Pad vs Trim?

[Ed/KB1HYS]

reading some instructions for aligning an OT reciever. (455khz IF BC/Shortwave).

It says that:

IF ALIGNMENT CONVENTIONAL

Need a little help figuring out what exactly they mean.

SW OSC (K) TRIM AT 18MC
SW ANT (M) TRIM AT 16MC ...

... BC (J) PAD AT 600KC.

Is trim Peak? I assume PAD means adjust for minimum signal?

I'm putting a scope across various stages and making the adjustments.

Using a grid dipper for the signal (monitored by my R-390 to put it on frequency)

The schematic is from a Rider manual (John F.)

[w3jn]

There are trimmers, and there are padders.  Both are what we'd term "trimmer capacitors" ie screwdriver-adjustable variable capacitors.  The difference is where they electronically reside in the circuit.

The trimmer is in *parallel* with the main tuning capacitor.  You always adjust a trimmer at min capacity of the main tuning cap, because that is where the trimmer will have the most effect.  Conversely you adjust the L (if it's adjustable) at the max capacity (ie plates meshed) of the tuning cap.

When the L isn't adjustable, you need some way to peak at the max capacity of the tuning cap.  What you have in this instance is a padder - a "trimmer" capacitor in *series* with the main tuning capacitor.  This has the most effect at the max capacity of the main tuning cap, just like adjusting the L at this point will.

So figure out which variables are the trimmers and which are the padders.  Most likely they'll look identical - find a manual, Riders', or Photofact for the radio for guidance.

[KM1H]

What John said.

Look up the circuits in an old handbook. Without the bandswitch and other coils and caps its easier to understand with just a basic diagram.

Carl
KM1H

[Ed/KB1HYS]

thanks guys.

I've got the schematic & such off of the web. it was the terminology that threw me.

So regardless of the name of the action, I'm really looking to peak the output... which makes sense.

[w3jn]

Yep, always tune for a peak.  Except when tuning the IF output in an amplified AVC circuit - then you tune for min.