"HappyHolidays TRX"
A four band VXO tuned
1 watt QRP CW transceiver

A simple, solid rig for outdoor use during Holidays.
More is possible with this solid QRP rig than you should expect.
Just try it and do not give up soon!

QRP during Holidays
A couple of years ago I made a 2 band 1 watt VXO tuned transceiver (40-20m) and took it with me on holidays to the northern countries of Europe.
When camping in the middle of nowhere, I did have daily QSO's with two amateurs in the Netherlands.
The antenna was an inverted V dipole, the centre approx. 4 meters above ground. I expected that it was almost impossible to make QSO's with such low power and such a simple rig. But it was quite easy to make a lot of QSO's and that was a great experience.

The "HappyHolidays" is a 4 band 1 watt VXO controlled transceiver, with similar performance but with more recent components and better suppression of AM detection and also intended for Holiday use.


Circuit diagram
big diagram

RF preselector and attenuator
The RF attenuator is a potentiometer of 1k ohm. An RF attenuator is always very useful to prevent overload of the first stages of a receiver. Most receivers perform better on 40 and 30 meters with some RF attenuation. Here it is also the only volume control.
The capacitors of 10, 33, 84, and 190 pF are approximate values and are combinations of trimmers and capacitors in parallel. Adjust the trimmers for maximum sensitivity.

Mixer
The mixer is one C-mos switch of the 74HC4066 (Do not use a HCT!!!). It works perfect!!!
Adjust the 5k potmeter for minimum AM detection of strong broadcast stations. If you do not have an AM signal available for adjustment, set it to centre position.

LF amplifier
Just a simple 3 transistor amplifier. The first transistor is muted during TX via the 10k resistor. The LF amplifier is optimized for CW reception with a low LF beat tone. The selectivity of the ear is very good for low audio tones up to 600 - 800 Hz, a CW filter is not really necessary.
Select the value of R1 (1200 ohm) so that in receive mode, the supply voltage of the 74HC4066 (pin 14) is approximately 5 V.


The LF amplifier is optimized for CW
but it is not a very narrow CW filter.

VXO
The VXO is a BF494 transistor, buffered via a C-mos switch. To give you an impression about the tuning ranges related to the crystal frequencies, here the values of my version without and with the optional inductors in series with the crystals for an increased tuning range.

Tuning ranges without the optional series inductors
Crystal
Frequency
(kHz)		 Minimum
Frequency
(kHz)		 Maximum
Frequency
(kHz)
7025 7024.3 7026.2
10125 10123.7 10126.5
14050 14048.2 14051.9
18080 18076.6 18080.4

Tuning ranges with the optional series inductors
Crystal
Frequency
(kHz)		 Minimum
Frequency
(kHz)		 Maximum
Frequency
(kHz)
7025 7021.1 7023.8
10125 10118.4 10123.0
14050 14039.9 14045.9
18080 18070.6 18076.4

Transmitter part
The VXO signal is buffered by a C-mos switch and amplified to 1 watt by a transistor 2N3553 or as I did, 2 transistors 2N4427 in parallel. The 1k ohm resistor makes the amplifier more stable when mismatches occur. The 0.68 uH / 180 pF and 0.47 uH / 68 pF are tuned to the second harmonic of 7 resp. 14 MHz for extra suppression.

Options

  • Battery indicator (no sidetone if battery low)
  • Key connected to ground with the possibility to use electronic keys
  • Enhanced tuning range of the VXO with inductors in series with the crystals.

    How to work with the Happy Holidays
    During transmission the VXO frequency has to be identical to that of the other station. When receiving, it needs to have an offset of 300-800 Hz, depending on the beat tone frequency you want to listen to. Therefore, it is necessary to tune the VXO approximately to zero beat with the other station just before the end of its transmission. When receiving, tune the VXO to the desired offset. In receive mode, tune the VXO offset frequency to the other side of the received signal if there is less interference on that side. After a few QSO's you will be completely used to how you have to operate the rig.

    Notes
    Built via the ugly method (dead bug method). Parts are soldered at both sides of he double sided unetched print.
    Inductances are commercially available types looking like big resistors.
    Do not use a HCT type but a HC type!

    Performance
    Sensitivity: 0.6 uV signals are readable
    3rd intercept: more than 20 dBm
    Spurious responses of the receiver: Better than -90 dB
    RX current: 10 mA
    Transmit power: 0.5 W at 9 V; 1 W at 12 V; 1.5 W at 13.5 V
    Harmonic suppression: below 30 MHz: 43 dBc, above 30 MHz: 60 dBc


    Position of switches and other controls

    Position of switches and other controls
    Place the switches so that you will have a very short wiring!
    S1 is the TX/RX switch, five other switches (S2 to S6) are used for bandswitching instead of one big complex switch.
    Place S1+S4 near the lo-pass filter, S2+S5 near the preselector filter and S3+S6 near the VXO.
    S1 should be near the lo-pass filter and also near the final RF amplifier.
    The Variable Capacitor is placed very close to the VXO.
    The RF potentiometer close to the TX/RX switch S1.
    The antenna connector of course close to the lo-pass filter output.
    The positions of the headphones connector and key input are not critical.


    Simple key (pushbutton in an old filmbox), foldable headphones, batteries and antenna.

    50 Hz or 100 Hz hum of a direct conversion receiver
    The rig is designed for use with a battery supply.
    When you use a power supply connected to the mains, it is possible that you will hear some 50 Hz / 100 Hz hum due to Local Oscillator leakage from the mixer to the antenna. This depends on the antenna, frequency band and power supply you are using. A lot of Direct Conversion receivers have this problem.
    To overcome this problem you can add the RF preamplifier as is given here below at the 21 MHz version. Increase the 270 ohm emitter resistor if the sensitivity is too high.
    Not all preamplifiers do suppress the Local Oscillator leakage from the mixer to the antenna. The first version of the preamplifier without the second transistor in the collector did not suppress the LO leakage and also an emitter follower was not usable.

    PHOTOGRAPHS


    Inside the box. The VXO is screened from the
    rest of the circuit by a verical piece of PCB.


    Both sides of the unetched PCB are fitted with components

    21 MHz version with RF preamplifier

    Why an RF preamplifier
    The RF amplifier improves the sensitivity: 0.3 uV signals are readable.
    But that is not the only reason to add the amplifier. A second, even more important reason is that it attenuates the Local Oscillator leakage from the mixer to the antenna input by 20 dB. This oscillator leakage may cause problems if you use a power supply instead of batteries, mostly on the higher bands.
    A loud 50 or 100 Hz audio tone is the result of too much Local Oscillator leakage. Without the amplifier, the 21 MHz version had this problem. With the amplifier there was no hum anymore and the sensitivity was very good.


    Schematic diagram of the 21 MHz version with RF preamplifier
    big diagram

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