EA3GCY EGV-40, Инструкция по сборке

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EGV-40 CW QRP Transceiver Page 29
APPENDICES
Appendix 1. “PHONE” headphone output. R16 limiting resistor.
The EGV-40 has not been designed to be used with loudspeakers directly.
On the "PHONE" header you may connect only headphones. Please use adequate headphones; bad
ones will degrade the final outcome of your receiver. When checking several headphones, results will be
very different and for us, hams, in many cases the most expensive headphones are not the best.
Sometimes low cost headphones may result ideal for the purpose of listening to the EGV-40; this may be
due to their sensitivity and the audio response, which may fit better the bandwidth required for the CW
signals.
If you plan to use the EGV-40 at home, you may get very good results with PC multimedia speakers with
their own amplifier (use 2.0 types of good quality, as systems with “sub-woofer” or "home cinema" are
not adequate.)
-R16 limits the output level to the headphones and protects the audio amplifier in case of a shortcircuit at
the output.
Appendix 2. Transmitter power amplifier transistor Q12.
The 2SC2078 transistor included with the kit has been selected for the EGV for being a good output
transistor for HF.
In case of need you may use others. Some transistors used on CB transceiver such as the 2SC2166 or
2SC1969 may be also used and offer a similar result. In some cases the terminal distribution is different.
The bridges “B, E, C” - “x, y, z” will allow you to use any kind of TO-220 transistor as Q12.
Notes:
- Some transistors may have higher gain and, depending on their manufacturer, may be prone to auto-
oscillations.
- Many of this kind of HF transistors offered in the market at low price are fakes and work bad or do not
work at all.
Appendix 3. The VXO as local oscillator.
Why are we using a VXO?
The classical -and economical- alternative to the VXO is a simple Variable Frequency Oscillator (VFO) or
a Voltage Controlled Oscillator (VCO). In order to get very clean mixing products when an heterodyne
system is used, it is recommended for both RX and, especially, for TX to use a Local Oscillator (LO)
located over the Intermediate Frequency (IF), in our case 4.915 MHz, and over the working frequency, in
our case 7.000 MHz. It will be possible to build a VFO LO on 2.085 - 2.125 MHz quite cheap and stable,
but the mixing products on RX and TX will not be as clean as the ones produced with an LO on 11.9
MHz, as generated on the EGV-40 VXO.
The other option, a PLL driven VCO, will be adequate but expensive and cumbersome taking into
account the number of parts required.
If you want to have a very precise transceiver, with high stability and digital dial, an excellent alternative
is the use of a DDS circuit. I will recommend you the ILER-DDS from EA3GCY.
Note:
If you have bought the EGV-40 and the ILER-DDS you don't need to install any of the parts related to the
VXO circuit. Please see Appendix 7.
Appendix 4. Sidetone level. R6 value.
The sidetone level is fixed by R6. With the R6 resistor included with the kit the sidetone level is sufficient
but soft. You may change the value between 1 M and 10 M to get the required level.