[ARC5] Backwave

[Bill Cromwell]

Hi Rich,

I have seen the info about tweaking relay contacts for other radios, 
too. That is one means of "sequential" keying. The oscillator will be 
turned on first, followed by the antenna and then the buffers and 
finals. Going the other way, is just the reverse. The timing is in the 
low milliseconds to higher microseconds. It can be implemented with all 
tube technology (see Johnson Ranger and Heathkit Apache and probably 
more) or with solid state (or hybrid) approaches. I invite you to put 
"sequential keying" into your search engine or look in the indexes to 
your handbooks (if you have them). The transmitters under discussion 
might have to be modified for grid-block keying but that is the best 
solution.

I am thinking of adding one wire to my receivers to reduce or remove B+ 
from the RF and IF amps via that screen divider resistor stack so that 
the receiver can monitor the transmitter in place of a separate 
sidetone. That works best for me when using separates. It would be 
easily reversed when a museum piece is needed. Mine are not museum 
quality anyway and weren't when I got them.

For new construction I like the heterodyne VFOs.  A crystal oscillator 
and VFO run all the time (far from the operating frequency AND antenna) 
and the mixer that puts the signal on frequency is keyed with the 
transmitter. No chirp, yoop, droop, or backwave. That means you won't be 
using the built-in VFO and defeats part of the atmospehere using that 
transmitter in the first place. So many choices make.

73,

Bill  KU8H



On 10/26/2015 12:14 PM, Rich Post wrote:
> My thanks to Bill KU8H for summarizing the comments thus far.  I 
> certainly did not intend to start such a far-ranging discussion.  I am 
> VERY aware of the original purpose of the selector relay but had read 
> of success in using it for keying by simply bending its contacts 
> slightly so the oscillator is powered first so that chirp is 
> minimized.   That is not an option since the relays were excised long 
> ago according to the usual ham modifications in both CQ and QST.
>
> Bill, the distance was over 100 miles and the power supply was only 
> 155 volts for all three feeds; plates, screens and oscillator.  QRP 
> worked well.   Obviously band conditions were excellent so that even 
> the micro or milliwatt backwave signal was heard at that distance.  I 
> am looking for a solution not just for the backwave but for a 
> non-invasive break-in keying that includes the oscillator B+ as could 
> have been done with the now-missing selector relay.  I was thinking 
> possibly of using an opto-isolator and a high voltage N-channel MOSFET 
> or high volt NPN and also a mechanical relay for the PA cathodes given 
> the slight millisecond or so difference between the electronic "relay" 
> for the oscillator and the mechanical one for the cathodes. Was 
> wondering if anyone had experience with such a solution.
>
> Also working on a QRO capability with a Heath HP-20.  Am using a 
> hi-volt N-channel MOSFET and zeners on the 300+ volt line inside that 
> supply to freeze that to about 270 for screens and then to a resistor 
> for the 200 or so for the oscillator but there is also significant 
> backwave with that.
>
> Tnx de Rich KB8TAD