Hey Jerry, I’ve had strange things like his happen to me with other equipment when transmitting even with a little Power like the bitx40. ?I’ve zapped the inductors on a SpyVerter and SV1AFN upconverter, fried them completely, the spyverter has board damage too but nothing else, no other components. Heck, I’ve fried the SV1AFN a few times with my 100w radio and finally beyond repair because it killed the mixer and too many things I didn’t have parts for. ?My SDR Antenna is near my long wire TX antenna I use for my Yaesu and the bitx40 when I had it.?

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It happened mostly when I was tuning up, actually I think only when tuning up. And especially on 160. I’ve watched an inductor burn up right before my eyes when the tuner was chattering. Must of been throwing high voltages everywhere. RF sure is amazing lol. I’m still learning.?

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That's looks great if you want a high impedance probe for your oscilloscope or spectrum analyzer.
RF goes in, bigger RF at the same frequency goes out

But that is not a suitable RF probe for a DVM, where you want RF in, and a DC voltage out
that represents how strong the RF in was.

There are some similar AD8307 probes available on Ebay that I previously pointed to?
in response to one of your posts, they look much more suitable though I have not tried them.

Jerry, KE7ER


On Sun, Feb 11, 2018 at 02:45 pm, Joe Puma wrote:

I’m waiting for this to come in the mail: RF Active Probe 0.1-1.5GHz? analyzer oscilloscope

would be between 100 and 3000 hz, and perhaps sound a bit tinny.

Oops -- I noticed you said "tinny when
monitoring in another receiver..."

That would rule out the BFO in YOUR receiver.

It could be the voice quality of your mic amplifier.
There have been various solutions posited for
that, including Kang's replacing resistors in
the amp. He also noticed a similar thing and
posited a larger solution. See his website
Small Wonder QRP for clues.

I’m waiting for this to come in the mail: RF Active Probe 0.1-1.5GHz? analyzer oscilloscope

Good advice, build a diode RF probe.
A germanium diode such as the 1n34a or 1n60 works well, but they are expensive now and hard to get.
A schottky diode (such as the Bat54s used on the Bitx40 diode mixers) works reasonably well.
A standard silicon diode such as a 1n4148 might be good enough for measuring fairly high RF power nodes?
such as at the antenna port of a working transmitter, but definitely will not see the expected RF voltage at the base of Q13.
The issue here is the forward voltage drop for small currents, perhaps 0.3v for the Schottky and 0.6v for the 1n4148.

The germanium diodes will be less than the Schottky but dependent on temperature.
The datasheet punts, and says 1 volt max at 5ma, should be good down to 100mv or so with the currents involved in an RF probe at 10megaohms:
? ??
? ??

N5ESE tries to explain the probe, but only goes so far.
That RF probe design assumes a voltmeter with an input resistance of 10megaohms,
some DVM's will have an input resistance that is considerably less.
So don't count on that probe reading RMS voltages accurately until somehow calibrated.
As the RF voltages approach the forward voltage drop across the diode it will become less and less accurate,
though can still be surprisingly useful (perhaps with a calibration chart) down to a few tens of millivolts if you have the right diode.
Also, N5ESE fails to mention that the capacitance between the probes into the DVM is an integral part of the design,
that capacitance along with his 4.7megaohm resistor forms a low pass filter so that the meter sees DC instead of rectified RF.


We should have a spare Bat54s plus cap and resistor into an analog Nano pin,?
so we can all have a common way of measuring RF voltages when debugging.
With different diodes and different voltmeters, we will all get different results and cannot usefully compare our measurements.

Jerry, KE7ER



On Sun, Feb 11, 2018 at 01:14 pm, M Garza wrote:

Since you do not have a watt meter, and you have a multimeter, you could build a rf probe.? You can see the rf voltage and calculate the wattage.

Here is a link to one you can build.? It is very easy:

?

From the photo, looks like a burned trace from C6 to L3.
From the Bitx40 schematic it's hard to imagine how that might have happened.
That node is isolated from other parts of the rig that might have significant DC power by multiple DC blocking caps.
RF power there should be milliwatts, even with a nearby QRO transmitter.
Even a loose wire with +12VDC on it striking that node would not blow the trace since there is no path to ground.
L3 is a toroid and thus inherently well shielded, I doubt significant RF was coupled directly into L3 somehow.

Could be that all you need to do is fix the trace.
But the cause is totally unexplained, and something with enough power to scorch a trace like that has enough power?
to blow out many other things.? Fixing this might require finding somebody with a scope and bag of spare parts.

Do let us know what parts had to be replaced once you get this fixed.
And any guesses as to how it happened.
For me at least, truly a mystery.

Jerry, KE7ER

On Sun, Feb 11, 2018 at 08:41 am, Gordon Gibby wrote:

Looks like L3, and possibly other series elements in the 40 m filter got way too much voltage. You’ll probably have to use an ohmmeter to test out each connection and see what has become non-conductive. ?I suspect Q 13 got fried in the process, and there are two other transistors that would’ve been connected that might’ve been damaged as well from the schematic. ?With some care, these can be replaced by ordinary 2N3904 transistors.

?

Since you do not have a watt meter, and you have a multimeter, you could build a rf probe.? You can see the rf voltage and calculate the wattage.

Here is a link to one you can build.? It is very easy:

?

Should be plug compatible, but note that I've found that different
brands/colours of 1602 displays may be slightly differently size, so it
may be too tight or sloppy in your existing front panel cutout.

Mike ZL1AXG

On 12/02/18 6:56 AM, VE7WQ wrote:

Is this plug and play for the raduino?
3.3V/5V 16X2 1602 Character LCD Display,
White on Black,High Contrast
US$2.80 In stock

--
Mike Woods
mhwoods@...

After some other testing on a BitX40 that was working well, it is likely that 12v (or even 24v) touched one of the speaker leads. Now I have essentially no audio out from the radio. On very strong signals and at maximum volume I can hear a weak and very distorted sound out of either the speaker or a separate speaker/mic, but it is not copyable and only just recognizeable as a signal. Listening on another receiver and watching the output, transmit seems fine. It sounds clear and undistorted and the power out is pretty normal. I checked the voltages around Q16 and they are exactly as expected in receive and transmit. The suspicion to me is that the LM386 has "blown", but there are no obvious marks on the board on any components. Is there someplace else I should look before trying to replace that chip?

As to technique for repairing that IC, if it is the problem, I seem to recall a method that involved just cutting the legs off and soldering them to a new chip. Is that a viable way to go?

While I've never owned a barrel of monkees, it? is hard to imagine that could be more fun than the BitX, but I do seem to get myself in trouble playing with it.

=Vic=

Looks like L3, and possibly other series elements in the 40 m filter got way too much voltage. You’ll probably have to use an ohmmeter to test out each connection and see what has become non-conductive. ?I suspect Q 13 got fried in the process, and there are two other transistors that would’ve been connected that might’ve been damaged as well from the schematic. ?With some care, these can be replaced by ordinary 2N3904 transistors.

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