Electronics > RF, Microwave, Ham Radio

I bet many hams will answer this question incorrectly ...

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xrunner:
"If you set your XYZ FM rig to a power setting of 20 Watts on it's menu display, how much RF power is the thing really generating to make that happen?"

I bet most of them will say "About 20W ... maybe a little more?"

What do you all think they will say?  :popcorn:

I might ask that question tonight on the local repeater.

babysitter:
The common understanding of "power generated" is "power delivered into a 50 ohm load", so if one is not careful listening he might go into your trap.

Most hams will still be aware that there is impedance matching, Zs=Zl with the implication that the source will convert about half of the generated power to heat just for that rule, and also know that there are things like driver level at the input of the PA which has to be generated by preceeding stages that will somehow also not make it to the socket, generally.

Also, clock signals for controllers...

Did I pass your test? :)

Best regards

Hendrik

xrunner:

--- Quote from: babysitter on May 22, 2016, 07:08:21 am ---The common understanding of "power generated" is "power delivered into a 50 ohm load", so if one is not careful listening he might go into your trap.

Most hams will still be aware that there is impedance matching, Zs=Zl with the implication that the source will convert about half of the generated power to heat just for that rule, ...

--- End quote ---

It's easy enough to tell, I just did it. Looking at my PSU for my FTM-100, I'm seeing little current draw on receive, maybe 0.5A.

Well, if it only generated 50W, it would draw about 50/13.8V = 3.6A when transmitting (Yes I know there is inefficiency and some of the RF circuits take a little more power when transmitting). But it draws nearly 7.5A @ 50W

100W / 13.8V = 7.2A, so it basically tells you right there.

What selecting output power on your rig really tells you is the same thing a high-end RF generator tells you when you select PD instead of EMF for the RF output display. PD is the power you get at the 50 ohm load, which is 1/2 the power the RF generator is developing. If the rig had a selection for EMF, it would show 100W on the display (for a 50W output into a 50 ohm antenna impedance).


--- Quote ---Did I pass your test? :)

--- End quote ---

Yep.  :)

KM4FER:
Oh but then the rules talk about Peak-Envelope-Power so which power are you asking about?

What's the relationship between PEP and dial setting?

xrunner:

--- Quote from: KM4FER on May 23, 2016, 04:05:39 pm ---Oh but then the rules talk about Peak-Envelope-Power so which power are you asking about?

What's the relationship between PEP and dial setting?

--- End quote ---

Doesn't matter - PEP (SSB), CW, FM, the RF power amp makes about double the power that ends up in the load (the antenna).

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