2SC2879 datasheet question

[2NC995]

Below, the input/output chart from Toshiba’s datasheet shows an f1 and f2 of 28.000 and 28.001 respectively.

Is this the same as a two-tone SSB test, and if not, what does it mean?

Thanks to any takers!

 

[543_Dallas]

All that is showing is output power vs input power under the listed conditions. You can see that between 80 and 100 watts the line starts to arch. At that point the transistor is running out of poop and gain compression starts. Once you get to that point more drive will still produce more power but the linearity gets worse and worse.

The 2 tone test would be done while monitoring a spectrum analyzer. This is where the IMD figures come from. There is another graph on the datasheet showing IMD levels at different outputs. Those devices have lowest IMD around 60 watts pep. That will change when you get away from the collector voltage and idle current (bias) they used on the data sheet.

 

[2NC995]

You can see that between 80 and 100 watts the line starts to arch. At that point the transistor is running out of poop and gain compression starts. Once you get to that point more drive will still produce more power but the linearity gets worse and worse.

I run mine easy-peasy and right in the lower range...12w PEP into four, it’s all I can do to care for my Chinese knockoffs, and I figure I wouldn’t gain much anyway because I work most that I can hear running it that way.

I don’t understand the two freqs listed, though.

 

[543_Dallas]

I run mine easy-peasy and right in the lower range...12w PEP into four, it’s all I can do to care for my Chinese knockoffs, and I figure I wouldn’t gain much anyway because I work most that I can hear running it that way.

I don’t understand the two freqs listed, though.

I'm not sure about those either.

It would be interesting to see how the Chinese pills compare but I don't have that kind of test equipment.

 

[Dmans]

While not being a “transistor” guy, I read the symbol preceding the “f=28MHz” as meaning the delta frequency. Possibly meaning tested at 28 MHz +or- 1kHz.
For the IMD graph (in the screenshot below) it would make sense. For the Po -Pi graph, not so much but could be understood as a Harmonic specification of the device??

73
David

 

[2NC995]

While not being a “transistor” guy, I read the symbol preceding the “f=28MHz” as meaning the delta frequency. Possibly meaning tested at 28 MHz +or- 1kHz.
For the IMD graph (in the screenshot below) it would make sense. For the Po -Pi graph, not so much but could be understood as a Harmonic specification of the device??

Ok, that’s interesting it’s noted differently on yours. I’m with you on not being clear what the “delta” may mean in the first chart.

 

[Unit 75]

Ok, that’s interesting it’s noted differently on yours. I’m with you on not being clear what the “delta” may mean in the first chart.

"DELTA" is in reference to the average rate of change of "f" which in this case is 1kHz

 

[Tokin]

I'm not sure about those either.

It would be interesting to see how the Chinese pills compare but I don't have that kind of test equipment.

Unfortunately the hg and dei pills dont compare well to the Toshibas. I remember some years back when dei were testing their pills and they couldnt get them to test as well as Toshibas and im sure the hg pills dont test as well either. Toshiba had the key to materials and design.
The way I see it now that Toshiba is out of the game pill amps are going the way of sweep tube units. You best take care of what you have, drive it easy and make it last with the last of the Toshibas fetching $200+ a pill. At least I can still find nos sweep tubes for $30/pc lol.

 

[2NC995]

Unfortunately the hg and dei pills dont compare well to the Toshibas. I remember some years back when dei were testing their pills and they couldnt get them to test as well as Toshibas and im sure the hg pills dont test as well either.

I don’t personally worry about them making as much power, withstanding the high voltages, or any of the high demands we tended to place on Toshibas, so much as I do knowing what’s different.

Knocking on wood...but my DEIs are working out so far so good. I don’t ask much, but what I’ve asked so far hasn’t been an issue.

 

[2NC995]

"DELTA" is in reference to the average rate of change of "f" which in this case is 1kHz

I was glad to see it in a different format than what I originally posted, so as to give some clues. F1 and f2 that I first saw made it sound like two freqs at once...at least my best guess at the time.

 

[Dmans]

F1 and f2 that I first saw made it sound like two freqs at once

I believe that is exactly what it is. If a 1kHz tone is injected into or onto a 28.000 MHz oscillator, what is the output frequency using USB and LSB?

73
David

 

[2NC995]

I believe that is exactly what it is. If a 1kHz tone is injected into or onto a 28.000 MHz oscillator, what is the output frequency using USB and LSB?

73
David

Thats why I thought a two tone test at first...I figured 28mhz and 28.001mhz would be fundamentally the same as two tone SSB?

 

[Unit 75]

They are talking about the IMD here. I wouldn't use the spec sheet as "the bible" so to speak. Use it more as a general reference only. If you do some research you will find that the test jig Toshiba used for the 2879s had no feedback circuit. Secondly, our radio specifications are measured in dB below PEP and not dB below 1 tone or 2 tones. So you could probably add an additional -6dB to what they have stated on their spec sheet.

 

[nomadradio]

IMD is intermodulation distortion.

A measure of how well two separate input signals remain separate, without mixing together.

If you feed a pure sinewave tone into a SSB transmitter, you get a pure RF "tone", or a carrier out of it.

Two audio tones each with a frequency 1 kHz from the other should get you two RF carriers coming out of a SSB transmitter. In practice, they will mix together at least a little bit. The power ratio of those mixing products to the original signal is what they are describing in decibels.

73

 

[2NC995]

Thanks for all the input on this.

If I have my head around it now, the f1 and f2 aren’t really telling us anything with respect to the first chart, beyond describing a portion of the test conditions, but come into play with the second chart for IMD.

Or, I have it all wrong still. Haha.

Thanks again.