[HBR] Progess report and 50:1 drive idea

[N2EY at aol.com]

In a message dated 4/25/06 5:06:13 PM Eastern Daylight Time, 
waltah at earthlink.net writes:


> Bill said:
> > While 20:1 is not the 50:1 which is the subject here, it still
> > takes 12 feet to cover the 180 degrees...does that still make it
> > 20:1? 
> 
> I THINK so.   A sideband signal has to be tuned in within about 10-20 cps 
> to sound right, doesn't it?   Neglecting the allowance for end effects, 250 
> kcs spread over 25 revolutions to rotate a cap 180 degrees is 10 
> kcs/revolution or a bit less than 30 cps/degree.   It does depend somewhat 
> on the quality of your dial mechanism -- I can set the dial on an LM or BC-
> 221 much more precisely than a 6:1 planetary ball drive.   

The PW and NPW drives are ten turns to cover 500 divisions. 20:1 ratio, but 
only half a revolution is used. The divisions are spread out but they go by 
fast. 

The LM/BC-221 caps and the ARC-5 tx caps require fifty turns to go from end 
to end. 100:1, but only half used. Five times slower than a PW or NPW. 

> 
> Using a PW dial (12' scale length) gives you great ease of reading the dial 
> and correspondingly good resetability, to the limit of your ability to 
> accurately position it.  
> 

Yep. But when you are tuning, the kHz go by pretty fast.


> 20:1 would be ideal for an AM/CW receiver or for an SSB set with 100 kcs 
> bands.   For 250 kcs, I think 50:1 is better.
> 

For CW use I find 5 kc/turn to be the maximum I will put up with. Maybe 10 
kc/turn on a good day. But there's no reason to put up with fast rates when such 
good mechanisms are available and inexpensive. 

The first receiver I built with an ARC-5 dial was in 1972 or so. 6 kc/turn, 
sharp CW filter. Predecessor to the 'silver receiver' on the HBR site. Spoiled 
me rotten. 


> One check point:  I have a two-speed Jackson Bros. drive on the R8040A.   
> The 'fine' ratio is about 36:1 and those are 500 kcs bands -- 3500-4000 
> and 6800-7300, with very little extra.   The calibration isn't too close to 
> linear, so the ratio at the high C end (75 meters) could be around 20 or 
> 25:1.   That's too quick for me, even with a fairly large knob.
> 

Yup. 

There's a reason older receivers have such fast tuning rates: Hams back then 
operated differently. In the old days. it was common for hams to have only a 
few crystals, and to answer calls many kc. away. Even before crystal control, 
most self-controlled rigs weren't easy to QSY. 

Most QSOs then were "split" - the stations on two different frequencies. 
(This is where the traditions of long calls came from, too). To cover the band 
quickly, fast tuning rates and wide receivers were the norm.

This kind of operating developed around the available equipment. It was 
wasteful of spectrum because each QSO used twice as much of the band as would be 
needed if both stations used the same frequency.

The widespread use of VFOs and transceivers has changed things. No reason to 
operate like they did back when.

73 de Jim, N2EY