[ARC5] BC-221 and LM on eBay

[MICHAEL ST ANGELO]

Thanks. realistically his is fine for AM but not CW (nor SSB but it was not designed for this mode).

Mike N2MS

> On 03/28/2022 12:23 PM Bob kb8tq <kb8tq at n1k.org> wrote:
> 
>  
> Hi
> 
> The answer is very much a “that depends” sort of thing.
> 
> The internal crystal isn’t temperature compensated. If you zero it today indoors
> and use it outdoors a month from now, there will be an error. If you let it warm
> up / stabilize for a couple days, zero it, and then use it … maybe not much error 
> from the crystal.
> 
> A lot of stuff with one of these depends on zero beats. Just how close you can 
> get on a zero beat depends on multiple things. How good are your headphones?
> Do they go deaf at 200 Hz? Can you still hear a rumble at 20 Hz? Are the levels
> such that you can get a “swish swish swish” sort of beat note well below the
> audio? How close can you guess between the two sides of a 20Hz beat note? 
> 
> First step is to sync the crystal to WWV. 20 Hz is a reasonable thing. Fractions of a 
> Hz are not at all easy. Is you lab temperature stable enough / your crystal good enough 
> for that to matter? Maybe it is … maybe ….(yes, this is *lots* easier with a BC-221 that 
> lets you easily get to the crystal tune cap from the outside ….). 
> 
> What WWV-ish thing are you checking against? 20 Hz at 5 MHz is 4 ppm. At 20 MHz
> it would be 1 ppm. All the transmissions are equally accurate so higher (if you can 
> hear it) is going to be “better” in this case. 
> 
> If you are at a zero beat “cal point” you are right back to how close that zero beat is.
> Since the cal points are harmonics of this vs harmonics of that, the math of how close
> 20 Hz is a bit harder to work out.  ( Yes there are “unlisted” cal points that can be 
> used, that gets really crazy really fast).
> 
> With your 4 MHz signal, is that a transmitted signal or a received signal? You may
> have yet another “how close can you zero beat?” tossed into the mix. 
> 
> Does this all add up to <5 ppm accuracy? Probably not, though it might. Something 
> closer to 10 or 20 ppm is likely the practical limit once rest of the mechanism gets 
> into the act. Again, this is in a bench environment with a lot of care being used. 
> 
> Bob
> 
> > On Mar 28, 2022, at 10:24 AM, MICHAEL ST ANGELO <mstangelo at comcast.net> wrote:
> > 
> > I picked up a BC-221 and a neighbor gave me a LM frequency meter. He was a high school physics teacher and one of his students gave it to him.
> > 
> > What is the published frequency accuracy of these meters? The only notes I could find online is this observation by VE3BDB. He read in the manual that that the maximum error will occur when measuring a 4 MHz signal at minus 30 degrees C where an error of 1.355 KHz (0.034%) could occur. His observations indicated that the BC-221 is easily capable of 250 Hz accuracy on 80 & 40 M.
> > 
> > <https://www.qsl.net/ve3bdb/bc221observations.htm>
> > 
> > Mike N2MS
> > 
> > 
> >> On 03/28/2022 8:38 AM Bob kb8tq <kb8tq at n1k.org> wrote:
> >> 
> >> 
> >> Hi
> >> 
> >> As an “all in one” gizmo for keeping a pile of HF radio gear tuned up,
> >> I still would put the LM / BC-221 pretty close to the top of the list. Yes,
> >> there would be other things on the list as well. With care, you can do a 
> >> lot of things with one of them.
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