[ARC5] Drift in BC-453 - more

[Bob kb8tq]

Hi

You *will* notice 5 Hz a minute on SSB. Most people will notice 5 Hz / 10 minutes if the QSO goes on for a while. You also will get a bit bothered by it on 170 Hz shift RTTY if pictures or something similar is being sent. Net operation is yet another place you will notice it. PSK modes tend to be bothered by a few Hz of shift, simply because of the narrow bandwidth. That puts pretty much all of them in the category as well.

Indeed a straight tube radio with no crystals involved will require some tuning to stay “on channel” for SSB. How much depends on 80M (not a whole lot) vs 10M (quite a bit). Both are normal HF bands that people run SSB on. 

Back in the day, the BC-453 was commonly used by a lot of us as a tack on “super IF” for various radios. I don’t ever remember it being an issue for drift compared to the radio that was feeding it. Simply put, the drift came from the 4 MHz -> 455 KHz process, not from the 455 -> 85 KHz conversion. 

The debate seems to be 5 Hz per minute vs 5 uHz (or 5 mHz … ) per minute as the requirement for HF WSPR.

Bob


> On Dec 16, 2017, at 6:24 PM, J Mcvey via ARC5 <arc5 at mailman.qth.net> wrote:
> 
> Neil,
> 
> Yup!
> I did mention 5Hz/minute.
> The radio works fine for CW because the drift is almost imperceptible to the human ear , but WSPR notices! 
> 
> I guess you haven't worked with waterfalls and these digital modes?
> The issue is obvious.
> This stuff requires a whole other level of timing and stability.
> I also said that I will do a an actual analysis when time permits...
> 
> My hope was that someone other than myself is attempting to get a command set to receive  WSPR and JTXX modes.
> Anybody?
> 
> 
> 
> 
> On Saturday, December 16, 2017 5:53 PM, AKLDGUY . <neilb0627 at gmail.com> wrote:
> 
> 
> The thread has meandered around because we haven't been given anything to go on.
> You have blamed the BFO but haven't mentioned any stability figure.
> 
> Is the B+ feed to the BFO tube original? Are the resistors good? Have they been
> replaced by significantly different values? Is the decoupling to it still present? Are the
> caps bad?
> 
> Sounds silly, but has a 6SR7 been fitted yet the heater line been rewired for 12V? Are
> you running 25V on the heater line and a wiring mistake has resulted in 25V on the
> 12SR7?
> 
> I hope you've eliminated the painfully obvious.
> 
> Neil ZL1ANM
> 
> 
> On Sun, Dec 17, 2017 at 3:50 AM, J Mcvey via ARC5 <arc5 at mailman.qth.net <mailto:arc5 at mailman.qth.net>> wrote:
> This thread has taken many meandering twists and turns.
> It all started when I suggested that BFO stability may be the reason that WSPR cannot be decoded with a commend reciever.
> Yes, it is a "hobby thing" where I aspire to make a complete 630 meter station from command components.
> One of the "Ham-mered' transmitters can be re purposed as the transmitter and the BC-453 as the receiver.
> The transmitter will be controlled by XCO or VCO with PLL.
> 
> The computer systems drift ARE NOT the issue with WSPR. It works fine with other rigs.
> The BC453 LO "seems" to be stable if I leave it on a weak beacon station for a period of time.
> 
> I built a 85 Khz fet Colpitts oscillator from some junk box components. I hope it will be more stable than the command set BFO, but 
> it may have more phase jitter than I want.  We'll see...
> It will be used to drive the grid of the existing BFO oscillator disconnected from the set's BFO can. The plate circuit will remain intact .
> 
> I haven't had time to do  the drift measurements on the BFO and LO yet, but I will get there eventually. Stay tuned...
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