Setting up for alignment

Bottom front: Heathkit SB-600 speaker, HR-10 receiver. On speaker: Trio SG-401 signal generator. Rear Heathkit IM-5284 multimeter. Notice alignment tool behind the dial needle on the receiver!

I apologize for not using a Heathkit signal generator for this work. That would be most fitting. Especially the IG-5280 RF Oscillator that not only was a low cost entry level model, just like the receiver. It also uses the same case as the IM-5284 multimeter and they are stackable. In my defense, I found an SB-600 speaker for the occasion. Not bad?

I built the IM-5284 years ago for the purpose of aligning my SB-104A that I was building at the time. The rest of the 52xx series would be nice to have, but out of economic reach at the time.

I now have several digital multimeters. They are more accurate, more convenient, smaller and more versatile than the IM-5284. Most are autoranging and none use batteries as quickly as the IM-5284. Most of them are cheaper too. So I use them a lot. The old IM-5284 gets used when I need to measure current, especially for a long period as it can do so without batteries.

For peaking circuits, an analog meter beats the digital ones. There will be a lot of peaking when I align the HR-10. So the IM-5284 may get batteries for the first time in more than a decade. Besides, it’s a Heathkit so it has a VIP card when it comes to working on the HR-10.

BFO alignment

My strategy for getting the BFO frequency right is simple. Tune a carrier for max using AVC and the S-meter. Then with the front panel BFO tune in the 12 o’clock position, adjust the coil slug for zero beat. Using a Heathkit alignment tool of course.

Easy said. There was no well defined peak. The IF filters are rather broad, which makes sense for a AM receiver. Turns out the RF gain setting changes the Local Oscillator frequency dramatically. Also, at high RF gain settings the BFO does not appear to work properly. But I did my best. It was way off when I started. Now it seems to be quite ok. The proof of the pudding comes when listening to CW and SSB on 80, 40 and 20 meters. USB and LSB settings appear symmetrical. I could listen to qsos on all of those bands.

There was no amateur activity to be heard on 15 or 10 meters. But I could hear AM broadcast that was definitely not transmitting in those bands. This was probably a case of image or other spurious signals. Keep in mind that the local oscillator uses frequency doubling for these two bands, increasing the number of spurs. Better front end filters may help. Aligning them is next on the list. Or may be the IF filters first?

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