[minima] Minima - Essential Modifications Errata & Notes
- From: "Steve VK2SJA" <vk2sja@xxxxxxxxxxx>
- To: minima@xxxxxxxxxxxxx
- Date: Wed, 15 Oct 2014 17:10:47 +1100
Hi Guy's,
I've been compiling a list of Errata today. This is my attempt at
gathering up all the field changes that have been discovered and reported
to this list over time.
It is my intention to create an Errata page on the HF Signals WiKi
containing this information. But I wanted to throw this out for comment
first.
Is there anything below that I've missed? Or something that I have not got
right? As many of these stages I have not yet built myself.
Note I'm trying to limit this to just the critical core circuit changes to
the original Minima circuit. Stuff that we know needs doing. Deliberately
omitting any experimental improvement stuff. Until such time as it becomes
locked-in to the design later.
Grateful for any feedback.
73, Steve.
Minima - Essential Modifications Errata & Notes
1. Q23 in the transmit/receive switching circuit. The 4.7K base resistor
should be 47K. Fixes intermittent TX/RX switching.
2. Q23 in the Low Pass Filter section (there are two Q23's in the circuit
see Notes below). The 4.7K base resistor should be 47K. Fixes intermittent
switching.
3. Q10 in the BFO circuit. The 100 ohm emitter resistor should be 1,000
ohms (1K ohms). Q10 will run excessively hot without this change.
4. Q20 in the Morse Code Tone Audio Oscillator circuit. There should be a
0.1uF capacitor between the emitter of this transistor and the two 1K
resistors. This is to provide DC blocking of 0.2V that would otherwise
reach the mixer diodes in the BFO. Fixes distortion when sending CW.
Notes:
A. The Minima RF output from the LPF's is approximately 0.025 or -16dBm.
The 1 watt RF output mentioned on the Minima introduction page is the
output level when using a Minima JBOT (Just a Bunch Of Transistors) RF
Amplifier. This amplifier was similar to a 5 watt RF amp originally
designed for use with the BitX transceivers. It had an additional stage of
amplification added to compensate for the Minima low RF drive level from
the Minima but still only produces 1 watt in combination. This amp can be
seen at http://www.hfsignals.org/index.php/File:Qrp-linear.png but has now
been superseded by the Minima RF386 Amp which drives the output to
nominally 5 watts. This amp can be seen at
http://www.hfsignals.org/index.php/RF386.
B. The audio output of the Minima is only suitable for driving headphones.
Should you wish to listen to a speaker then you will need some amplified
computer speakers (or add-to/change the audio amplifier stages in the
Minima).
C. The current Minima circuit diagram shows two Q23 transistors. One in
the LPF circuit and the other in the TX/RX switching circuit. There is no
Q12 in the circuit diagram.
D. Bias adjustment of the J-FET KISS mixer. Changes in the unwanted mixer
products are only significant at the centre tap of the T1 mixer
transformer secondary.
E. An alternate version of the USB/LSB sideband switching circuit that
uses diode switching rather than a relay is available here:
http://www.hfsignals.org/index.php/Sideband_Switching_of_BFO
Other related posts:
