The KCRC TechNet Puzzle for January 24, 2018

 

What does this interesting bit of electronics in the middle look like to you (please don’t just “Google this all at first – think about it for just a while)?

Is this a…

A   Copper Snake
B   Hairpin Filter
C   Bias-T
D   Copper T

(and what the heck might it do????)

 

The KCRC TechNet Puzzle for January 10, 2018

 

Over-driving a power amplifier will…

A     give a high SWR
B     give minimum distortion on receive
C     generate excessive harmonics
D     maximize the power output

 

And now for the answer to our January 10, 2018, TechNet Puzzle

(It is in “invisotext” and will be visible if you highlight the area below!)

Let’s take your choices one at a time:

A) SWR (Voltage Standing Wave Ratio) is a consequence of an impedance mismatch in your antenna system. Although the calculated percentage of reflected power, that many SWR meters use to calculate your SWR is affected, to a degree by your final power output, overdriving your final power output should have no effect upon your antenna system’s SWR, so this one is wrong!

B) Overdriving your final power output stage should only affect your transmissions, not your reception (they are separate circuits inside your transceiver’s block diagram), so this one is wrong, too.

C) This one is a quite reasonable answer, so let’s hold on to this one!

D) Although overdriving your final power amplifier MAY lead to a great power output, it does not necessarily accomplish this (it depends upon the circuit and component choices, so this one very “iffy”

Power amplifiers are usually designed to squeeze as much power out of a design as possible – it’s just good economics, people like MORE power. The problem is not only that a circuit has a maximum gain/maximum output, you are also trying to use your circuit at a power level where it produces a LINEAR response gain. Past this region of LINEARITY, you get a very bad NON-LINEAR response that not only generates distortion on your intended frequency but generates so much distortion that it “leaks” through your amplifier’s filters, to blanket other frequencies with your splatter/noise. This used to be a BIG problem with some CB-ers – they would have their final amplifier input resistor’s resistance decreased, increasing the circuit’s gain, at the price of non-linearity, distortion and out of frequency emissions, but hey the wattmeter looked great!

As you have gleaned by now, the correct answer is/was “C”, excessive harmonic noise!