Receiver Alignment - art or science?

[Ed/KB1HYS]

I aligned a toob type BC receiver.  I think I've done a good job, but maybe there's a better way...

I used a new SW receiver with a digital dial, to listen to the local oscillator, calibrated from the WWV.  Then I dialed in the LO and the dial ends etc by setting the new receiver to the Oscillator frequency (input +/- 455 kc) depending on the band) with the BFO on and zero beating the LO in the old receiver to that.

Then I used the scope and a signal generator at 455 kc to peak up the IF Cans.  I like this, doesn't require the set to be turned on and it's pretty easy to see where the peak is.

Still some more work to do, gotta replace a weak IF tube, and one of the IF cans has a bad trimmer. Luckily they are the large 4 inch tall jobs. Easy to open up and see what's going on in there.  Hopefully I can patch up the trimmer or whatever is wrong.

Still, I was able to listen to the Peoples Republic of China's SW station in Beijing tonight by bypassing the bad can & tube.  Sounded sweet, fading and all.

[The Slab Bacon]

Probably a little of both!!

Most BC type receivers are pretty simple. Use a sig gen and peak up the IF canz first, then check the dial tracking and tweak up the LO next to get the dial tracking as close as possaroo. Always remenber when tweaking up the LO to adjust the slug at the low end of the band and the padder cap at the top of the band. After tweaking up the LO, then adjust the RF amp / preselector coils the same way - slug at the low end, padder at the top end.
If you cant get the dial tracking right, be sure that you are tuning it for the right side LO injection. (If you find that you have had to adjust the LO adjustments more than a little bit, you are prolly tuning it for the wrong side injection)

Many communications receivers (and some BC rigs as well) have some wierd quirks in their alignment procedures, so it is always best to read the alignment procedure first. Some have have special requirements for bandwidth skirt shaping and / or proper AVC action.

Many times after learning that rig well, you may also find a few "shortcuts" you can take.

 

[KM1H]

In many areas, Southern NH included, you dont even need any test equipment to align a BC band radio. Use low and high end stations to set the oscillator band edges and peak the IF on a weak station. Dont expect overall calibration to be good, they werent built that way.

[K5UJ]

To learn about superhet design and practice restoration, I have been fixing up some vintage AA5 bc band receivers, well actually, only one so far, but it has been a real good experience in trouble shooting, restoration, and learning about receivers and I have come away realizing what an art there is to receiver design and why some hams seem to be more interested in receivers than transmitters (which I did not understand much before).  My first and only project so far has been successful:  I hauled out an old Admiral 5 octal tube rx from the early 50s and recapped it and changed some w.w. resistors, most important the one that smooths the ripple from the 1/2 wave rectifier tube, added some bypass caps around a grid resistor in the audio tube, plus a few other little things.  It sounds great now and with the wx lousy I am getting a surprising amount of enjoyment just listening to local bc stations on it because of the great tube audio from the almost 20 KHz passband.   I run it on a variac at around 100 v.   

[KG6UTS]

I aligned a toob type BC receiver.  I think I've done a good job, but maybe there's a better way...
......... I used the scope and a signal generator at 455 kc to peak up the IF Cans.  I like this, doesn't require the set to be turned on and it's pretty easy to see where the peak is.

 Sounded sweet, fading and all.

Hello Ed...from Ed

I do something very similar with a sig gen, scope or RF volt meter. I also use a digital RX as a reference and have access to some nice test equipment at work as well as my own heap at home. Sometimes it seems like working on cheap sets, AA5, and low end 'kid/novice' ham receivers can be as much or more of a challenge than the GOOD radios because of design shortcuts to save bux. Kind of as a side line in the hobby I've picked up a lot of vintage test equipment. Not sure if it is real or not, no scientific study ~8^o, but some times the values given in old alignment procedures could be allowing for loading from period test equipment.


EdZ XE2/KG6UTS
Loreto, Baja Sur .....annoying the fish

[Opcom]

It's a science, but may seem like magic from time to time.

[David, K3TUE]

It's a science, but may seem like magic from time to time.

Clarke's Three Laws:
[...]
3. Any sufficiently advanced technology is indistinguishable from magic.