9
$\begingroup$

I've heard older hams talk about "aligning" their equipment. E.g. "I sent it to a guy for alignment" or "that rig probably needs to be completely aligned before you use it".

As a kid, sometimes I remember broadcast AM/FM receiver dial indicators would get "stuck" and you'd have to fuss with the knob, like crank it all the way one direction for a while, to get it to properly line up with the rough tuning labels again.

Is "alignment" basically that only on a more precise VFO indicator? Or does it involve more tuning elsewhere, say re-adjusting to factory biases via trimpots? Or is it not really a physical adjustment thing at all, more like checking capacitors or replacing tubes?

|improve this question
$\endgroup$
  • 1
    $\begingroup$ Great question, but your title could just as well say "What does it mean...", because alignment is necessary on newer equipment also. $\endgroup$ – Mike Waters♦ Apr 10 at 19:39
4
$\begingroup$

It's more complicated than that. One of the things you do in an alignment is like what you describe, making sure that all of the fixed and adjustable frequencies inside the rig are correct and agree with what's on the dials. This might involve mechanical or electrical adjustment. But in addition to that you do things like

  • Adjusting the tuned filters for different IF stages to make sure that they have the maximum response in the places where the signal ought to be
  • Adjusting band pre-select filters to make sure that they admit as much of the desired band as possible, with a minimum of everything else
  • Adjusting the gains and biases of various amplifiers so that they're operating in the ideal range, where they will pick up weak signals, but without saturating or distorting on strong signals
  • Making sure that the receive and transmit sides of a transceiver are in good agreement, and the RIT offset is really 0 when that knob is at 0.

If you have some time, I recommend this Mr. Carlson's Lab video for a pretty detailed rundown of aligning a receiver; a few of his other restorations involve similar tuning-up.

|improve this answer
$\endgroup$
4
$\begingroup$

The process of alignment involves optimizing the settings of variable inductors and/or trimmer capacitors in the set to maximize sensitivity and selectivity. It usually involves feeding the set a series of precise signals and adjusting particular components, in sequence, in each case to maximize output volume or voltage at a particular test point.

This was mostly a procedure of the vacuum tube era, though solid state sets (even pocket transistor radios) could also be aligned. Once set, however, only extreme conditions or a goodly number of years of operation (resulting, in either case, in value drift of components like capacitors and resistors) would generally require realignment. One exception to this is that replacing a tube in a vacuum tube set might change some value (dependent on the replaced tube) enough that realignment would be of value.

There are at least a couple YouTube videos that show the process (with a little compression, not to see all, in that case, 23 adjustments required) -- in one of them, the operator has to use an alternative alignment frequency to work around a very strong local AM broadcast station close to the recommended one.

|improve this answer
$\endgroup$
  • $\begingroup$ Ah, you beat me by 5 minutes! ;-) Nice answer, except that alignment is not limited to superhets. I have aligned many early-20th century TRF receivers as well. $\endgroup$ – Mike Waters♦ Apr 10 at 19:33
  • $\begingroup$ Even direct conversion SDR transceivers need alignment from time to time, since they also have components which age. $\endgroup$ – AndrejaKo Apr 11 at 10:33
  • $\begingroup$ Thanks -- on reconsideration, I agree, anything with carbon comp resistors or electrolytic capacitors may require realignment (transistors might well drift value over time as well). Edited to generalize. $\endgroup$ – Zeiss Ikon Apr 11 at 11:20
  • 1
    $\begingroup$ I can't think of a case where an out-of-spec electrolytic capacitor would be compensated for by realignment. They are seldom used to either couple or bypass RF. $\endgroup$ – Mike Waters♦ Apr 11 at 17:05
2
$\begingroup$

As Mr. Peabody would say in a cartoon of my youth, "Sherman, set the WABAC machine!"

As shown in this block diagram of a double-conversion superheterodyne receiver, the signal from the antenna would be heterodyned - mixed in modern parlance - down to successively lower intermediate frequencies:

enter image description here

A primary purpose for the conversion steps was that the achievable bandwidth for a given filter $Q$ becomes narrower as the cutoff frequency is decreased, improving selectivity, the ability to reject unwanted signals on adjacent frequencies. Triple-conversion "superhets" were not unknown and the more recent trend of up-converting the antenna frequency to ~70MHz before downconverting it twice for single-signal filtering has only recently been seriously challenged in ham gear.

Affordable bandpass filters in the 1st and 2nd IF stages were based on multisection LC resonators, around which an entire field of study arose. Regardless of whether the sections were tuned to the same frequency or were "stagger" tuned, inevitable component variations required that a laborious "alignment" process be followed to optimize receiver performance.

As single sideband, supressed-carrier modulation (SSB) supplanted AM, the superior performance of resonators based on piezoelectric and mechanical filters over LC phasing networks resulted in the dominance of the "filter method" of SSB generation. The great expense of these filters, in turn, was a driving force in the development of the "transceiver," which combined the transmitter and receiver into a single unit. This allowed the very high-$Q$ SSB generation filter(s) to be deployed in the receive chain. The elimination of multiple LC resonators in two receiver stages all but eliminated the need for the receiver "alignment" process.

|improve this answer
$\endgroup$
2
$\begingroup$

Alignment usually means to turn various built-in adjustable components to put the equipment back to factory specs. This is necessary because as some electronic components age, they change in value over time. That can and does cause reduced performance of the radio.

There are two basic types of alignment. This is kind of tongue-in-cheek, but bear with me. ;-)

  1. Adjusting the adjustable adjustments
  2. Adjusting the non-adjustable "adjustments".

The "adjustable adjustments" are built-in adjustable components, such as:

  • Trim pots (variable resistors)
  • Variable capacitors
  • Variable inductors

These are found on IF cans (containing transformers).

"Non-adjustable" adjustments are necessary when a component has drifted out of specs, and the technician must add a component in series or parallel with it. For example, I had to trim the BFO crystals in my Collins S-Line back to spec by adding a capacitor in parallel or in series with the crystal.

The mechanical adjustment of the pointer could also be considered as alignment as well, I suppose; but that's not what is usually meant. A blind person would likely not be affected by that.

There's more that could be said, but basically, that is what it means to align a radio. I have done this many times over the years.

|improve this answer
$\endgroup$
  • $\begingroup$ Although I have aligned my tube receivers at least twice since 1979, some components have aged again to the point where they are desperately in need of alignment again. One of them is a Collins 75S-3, which used mil-spec components such as dipped silver mica capacitors. $\endgroup$ – Mike Waters♦ Apr 10 at 19:51
  • 1
    $\begingroup$ Uh oh. I've heard of silver-mica disease. Much worse than component aging... $\endgroup$ – Zeiss Ikon Apr 11 at 11:24

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.