Monitor your Ham Radio transmitter with an oscilloscope

[Scavenger2525]

Great video explanation. Thank you for sharing this knowledge. N2QPP

[spectralcodec]

Neat!



[cogburn2006]

How critical are the 1N34A diodes. I can't seem to find them locally. I hate to pay $7.00 shipping for two diodes that are worth $1.00 each. Can I substitute 1N4003 for example?

[w2aew]

@cogburn2006 Germanium diodes like the 1N34A are best for this, but you can also use Silicon switching diodes such as a 1N914 or 1N4148 with decent results. The output will just be a bit more non-linear. A power diode like the 1N4000 series really wouldn't have sufficient switching time to work well in this application.

[johnmcgiv1]

john, great explanation you are a genius mate could you possibly do a video on how a car key fob works how to program etc .

please keep the vids coming, john

[bonsein1]

This method of generating a trapezoid pattern WILL NOT indicate linearity of the modulated stage, only the linearity of the diode detector. To check modulation linearity, you must sample the audio directly from the modulator and use that sample to deflect along the X-axis. With plate modulation, use a resistive voltage divider off the modulated +HV line to the final amplifier, along with a DC blocking capacitor and additional phase shift correction capacitors across the resistors as needed.

[w2aew]

@bonsein1 Of course. To check the linearity of a modulator, you use XY to look at the baseband audio vs. the modulated output. To look at the linearity of an RF amplifier, you can use the diode detector on the exciter output (X) and sample the amplifier (Y). The video doesn't show either of these specifically, as the comments on the video indicate. The video was intending to show how to use XY, recognizing that this jig won't show linearity b/c both detectors are coupled to the same source.

[metclapton]

Great video there, i am getting my shack done up and gone get my test equipment out and vids like this are good to see and give me ideas thanks, how would you couple a 2 tone signal for 2 seprate generators when checking flat top in SSB ?

[w2aew]

@metclapton You can typically use a resistive summer/divider circuit to combine the two tones from the two generators, and reduce their amplitude to a few mV to couple properly to the MIC input of your radio.

[paulh712]

Great video. One of the most helpfull & useful I have found on Youtube for Ham Radio.

73's DE K3ZW

[w2aew]

@paulh712 Thank you Paul - I'm glad that you enjoyed it!

[radiotech181]

Cool video. Great explanation on using the O'scope. Nice detector circuit.

Thanks for taking time in the making of this video.

73.

[w2aew]

@radiotech181 Glad you liked it!

[nflgun]

Very nice. I've been scouring the web for a circuit like this, CleanRF makes something similar, the RF-SM which is a little pricy for my tastes. Even a search of the ARRL archives didn't reveal any home brew circuits. With radios like the FT-857D that have multiple controls for the microphone audio, i.e. compression level, mic gain, DSP mic equalizer, being able to monitor the SSB RF envelope becomes important in order to properly set the levels. Add in an amplified mic, even more so.

[nflgun]

@nflgun In addition being able to monitor the RF waveform when running BPSK3 would be advantageous since it's difficult to set your drive levels without someone else observing your IMD. Question, what kind of waveform would you get if you drove the Ext. trigger with the demod signal? Any chance you'd consider refining the circuit some and maybe writing a QST article? I think you'd be surprised at the response.

[RadioHamGuy]

Excellent video, thanks and this is just the circuit I am looking for since I want to use my scope for just this purpose on the test bench here now..

[w2aew]

@RadioHamGuy I'm glad you liked the video and found it useful. I hope your project turns out well!

[spymsn]

Hello, congratulations, very usuable device.

What is the max. input power? what is the attenuation on RF port?

What is the max operating frequency¡?

73´s de XE1XNP

[w2aew]

@spymsn The maximum input power for the RF sampler would be determined primarily by the power rating of the larger series resistor. It's a fairly simple calculation. However, for higher power operation, I'd probably change to a capacitive pickup rather than a resistor divider. For the demodulator - it is mostly used for linearity testing, which means it is always on the exciter side, not the amp side. The voltage ratings of the coupling cap will largely determine the max power rating.

[KatzOhki]

Fantastic video. I'd like to see some examples of what to look for in terms of "flat topping" and other errors that show you're signal isn't what it should be.

[w2aew]

@KatzOhki Hmmm - I'll have to try to work on something for that. Sometimes it is hard to create these problems on modern rigs because ALC, etc. do a pretty good job at fixing these problems.

[paraglidermx]

@KatzOhki Just do the cap resistor mod to a cobra 29 and you will see flat topping LOL,,

Looks horrible but sounds loud and clear ;-)

[uploadJ]

Nice demo. Thanks for taking the time to put it together.

-uploadJ

.

[jstrunck]

Thanks for posting this vid! It sure beats a "magic" tee!

[w2aew]

@jstrunck Yes, cheaper too! Of course, a whole lot more attenuation than a magic tee, but that's what we want in this case.

[GalaticTG]

I gotta say I like the look and feel of old oscilloscopes like the Tektronix 485

[w2aew]

@GalaticTG Yes, me too!

[azav8raa]

very cool video. I'm searching component junk box for the parts to build this as I type. Thanks for sharing.

de KB7ZUT

[w2aew]

@azav8raa Good Luck Andy.

[dolphus333]

Very cool!  Thanks!

73 de KD0FNR Hamilton

[jeriellsworth]

Thanks for sharing this. I haven't seen a trapezoid display in years.

[w2aew]

@jeriellsworth You're welcome Jeri. Glad you enjoyed it. I'm thinking of doing a video on probing next...