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Actuay it does drive 4 ohm speakers at lower operating voltage.? However at 12V you really want 32 ohm.

THe spec has 4.5V for 4ohm, 6V 8ohm, and 9V 32ohm as minimums.

Its why I put a regulator in mine to dial it down to 8V.? Less issues.

Allison

You can't just connect D4 and D5 to the SDA/SCL leads.

You need an I2C adapter added to the back of the lcd.

this is an example:

www.ebay.com/itm/Serial-IIC-I2C-Adapter-1602-1604-2002-LCD-Backpack-Arduino-FAST-SHIP-US-SELLER/171036006949?hash=item27d28a5a25:g:vNIAAOSwMmBVnc7K:sc:USPSFirstClass!66609!US!-1

It is the audio amp in the Ver 4 board, Q72/Q73, Q71 in the following:



Basically it looks like a little push/pull class AB amp consisting of a 2N3904, 2N3906, with a 2N3904 driver, but I don't have much experience with this circuit as all my audio amps have either been vacuum tube or some type of chip amp.

So, will this amp get damaged by a 16 ohm speaker?? Would it put out 1/4 to 1/2 watt or more?? Later today I hope to try it out but didn't want to fry anything.? I'm going to keep the bitx box itself very simple, just adding a small internal speaker that will work when nothing is plugged into the headphones jack for casual monitoring.? I guess I could add a small board with a LM386 easily, but that would draw more current when I operate from battery and add complexity inside the radio.? Any of the small class D chips might add noise inside the radio.

Now gear from the 20s or spark gaps - you're on your own there :)

I don't have much experience around RF design.
So take my opinion with a large grain of salt.
But here goes anyways.


On 15 meters, the spur is only 3mhz away: 45mhz-21mhz= 24mhz
That's a fairly of sharp filter for implementing in L's and C's.

There is an easy solution: don't drive the mixers with too much mike audio.
The only difficult part is determining what is too much mike audio, but
that is solvable.
/g/BITX20/message/51211
Adding that extra gain stage may be a good idea anyway, as it may make
it easier to get a consistent 10 Watts from the final. We can leave
some of the
2n3904's in place and reduce the gain per stage to 10dB.

As Howard points out, the rules (at least here in the USA) are fairly
lax below 30mhz,
We are compliant with current rules if we keep that mike audio in check
when operating at 21mhz and above.
And even if we screw up, we're still likely doing better than somebody
running some old gear from 1970.
Especially if our power level is only 10 Watts.
/g/BITX20/message/51270
/g/BITX20/message/51264

If running the uBitx into a 100 Watt linear at 21mhz and above,
I would measure the spur to make certain it was compliant.

Of course, adding filters can be a good thing, especially on 10 meters where
the spur is far from the operating frequency.
I would probably just put a bandpass filter in line with the antenna coax.

I'm surprised those mag-loop guys haven't chimed in here yet.
Would be perfect for filtering the spur when operating on 15 meters.

Jerry, KE7ER



On Tue, Jun 5, 2018 at 07:31 am, ajparent1/KB1GMX wrote:

The good news is there are enough control signals to select either 2
or 4 band filters.
Where to put them and also add gain to make up for insertion loss
are issues.

If only one band its easy. The filter and detect that no other than
30mhz low pass is selected.
That takes a transistor and a relay. And a band pass filter for 10
or 15M, pick one.
Still needs more gain to get power out on 10M then. A MMIC with
10-12db gain good
for +5 dbm or more would do fine.