Hi Mark,

I laid out and folded a case of steel for my ubitx. Looking from the
front, my antenna connector is at the far right rear corner and the
internal connector wire is less than two inches long to reach from
the board with just a little slack. The DC power connector is over at
the far left back. The volume control is way over on the lower right
corner of the front panel along with the on-off switch. I routed the
power wires under the ubitx board to take advantage of the mostly
ground plane board to help shield it from RF at the finals, output
filters, and antenna connector. The power line runs much closer to
the front of the radio until it gets to the left side and then back.
It only comes out from under the circuit board *AT* the back corner.
There is no problem with RF. I hope this is helpful to you and others
when they layout and assemble theirs.

On 06/29/2018 01:17 PM, Mark M wrote:

The issue discussed in the 'RFI from uBitx TX after AGC and other
mods installed' thread appears to be caused by RF getting into the
12v supply and from there into the 5v supply that feeds the AGC
board (the ND6T/K5BCQ kit). At least that appears to be the issue
on mine. I thought I'd start another thread to talk about that.

I have the ubitx in a case from amateurradiokits.in. The power
comes in thru a plug in the rear panel at the right of the panel
(looking at it from the front), thru a fuse and then thru three
wires twisted together along the rear panel to the connector on the
board at the far left. There's also a polarity protect diode across
the supply. The power connector is right next to the antenna
connector and the supply wires run past the final transistors and .

I'm running the ubitx on 13.8v from an Astron 20A power supply, The
testing was done feeding a Heathkit Cantenna dummy load.

So, any suggestions on how to fix this would be appreciated. Don
mentioned heavier supply wires and capacitor at the input. I
thought I'd try re-routing the supply wires inside case to get them
away from the RF section. Moving the power connector to the other
end of the rear panel would make the run much shorter. Other than
that, I don't know. RF hardware is not my forte (I'm mostly a
software guy).

Thanks.... Mark AA7TA

You misunderstand me, Ralph. I don't WANT it to act the same. If I
wanted that, I'd just run it directly from the jump box. But I don't
want it to run away in RF, as at that level it can damage my tuner. I
want it to run at 5-10 watts, not 18-20! I can control it with the
amperage, and since the fuse is a 2A inline, I don't want it to run
more than that. So I'm certainly not going to set it to 3A unless I
want to toast marshmallows on my tuner.

开云体育

What if we use three diodes instead?

On Fri, 29 Jun 2018, 13:35 Raj vu2zap, <rajendrakumargg@...>
wrote:

Got back to town and plugged in the uBitxr4 and found the audio
distorted.

Poking around the finals I found that the two diodes D15 and D16
gave only a drop of 1.2V total
but the final transistors needed more like 1.5V. i.e. 0.75v each.

I simply cut the track between D5 and D16 and soldered a 100 ohms
multiturn preset as shown
in picture below. (Preset leads used is center and one side)

Start with the two soldered connections of the preset set to ZERO
ohms.

Power on and tune to a station at low volume and slowly increase the
preset till the audio
becomes clear. In my board the RX power consumption increased by
25mA at the best sound.
Just check and see that the output transistors are not getting hot.

My board sounded great with 47 Ohms between D15 D16 and I run at
13.6V. If you run at the
same supply voltage then you can try a fixed resistor. For 12V
supply you could try a higher value
like 56/62 or even 68 Ohms.

Cheers

--
Raj, vu2zap
Bengaluru, South India.

[image: Emacs!]

I confirm my 2A was not enough and shut down. Use at least a real 3A, linear is better to avoid any issue you might not even a clue.