Aligning Superhet w/Output Meter?

[K4RT]

Has anyone used an "output meter" to align a superheterodyne receiver, and if so do you have any tips, suggestions, etc. in using one for this purpose? I know that alignment can be done without an output meter, but some of the literature I have such as old handbooks mentions using one during alignment, but no more than that.

Brad

[KA2DZT]

You can put an AC meter on the speaker terminals and use it to align.  Use an analog meter, DVM are useless for this purpose.

Fred

[Pete, WA2CWA]

Across the speaker leads a scope also works; even a low wattage/low voltage lamp. Adjust everything for maximum output.

[n1ps]

Another test point is to use the AVC voltage.  I like to use that at times with a scope or VTVM.

[K4RT]

Thank you for your thoughts. I recently picked up a Weston model 571 output meter.

Brad

[WBear2GCR]

sometimes the "S meter" will suffice.

The "marker" or "calibrator" can serve as a signal source.

It's not ideal, but probably will get most receivers "in the ballpark".

                  _-_-

[K5MIL]

Connect the ac meter, set to the most sensitive (lowest reading) scale, across the speaker terminals.  Turn the receiver volumn to maximum. Adjust the modulated signal generator level to the point that you just get an indication on the ac meter. As you peak the circuits, keep the signal generator level to the minimum necessary for an indication on the ac meter. This will keep any avc action from skewing the alignment peaks and the tone from blowing you ears out.

Bill

[MikeKE0ZUinkcmo]

A fair number of old manuals recommend using an output power meter and GR made what appears to be the most versatile one made.   Power ranges are from 2milli-Watts to 20 Watts full scale and load impedances range from 0.6 Ohms to 32K Ohms.

[N2DTS]

Maybe just what you want for a CW receiver, but a bad way to go for AM.

In the old days, they had sommething called a warbulator, sometimes it was a motor driven VFO that moved back and forth over a range, so you could adjust the IF cans for the best passband.

Now, nothing beats an sdr hooked up to the IF, you can see what each adjustment does and see the shape factor of the IF in real time.

[WB2CAU]

Maybe just what you want for a CW receiver, but a bad way to go for AM.

In the old days, they had sommething called a warbulator, sometimes it was a motor driven VFO that moved back and forth over a range, so you could adjust the IF cans for the best passband.

Now, nothing beats an sdr hooked up to the IF, you can see what each adjustment does and see the shape factor of the IF in real time.

Brett,

This sounds like a great idea, and I'd like to try this.  Maybe my brain is asleep and I'm missing something obvious here, but how are you coupling the very high output impedance of the last IF stage into the low impedance input (ie: 50 ohms) of the SDR receiver without loading down the IF, changing its characteristics, and still have enough signal to display on the panadaptor?  Am I over-thinking this?

Eric

[N2DTS]

Keep in mind, the IF is a high level signal compared to what comes in an antenna, so just get a probe close to the last IF can output is enough.

In my home brew receivers, I just put a 10 pf (or maybe less) cap on the IF that goes to a scope output so I can look at my and others modulation.
I have hooked the sdr-iq up to that and you can see the IF shape.

In my receivers, I have a filter right at the mixer output, and that does the filtering, the IF transformers are broad band units and do not really do anything, so the IF output looks like the mechanical filter plots.
In a receiver where the if cans are the filters, it pays to see what each adjustment does.

You can get the response to look like almost anything...

[MikeKE0ZUinkcmo]

Maybe just what you want for a CW receiver, but a bad way to go for AM.

Audio power meters were routinely used for aligning AM I.F. strips, as this excerpt from National's HRO-60 manual.

In the old days, they had something called a wobulator,

That was the GR 1025 Generator you're referring to I believe, and its still known as a sweep generator.

[N2DTS]

I think they used to look at it with an O scope to see the response.
I once saw a picture of a generator with a little motor built in, it had an arm that turned a knob back and forth.

[K4RT]

I have found a little more information about use of an output meter.  It seems that they were widely used by shops that serviced AM broadcast receivers back in the day, although output meters were not the only method used. Mike, that GR model is a nice unit.

Once I turn to the alignment of my National receiver, I'll try to remember to follow up here and post a note or two about how it works.

Brad