[Milsurplus] BC-9: NETTED! WoooHOOO!

[Bill Cromwell]

Hi Hue,

Those nets must have sounded like most of the hams in a CW contest these 
days. Most of the stations are clearly not zeroed on the calling 
station. It is even apparent in many of the traffic nets (yes there are 
still NTS traffic nets). The two most important things in ham CW is to 
not go outside the band, and more critically to not go outside the other 
station's receiving passband. Ideally the two (or more) radiated 
carriers would be on exactly the same frequency (*zero* beat). But that 
degree is 'fussy' isn't actually needed.

I have a SSB transceiver here that does CW but has only a SSB bandwidth 
filter (~2.7kc). In CW mode the carrier oscillator is shifted to give 
slightly more than 600 cycle offset. A lot of CW signals will fit into 
that space. An Audio filter that is carefully measured to give the same 
peak response as the offset can help get the rig 'netted'. I usually use 
a digital filter (DSP) running on my computer (but an op-amp or tube 
based 'select-o-ject' will do). With the computer I get a spectrograph 
on screen similar to a 'panadapter'. The scale on that display is in 
cycles per second with zero (the BFO/carrier) at the left side. The 
incoming signal in my case is then tuned to the 600 Hz (The known 
offset) marker on screen and I am 'netted'. The actual target is 620 
cps. The parts that give the offset are fixed and it is fussy work 
changing them. A variable cap in that location is not reachable for 
tweaking while the radio is assembled and in operation. 620 is close 
enough to my favorite of 650. This approach might help Dave get his rig 
setup where he wants it. This approach also helps (faster/easier) with 
netting using separate rx/tx gear. By the way..the sound card gear also 
works with regens and DC receivers. Pulling of the receive 'local 
oscillator' will still be a problem with separates (regen/DC) but when 
Dave knows the offset in his transceiver it will work for him. And the 
DSP filtering will help on contest weekends :)

73,

Bill  KU8H

On 02/20/2017 02:14 AM, Hubert Miller wrote:
> So are you saying there should be an optimum, design offset?    It sounds to me from the manual, where it explains the compensating C6, that maybe the goal was
> no offset?  Receive = transmit frequency ?
> If there is an offset, by design or by the variability of circuit components and battery state, i suggest that operators were maybe cautioned to all use only the
> upper beat note ( "LSB" HFO ) and to choose a beat note well under 1 kHz. To minimize stations chasing each other across the band.
> As there's no real zero-beat capability, since you can't zero-beat the transmitter against the other station, the net must have been interesting to listen to, with
> stations spread around a narrow range.
> -H
>

-- 
bark less - wag more