrite sleeves if required).

Hope that helps,

73, John (VK2ETA)

Interesting idea.? After some quick sketching, I think it could be done with 3 capacitors, 3 resistors, 4 diodes, and a Nan gate (Not And).? I have not worked out the details, but here is a rough diagram in the attached PDF.

I do not have a selection for the diodes.? You do want diodes with low forward voltage drop and high reverse resistance (Schottky?).? ?The resistors are to provide enough forward current to ensure that the AC signal will not be clipped.? I would check your diode selection and adjust accordingly.?

If the Nan gate cannot handle the current, then use the third gate as an inverter driving a transistor or MOSFET to switch the computer audio diode.

A potential reference :


Please verify before building, as this was early morning musing, and I am not confident that I have thought through all of the requirements.
73
Evan
AC9TU

I have successfully used a dpdt arrangement. The center goes to the radio and the switched inds going to the mic/soundcard speaker and the other to the speaker/sound cardmic.

One uBITX used a regular pushbutton dtdp switchsalvaged from something and the other a relay controlled by a spst switch.
Neither used any electronics
--
73
Dave

Well this week I got this in the mail, and it had stuff skittering about inside the (banggood?) case when I unboxed it. (Always a bad sign!). First thing: off with the cover. Bits rattling around are 3 odd balls of solder, and a blade off the fan. (Shrouded, not sure how it would get broken in shipment, but who knows.) Any way, here is what I know. It's off frequency about 1.75 Kc or so on 40M, it will go into TX with supplied (included in this sale)? hand mic, but NO power output. NO power output in CW with a key, but it does go into TX. Receive seems to work fine, although a bit off Freq, as noted. Fan is variable with a pot on rear of case, and it works great, but now unbalanced, so vibrates the rig.... I will send the broken blade, maybe simple super-glue fix? Hooked USB to my old Linux laptop last night, and I could get FLDIGI to recognize the rig, and see signals on waterfall with cord from phones jack on rig to PC mic input. From non-smoking homes. This thing is ALMOST really nice. More good news is, I bet someone can fix it pretty easily. Bad news- it won't be me. Not interested, nor capable. It was advertised as in good working order, which is why I bought it. Looking to recover some of my $$. Will ship DOUBLE BOXED this time, to lower 48 only for $120. I take PayPal only.... would like this out of my life.
Contact me via an "I'll take it" here, or via QRZ listed email.?
Greg, KC8HXO

Hello!

So I want to have a separate line-in for my uBITX, separate from the Mic input.? I also want to have a separate PTT.? The intent is to have the regular mic/PTT plugged into the front of the radio, and then also have the computer hooked up in the back.??

Requirements/Constraints/Desirements:
- Always keep the computer plugged in.
- Always keep the mic plugged in.
- If the mic PTT is pressed, don't transmit computer audio.
- If the computer PTT is asserted, don't transmit mic audio.
- Don't require a mechanical switch between the inputs (I have a fairly compact case and don't have room for more switches).
- Don't require a relay*. (* This is not a hard requirement, but I'd rather not use a relay if I can help it.)
- Don't require use of any Arduino pins (I'm using parallel display, don't have anything available.).

I was looking at schematics for some old Ten-Tec Omni V rigs, and saw the diodes in the transmit audio line, where a pair of diodes was alternately forward/reversed biased to route the audio either to the speech processor, or not, and I thought, maybe I could use a similar diode arrangement to enable just the audio from the mic or the line-in... except that they switch the bias voltage to the diodes via a front panel switch, so still a problem to solve.

So my thought is, in the "default" configuration, only the Mic audio would be routed to the uBITX.? But, IF the rear panel PTT was activated, then only the Line-in audio (for as long as the rear panel PTT is activated).? Any thoughts on a circuit--preferably simple :-)--to achieve this?

Thanks!
-Rob KC4UPR

Richard

Audio is scarce with a v4 using a speaker, much better with headphones. Any external amplified speaker you can find should help. For cw an audio filter with narrow bandwidth is a big help. If you can build a cw audio filter, check out various qrp merchants and clubs. Not available last I knew, but I use a necaf with my v4.

73 curt

Ahem,

Fuses were not developed because of one mistake that one person made 125 years ago! Get and install the fuse as close to the power source as is practicable. The kits do not come with a fuse nor a fuse holder. They are not expensive. Just do it.

73,

Bill KU8H

Retired Firefighter

--
bark less - wag more

Different Hams have different views.? One of the RF Engineers on this board does not use fuses for anything other than keeping a fire from happening.??

I would recommend a fuse more than 3 amps and less than the wire size can carry that you are using to power the rig. I use 3 amps, and it has saved me a couple of times that my fat fingers sauced a short that could have taken out some other components.? You diffidently want a fuse IF you are putting in the reverse voltage protection diode across the supply lines as the HF Signals assembly instructions suggest.?

73
Evan
AC9TU

The polarity will be correct, but where are you switching the power?? Do you plan to use the switch on the volume control supplied with the v4 and v5 kits?? Also, are you planning to do the reverse voltage protection diode?? Fuse?

From what I can see of the board, it looks like a v4.

73
Evan
AC9TU

They can be.? The BFO is used for both receive and transmit signals.? If the BFO is used to generate the sideband signal with the filter to remove the opposite sideband.? If the BFO frequency is too close to the edge of the SSB filter, I have seen the carrier "bleed" through.? I did tests using an RSP2 SRDPlay and the RSP Spectrum Analyzer software to see what the signal was like.? When I adjusted the BFO to minimize the carrier, the sound was tinny.? When I adjusted the BFO for a more pleasing sound, I had a residual carrier, AND the volume was lower.? The filter is fairly narrow and has sharp skirts.? This means that if not centered correctly it will cut off some of the signal.

I have performed this test on only one v4.? That was because I was having issues with that balanced BFO mixer and was trying to verify that the diodes were not the issue.

The speaker could be another reason for your low volume.? My v5 is driving a 4 ohm speaker with good results.? Both of my v4 require audio amps to drive a speaker.? Those are TDA2030 modules from eBay.

Above is my analysis.? It could be in error.? You can wait to see if others have any suggestions.
73
Evan
AC9TU

My first guess would be that you need to set USB or LSB mode.? The second would be the PTT on the mic is not wired correctly, or the switch is broken.? I would take a spare 3.5mm TRS (Tip Rind Sleeve) Plug and insert it into the Mic/PTT jack.? Short the ring to sleeve connection and see if the TX light comes on then.? If so, then the PTT mic switch or wiring is the issue.

Above are just guesses on my part.? I have 3 v4 and 1 v5 but 0 v6 ubitx.

73
Evan
AC9TU

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Jim:

Hi Dave,

i never thought to use to use this approach. Matter of fact, have a set of amplified speakers in storage. Currently using a non-Amplified speaker box with very marginal results. I know my XYL is very tired of seeing me work on this project, and others. Her response has been, ?"why don't you buy a "good" radio and enjoy it?" My response has been "Well, want to use what I have, and not put out more money for another unit." Do have the trusty TS-440SAT in the shack since about 2000 or so. Did try a XIEGU G1M but it suffered a power event failure, and is buried in it's box as unrepairable.

73,

Wes/KH2EE

Hi Vic,

Thank you for your lead in QST. Will gave to do the research. Not really handy building things with sight declining. Last project cost more in rebuild time and parts than the inop unit was worth. I hate to tell you the actual amount of time spent on building the V4 that was supposed to be an evening project. Still not satisfied with my calibration results either. Getting older has it's downside too.

Hi Rubens,

Thank you for the lead. Will check it out!

73,

Wes/KH2EE

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