[ARC5] Drift in BC-453 - more

[Bob kb8tq]

Hi

If you are running a radio at 400 KHz, and a similar radio at 4,000 KHz the drift of the 
second one (in Hz) probably will be 10X the drift of the first radio. The same applies
if you go to 40 MHz (you now are at 100X vs 400 KHz). Yes, there are a bunch of 
assumptions there about radio construction, IF frequencies and various other things. 

To the extent this is “simple”, a 1 Hz drift on a BC-453 would be about the same as a 100 Hz 
drift on a similar radio on 10 meters or a 10 Hz drift on 80 meters. Simply put - if you *think*
you could listen to SSB on 10M with a low IF / single conversion non-crystal based
radio (ignoring anything but drift as a problem) … you should get about 1 Hz drift on the 453. 
You could compare to comfortably listening to SSB on 80 M as well. 

Of course, you immediately get into “drift over what period of time”. Any radio like this that I
ever used for SSB stayed on pretty much all the time. Use it in the evening and leave it on 
all day while I was busy with other stuff. Starting from dead cold … yikes …. that’s a tough
test for a tube based radio. 

If you *do* want to test for sub 1Hz sort of stability it’s likely easier to shove a stable signal 
into the radio and let a computer look at the audio coming out than to do a bunch of other 
crazy stuff. The advantage is that the result of the test is looking at the same thing the 
decoder software in the computer will be looking at.  There are a lot reasonably stable 
oscillators on the auction sites to provide an adequate signal. The risk is more spending 
$20 and getting a dead one than anything else. Pretty much anything called an OCXO 
should do the trick. 

Lots of fun 

Bob

> On Dec 12, 2017, at 2:57 PM, Kenneth G. Gordon <kgordon2006 at frontier.com> wrote:
> 
> On 12 Dec 2017 at 14:32, MICHAEL ST ANGELO wrote:
> 
>> Bill,
>> 
>> What is this millihertz spec for WSPR? I haven't tried it yet but I
>> thought frequexcy stavility has to be a couple of hertz for the 2
>> minute cycle: 
>> 
>> <https://groups.google.com/forum/#!topic/2-meter-wspr/-hDK071K1iM>
>> 
>> Mike N2MS
> 
> Hi again, Mike. That spec is for 2 meters: it becomes far, far more critical at HF and MF. 
> Yes. Millhertz.
> 
> Since, "Many WSJT-X capabilities depend on signal-detection bandwidths no more than a 
> few Hz. Frequency accuracy and stability are therefore unusually important."
> 
> See this for details:
> 
> http://www.physics.princeton.edu/pulsar/K1JT/wsjtx-doc/wsjtx-main-1.8.0.html#GENERAL
> 
> In fact, someone on one of our lists mentioned something like <0.5 Hz drift in 2 minutes or 
> less. I can't remember the details now, but his post included the link above. As I remember 
> it, he also told us that if the drift exceeded what I mentioned above, that would prevent 
> decoding of the input.
> 
> I know that Bill Cromwell noted enough drift from the very slight drift in filament voltage by 
> line-voltage drift to cause very noticable drift. As he says, he decided to simply forego 
> attempts to use those modes.
> 
> Although I am inclined to agree with him, I am very curious to learn if it IS possible to use a 
> BC-453 for these modes. I would guess not, but stranger things have happened.
> 
> Ken W7EKB
> 
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