EGV-40 CW QRP Transceiver
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Appendix 5. Full-Break-in delay. C17 value.
The TX/RX switching delay may be modified by exchanging C17 with a cap of different value. The kit
includes a C17 cap of 100nF, getting a delay of 300-400 ms. You may increase or reduce the value of
C17 to increase or reduce the delay. If you remove C17, you will be able to work with Full Break-in, but it
is recommended to include a small capacitor to get a delay of some tens of ms to avoid switching clicks
and noises.
Appendix 6. “Fine tune” coverage
The P3 control acts as a fine tuning associated to the main tuning carried out by the polyvaricon and,
obviously,
they both work on RX and TX.
If you prefer to use a mechanical reduction on the shaft of the polyvaricon or a larger diameter button,
you may disable the P3 pot but just removing it from the PCB; we recommend that, instead, you place
two 4K7 resistors to keep the overall coverage of the VXO as previously adjusted. If you remove
completely the "Fine tuning" circuit, including the DV1 varicap diode, the upper frequency limit may lie
above the CW segment with no adjustment possible to lower it.
The "Fine tuning" control changes 1-2 kHz in the lower part of the coverage range and 5-6 kHz in the
upper part. This is due to the nature of the circuit, the lack of linearity on the tuning circuit, and the fact
that a similar change on the capacity external to the polyvaricon affects differently to the tuned frequency
depending on the part of the band.
Use of the “Fine tuning” control
We recommend to place it normally on its mid position. Once you have find a station with the Main tuning
control, move the Fine tuning to tune it spot on. Once you have finished the QSO, or when you want to
search for other stations, return first the Fine tuning control to its mid position.
Note: You may change the coverage of the “Fine tuning” control by changing the value of the capacitor
C31 and/or the resistor R18.
Appendix 7. Use of the ILER-DDS with the EGV-40
The ILER-DDS offers a high stability oscillator against temperature changes, with a 10 Hz resolution and
frequency reading on an LCD. Moreover, the ILER-DDS may be configured to work with any other IF
value, place band limits, quickly change the tuning steps, display the PSU voltage, etc.
-If you have a working EGV-40 with its VXO and want to install an ILER-DDS, you need to disable the
VXO by just disconnecting L6 and connecting the DDS output to the "VXO" header on the EGV-40.
-If you have bought the EGV-40 and the ILER-DDS and you want to install it from scratch you don't need
to install any of the parts related to the VXO circuit with the exception of R26.
The following list gathers the parts related to the VXO that you don't need to install if you plan to use
always the rig with the ILER-DDS:
R18, P3, R19, R20, R21, R22, R23, R24, R25, and pot P3
C30, C31, C32, C33, C34, C35, C36, C37, C38, and Polyvaricon CV2/CV3
L6, DV1, Q7, Q8, IC5, X5, and X6
Appendix 8. IF bandwith
The nominal bandwidth of the IF filter is of 800 Hz (at -6 dB). This offers a good selectivity for an easy
listening of the CW signals. The IF bandwidth, however, may be modified by simply exchanging the caps
on C8 and C9. You may reduce their value down to 100 pf to get a wider bandwidth (less selectivity).
This change produces some mismatches on the terminating impedance and the ripple on the filter
response may increase, but most of the time you will not notice it.