Ge group--

Already ordered! 😃 thanks!

Jim:

Hi Marc,

Dave, NM0S, developed the new keying circuit.
The manual has a scope grab of the keyed waveform at the ARRL Lab testing standard of about 60 wpm (a skosh fast for the BJ's onboard key LOL)

On the Tx schematic, Q7, R21, D5, R22, and C34 form the keying circuit.
<http://www.4sqrp.com/kits/bayou%20jumper/Bayou_Jumper_revD_TX_Schematic.pdf>

The RC time constants of R21/C34 and R22/C34 help to soften the rise/fall of the RF envelope.
Q7 is in series with the 12V supply to both the oscillator Q5 and the PA Q4.
When the key is pressed, grounding the key line, C34 discharges through R22, slowing the turn-on of Q7.
When the key is released C34 charges through D5 and R21, slowing the turn-off of Q7.
The kit includes an extra capacitor (0.22 uF) that can be substituted for the 0.1 uF cap at C34 to soften the envelope even more should the builder wish.

One consequence of this scheme is that now crystal oscillator Q5 is no longer receiving supply voltage in the Rx mode.
So pressing the key while in Rx does nothing. That's one of the reasons we added the Crystal Spotter provisions under the top panel.

Jim, N5IB

Hi again Marc,

To address your other comment.... it would take a fair bit of cobbling and trace cutting/jumpering to implement the new keying scheme on earlier BJ versions.

In my estimation it wouldn't be worth the effort.
At hand-keying speeds (not 60 wpm - hi), at the ~5 W power level of the BJ, with the limited operating time most BJs see, any key clicks that are present are hardly going to drive other ops screaming from the bands LOL The keying sidebands are already down about 36 dB from the 5W carrier. That's 6 S-units below a QRP signal in the 40m band noise. If anyone more than spitting distance from my QTH could actually hear them, I'd mail them a QSL !

Jim, N5IB

Is it possible to put a Rev D board under a top board of another BJ? That is a blue top over a red bottom board?

Bob
KG5GTE

Hi Bob,

The dimensions of the Hobby Lobby box changed slightly a while back.
In response to that the boards for the revC and revD were reduced slightly (0.05") in length and width, and the mounting holes were moved inward a smidgen (0.025").

So, you can mix and match boards from revC and revD. (both red)

And you can mix and match revA and revB. (green and blue)

But to marry a revA or revB board with a revC or revD you'd probably have to hog out some holes a bit.
So your blue top panel from revB with a main board from revD would take a little cobbling.
When you enlarge holes you'll damage the though-plating on the hole's sidewalls, so you have to take care to see that the ground path between panel and main board is maintained.

RevA boards were the first to have the BNC connector repositioned and rotated 45 degrees, so you can't pair an original (white panel) board with any of the later versions.
Note that all of the main boards after the original (black) are green masked. It's only the top panels that have the other colors.

Jim, N5IB

Jim:
  Thanks for the very detailed explanation of the changes
to the keying circuit. I finally compared the schematics
of both the old keying circuit and the new. The
differences are very significant.
  I guess that it is definitely not worth it to change the old keying circuit for the reasons you noted.
Thanks again for this great kit!

72,

Marc. N4DR