[GreenKeys] Range Finder Setting/Distortion usage?

[W2HX]

Ok guys. So here is my next question about this. Could there be a detrimental affect of the bias supply is not of the same polarity of the external supply? I ask because recently I made a new jackfield for my loop. And on everyone's suggestion I made the "tip" positive. In the past, I don't think it was. So I am wondering if I might be reducing the effect of the bias windings on the relay if the main winding from the external loop changed polarity?


73 Eugene W2HX
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-----Original Message-----
From: greenkeys-bounces at mailman.qth.net <greenkeys-bounces at mailman.qth.net> On Behalf Of Harold Hallikainen via GreenKeys
Sent: Sunday, February 5, 2023 9:48 PM
To: greenkeys at mailman.qth.net
Subject: Re: [GreenKeys] Range Finder Setting/Distortion usage?



On Sun, February 5, 2023 7:32 pm, Jim Cooper wrote:
> On 6 Feb 2023 at 1:56, W2HX wrote:
>
>>
>> I wonder... the ASR (which seems
>> less accurate than the KSR) has an
>> internal loop supply and relay to
>> key the page printer. This relay also has a bias adjustment. I have 
>> that adjustment at 30mA as per some notes from the guy I bought it 
>> from. Could this bias current in the ASR play a part in these two 
>> machines behaving slightly differently? If so, then I can play around 
>> with adjusting the bias current on the ASR (I guess I could play with 
>> it regardless, but thought I'd get the skinny from the experts who 
>> know.
>
> That could definitely explain the 'skew' to the higher numbers ...  
> imo
>
> w2jc
>

I agree. I've always wondered why a polar relay is used if a polar line is not being used. It seems to add more complexity and more things to go wrong. MAYBE the polar relay and internal loop supply can be bypassed and just have the loop and terminal unit drive the selector magnets directly.
Failing that, I'd try to adjust the polar relay such that there is no bias coming out of it. If possible to sample the loop current after the polar relay, then adjust the polar relay so both mark and space on RY are 22 ms long. Ideally a test signal would be available with a 22 ms stop bit instead of the usual 31 ms. That makes it easier to see on a scope since every bit is the same length. Also, if all alternating bits are the same length, the average current on a slow moving meter would be 30 mA.
However, since there are 5 data bits, start is space, and stop is mark, even with a 22 ms stop bit, getting a 50% duty cycle with an R or Y is not possible. I did create some audio with random 22 ms bits at https://w6iwi.org/rtty/audio/ for DSP TU testing (generating the eye diagrams at https://w6iwi.org/rtty/DspTU/ .

In general, I think the ideal design has zero parts, and a polar relay that is not converting a polar circuit to a neutral circuit is not heading us towards the ideal design.

Good luck!

Harold
https://w6iwi.org

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