[ARC5] ARC5 CW Question

[Mike Hanz]

Excellent question.  If you want to *short* the back emf, yes.  
Unfortunately, circulating the energy in the collapsing magnetic field 
back through the coil also significantly lengthens the time the relay 
hangs in there after turning off the power.  That's not a good thing for 
a keyer...unless you enjoy sending at 5 WPM or less...:-)   You have the 
same problem with using a capacitor across the coil.  By using a 
*series* diode on *each* coil, you prevent that energy from feeding back 
into the other coil and thus keeping it alive for a longer period...and 
vice versa.  If you put a scope across the key, you'll see a fast pulse 
of a few microseconds across it - the current has no place to go, so the 
field in each relay collapses very quickly.

  - Mike

On 6/22/2014 2:42 PM, Jay Coward via ARC5 wrote:
> I always thought you put the diode across the coil to short the back emf. (?)
> Jay
>   
> -----Original Message-----
> From: Mike Hanz <aaf-radio-1 at aafradio.org>
> To: J Mcvey <ac2eu at yahoo.com>; ARC-5 List <arc5 at mailman.qth.net>
> Sent: Sun, Jun 22, 2014 11:33 am
>
> On 6/22/2014 11:12 AM, J Mcvey via ARC5 wrote:
>> In summary, the only relays that should be clacking when keying is the antenna relay in the BC442 antenna switch unit and K52 in the MD7. Is this correct?
>>
> That is correct.  Steve KB4DMF discovered the chirp described in my
> first e-mail after putting together an entire two transmitter/three
> receiver set in its original complete form.  That's not typically how
> hams used/use them, so we had never heard of any anomaly like that
> before.  Ferreting out the reasons behind the chirp and fixing it was an
> interesting exercise.