How you propose to control the drive to be of 5 watts on all bands for your 70 W amplifier

As the uBITX is giving much more power out put on lower bands? than on the higher bands

Satish

Virus-free.

On Fri, Apr 20, 2018 at 5:07 AM, Howard Fidel <sonic1@...> wrote:

Actually, I would prefer to rewind the transformer with a center tap, and eliminate the chokes, feeding the DC to the center tap.
Z for L8, L9 should be >> then the output impedance which looks like the antenna impedance for the 1:1 transformer.
I am adding a 70 watt amplifier to my uBitx, so I just need 5 watts out on all bands to drive it. I doubt I will do much more, on the transmitter, but I will have to see how the amp behaves. I may to to better equalize the output level between the bands.

Howard

On 4/19/2018 2:37 PM, Jerry Gaffke via Groups.Io wrote:

The parallel resonance helps us to a point, though an ideal inductor would generally be better.
For example, if the inductor is self resonant at 14mhz, we'd see much more power out on 20m
than we see on 10m.? I'd prefer to keep gain vs freq somewhat controlled and predicatable.

The caps are easier to add, easier to obtain, have a higher self resonance:
? ??
Maybe add 220pF caps across all six of the 22 ohm emitter resistors, and forget the inductor?
Then add a variable cap somewhere around Q90 that can be tweaked to give the flattest response,
that setting may vary given your particular 2n3904 transistor characteristics.?
?
But the inductor in series with the negative feedback is a good idea.
If this can all be done with just 3 extra components and get good enough results across
the different uBitx's out there, I'm fine with that.

One other issue:
As Henning notes in post 45035,?the chokes L8 and L9 are best wound on a single core:
See the discussion below figure 4 on this webpage, where he discusses how the bifiliar
approach works, though he does not discuss the individual choke solution:
? ??
I was seeing significantly worse results in how the uBitx final worked compared
to the WA2EBY final in my LTSpice simulation, could be due to these chokes.
? ??/g/BITX20/topic/9615903
I may have to play with that further, not obvious to me how or if the individual chokes
at L8, L9 would impact the results..

Jerry, KE7ER


On Thu, Apr 19, 2018 at 11:00 am, Jerry Gaffke wrote:

Good question.
It's a parallel resonance:??
? ??

Actually, I would prefer to rewind the transformer with a center tap, and eliminate the chokes, feeding the DC to the center tap.
Z for L8, L9 should be >> then the output impedance which looks like the antenna impedance for the 1:1 transformer.
I am adding a 70 watt amplifier to my uBitx, so I just need 5 watts out on all bands to drive it. I doubt I will do much more, on the transmitter, but I will have to see how the amp behaves. I may to to better equalize the output level between the bands.

Howard

On 4/19/2018 2:37 PM, Jerry Gaffke via Groups.Io wrote:

The parallel resonance helps us to a point, though an ideal inductor would generally be better.
For example, if the inductor is self resonant at 14mhz, we'd see much more power out on 20m
than we see on 10m.? I'd prefer to keep gain vs freq somewhat controlled and predicatable.

The caps are easier to add, easier to obtain, have a higher self resonance:
? ??
Maybe add 220pF caps across all six of the 22 ohm emitter resistors, and forget the inductor?
Then add a variable cap somewhere around Q90 that can be tweaked to give the flattest response,
that setting may vary given your particular 2n3904 transistor characteristics.?
?
But the inductor in series with the negative feedback is a good idea.
If this can all be done with just 3 extra components and get good enough results across
the different uBitx's out there, I'm fine with that.

One other issue:
As Henning notes in post 45035,?the chokes L8 and L9 are best wound on a single core:
See the discussion below figure 4 on this webpage, where he discusses how the bifiliar
approach works, though he does not discuss the individual choke solution:
? ??
I was seeing significantly worse results in how the uBitx final worked compared
to the WA2EBY final in my LTSpice simulation, could be due to these chokes.
? ??/g/BITX20/topic/9615903
I may have to play with that further, not obvious to me how or if the individual chokes
at L8, L9 would impact the results..

Jerry, KE7ER


On Thu, Apr 19, 2018 at 11:00 am, Jerry Gaffke wrote:

Good question.
It's a parallel resonance:??
? ??

The Bitx40 is my favorite radio to listen with once I did the RF gain mod via the two pin holes and cut the trace on the underside.

/g/BITX20/message/26490

I shouldn't have tombstoned the 10-ohm surface mount resistor. Just needed 2 wires and a potentiometer to be a variable resistor. Nice and quiet most days.

Here is my cigar-box uBitx with a wooden dowel Mic using the kit electret mix element and the Microsoft.

Tony, KB9A?

On Thu, Apr 19, 2018, 5:18 PM Gary Shriver <gshriver@...> wrote:

I know it’s there somewhere!!

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I know it’s there somewhere!!

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I have used these chips on many projects and used them to drive led displays, but for this application,? given the slower response of the I2C serial bus, I would stick with the given direct I/O driven LCD display and use the I2C serial to communicate with a second arduino, to add more functions. That way you keep speed, have true multitasking going on, and not only double the io, but you double memory. I plan to add an custom auto antenna tuner to mine, and a 100 watt amplifier , all in the same enclosure. I will be using a second arduino based processor to control both the filtering and switching of the amplifier in and out, and seek and search for best antenna match without having to interrupt the radio operations. That way, when auto tune is turned on, the amp will drop out to low power , the antenna will tune, and then return to the original settings. Like wise as the radio is turned to various bands, the pi filters in the amp can automatically switch with the band.
Nick
N8GIR