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 Post subject: Correct tuning of CW stations with R390a
PostPosted: Nov Thu 19, 2020 2:45 am 
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Joined: Mar Fri 29, 2013 4:46 am
Posts: 216
Location: Livermore, CA
What's the correct way to tune in a CW station with an r390a. As I tune through the station there's a peak then a zero beat then another peak. Is it best to set the BFO at midpoint tune for zero beat then adjust BFO towards the + side for 600-700hz pitch?

Dave


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 Post subject: Re: Correct tuning of CW stations with R390a
PostPosted: Nov Thu 19, 2020 4:13 am 
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Joined: Jun Wed 13, 2007 4:53 pm
Posts: 232
You should tune for maximum signal with the narrowest filter (0.1 Kc). Then tune the BFO for the desired beat note. If the radio is aligned correctly, setting the BFO to 0 should give you zero beat at the same frequency as maximum signal with the 0.1 Kc bandwidth.

Ed W2EMN


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 Post subject: Re: Correct tuning of CW stations with R390a
PostPosted: Nov Thu 19, 2020 5:53 am 
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Joined: Mar Fri 29, 2013 4:46 am
Posts: 216
Location: Livermore, CA
djed wrote:
You should tune for maximum signal with the narrowest filter (0.1 Kc). Then tune the BFO for the desired beat note. If the radio is aligned correctly, setting the BFO to 0 should give you zero beat at the same frequency as maximum signal with the 0.1 Kc bandwidth.

Ed W2EMN

Okay that's exactly what's happening tuned for max signal .1kc bandwidth, turned BFO to "0" position signal was at zero beat.


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 Post subject: Re: Correct tuning of CW stations with R390a
PostPosted: Nov Thu 19, 2020 2:36 pm 
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Joined: Jun Mon 24, 2013 3:00 pm
Posts: 1695
Location: Champaign IL 61822
That's after the set is warmed up. Just yesterday I check the warmup drift of mine.
Its great for a boatanchor, both the PTO and BFO drifting about 600 Hz from
cold start to four hours warmup. But at the start, biggest signal at the 0.1 kHz filter
position and centered BFO produces about a 600 Hz beat.

Is this typical for an R390A?


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 Post subject: Re: Correct tuning of CW stations with R390a
PostPosted: Nov Sun 22, 2020 12:59 am 
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Joined: Jun Wed 13, 2007 4:53 pm
Posts: 232
A little hard to imagine that the BFO would have a warmup drift of 600 Hz, at least when new. But things can change over the 60 years most of these radios have survived. Moreover, most of these were operated 24/7 and so warmup was not an issue. I don't think I ever saw a requirement on warmup drift in the MIL-SPECs. Reading one of the other threads, some have replaced the temperature compensating caps in the BFO and have gotten the warmup drift to around 100 Hz.
Still pretty impressive compared to the WW2 radios like the Hammarlund Super Pro (which was actually a 1935 radio). I spent time trying to correct a warmup drift of 60 KHz at 15 MHz. Even after a couple of hours warmup it would drift a few KHz. No wonder they had full time radio operators back in those days.

Ed W2EMN


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