A VERY SIMPLE RECEIVER
(2005)

KLIK HIER VOOR DE NEDERLANDSE VERSIE


The very simple receiver for the whole shortwave band.
Regenerative control, tuning, band selection, it has everything.
Even a fine tuning by moving your hand towards the coil!

Real Barefoot Technology: very simple with only one active component!
"Barefoot" technology or simple, cheap and harmless technology. It was certainly not the intention to make a good receiver. No, the question was what you can receive with a very simple receiver with only one active component (transistor, tube or fet). Well, that was more than expected. With this very simple receiver, many radio amateur stations can be heard with a wire antenna of 5 meters. The receiver is tested on 80, 40, 30 and 20 meters but the higher frequency bands can also be received. For 160 meter, the coil needs to have some more windings or an extra capacitor has to be switched in parallel with the variable capacitor.


Top view, the coil in use for 80 meter.
Fine tuning by moving your hand from or towards the coil!

To play and experiments!
The control of such a simple receiver is totally different than working with a complicated transceiver. Especially the fine tuning by moving your hand towards the coil is a special experience, just like searching for the correct taps of the coils. It gives you a good impression about how it was in the beginning of radio. Therefore, experimenting with such a simple receiver is a nice activity, also because you should not expect that it is possible to receive so much with it.

Low battery current!
The battery current is only 0,5 mA. Therefore, the battery life is one year if you use the receiver 2 hours per day!

For beginners???
For a beginner, it is certainly a nice homebrew project and a nice receiver for the strong shortwave broadcast stations. This radio is so simple that the construction of it cannot go wrong! A disadvantage is that you do need sensitive (and expensive) headphones for the reception of SSB signals of radio amateurs, otherwise these signals are very weak. Unexperienced shortwave listeners will have to practice a lot before they can tune this receiver correctly for SSB signals and probably be disappointed because they did expect much more of this simple receiver
It was allowed to use only one active component. But when you add an extra LF transistor stage, you can delete the audio transformer of Euro 7.50 and also use less sensitive and cheaper headphones!

Description
The heart of the circuit is the fet BF256c (c type has the highest gain). By means of the 5600 ohm resistor, it works in the non- linear part of the Id/Vgs characteristic. Experiment with that value in your receiver for better performance. The 10uF capacitor is for decoupling of the resistor, also for high frequencies. Perhaps that you need to add an extra 0.1uF capacitor in parallel for decoupling of the RF frequencies but I did not hear any difference. The regeneration is controlled by means of the 10k potentiometer. Adjust it for maximum sensitivity. The audio transformer is necessary for impedance matching between the fet and the headphones. The 5000 ohm primary tap was selected here at first, later the 10000 ohm. Of course you can use also another transformer. Even a 230 volt / 12 volt transformer from and old mains adapter is often useable, just try it. The headphones used is a Philips, model HS415. Sensitivity is very good, both earpieces are connected in parallel.


Schematic diagram of the simple receiver.
Sorry for the Dutch text but you will understand it after reading this article.

big diagram

Regenerative control
Regeneration takes place by connecting the source of the fet to a tap of the coil. Regeneration is controlled by means of the 10k potentiometer, less or more signal goes via the potentiometer instead of via the tap of the coil.
Regeneration occurs only if the drain has a capacitive coupling with ground. That happens here via the existing capacitances of the audio transformer (primary/secundary) and/or via the battery. If the capacitance is insufficient, connect a capacitor of 10nF between drain and ground, that gives also some extra audio selectivity (attenuation of high tones). You should expect that the adjustment of the regeneration influences the tuning frequency considerably. But in practice, that is not the case.

Coarse tuning with the variable capacitor and fine tuning with your hand
The various shortwave bands can be selected by shortening a part of the coil from the top. Coarse tuning can be done with the variable capacitor. There is a very simple solution for the fine tuning: Move your hand towards or from the coil. With this fine tuning, it is possible to tune the whole 30 meter band and also the CW or SSB part of the 40 meter band!

Automatic frequency correction
As you will understand, the stability of the receiver is not so good because there is a direct coupling of the oscillator with the antenna and the construction is very open without any screening. But the fine tuning with your hand is also an automatic frequency correction! You will move your hand automatically to correct for the frequency drift.

The coil
The coil is wound with 1,5mm solid copper wire (black) on a square strip of wood of 28x28 mm. The windings with a tap are pulled upwards a little and the isolation is removed..The antenna, source of the fet and the short from the top are connected to these taps with crocodile clips. The correct tap is determined experimentally by ear. There is also a tap on zero windings. This is located in the middle of the connection between the coil and the ground of the tuning capacitor.


The coil in use for 20 meter.


The coil in use for 40 meter.
In the evening, the antenna is connected to tap 0 (a few cm from ground).
At tap 1 the receiver is overloaded then by the strong signals.

Results
The sensitivity is approximately 4 microvolt on all bands, that will say that CW signals of 4 microvolt can be received without any problem. With some extra effort it is possible to receiver signals of 2 microvolt.
In practice, you can receive CW signals of S6 to S7 and S7 to S8 for SSB. As the majority of signals has at least this strength, there is much to hear! Especially on 80, 40 and 30 meters, the reception is excellent. But also on 20 and 17 meters many signals are heard.
It is recommended to use a low pass filter on 80 meters in the evening (for example an antenna tuner). Otherwise you will have much trouble with whistles caused by the very strong broadcast transmitters on the second harmonic. On the other bands you do not have this problem.


WHAT CAN YOU HEAR WITH SUCH A SIMPLE RECEIVER

Below an impression about what you can receive. There is not really tried to receive as many stations as possible, so now and then I listened for a while to some QSO's.

80 METER, 15 AUGUST 2005, 1830 - 1939 GMT
Listened the first half hour to the transmission of the club station of PI4AA. Excellent signal! The other stations are heard in the second half hour.
80 meter SSB:
PI4AA (excellent, some interference)
PE1NXK (weak, no interference)
PA2JWN (good, no interference)
PA2AD (good, no interference)
PA3ESU (good, no interference)
PE1ABT (weak, no interference)
DL9HAM (excellent, some interference)
80 meter CW:
G0TMX (very good, no interference)
F6EJN (very good, no interference)
G3VRU (very good, some interference)
SM5COP (very good, no interference)
G3SES (good, no interference)
G0SZR (good, no interference)
OM3KAP (good, much interference)
G3SES (good, no interference)
DJ4EL (good, some interference)

40 METER, 23 AUGUST 2005, 1852 - 1954 GMT
Also many long QSO's so that it was difficult to get the calls because they were not given very often or in a foreign languaged.
40 meter SSB:
DH3RS (good, some interference)
DL7HKL (very good, some interference)
DL4MA (good, some interference)
M0JED (very good, much interference)
ON4KPR (very good, some interference)
M3DOQ (good, some interference)
F6FJH (good, some interference)
DC4DG (good, some interference)
OK1BN (very good, much interference)
DF1WR (very good, some interference)
OE6RLF (good, some interference)
G0CBW (good, some interference)
40 meter CW:
DJ5MZ (very good, some interference)
SM1OII (very good, some interference)
IK1JJH (good, some interference)
RL3AF (good, much interference)
DL7YAV (good, much interference)
HA3OD (good, some interference)
DL8PG (very good, much interference)
UA9UFO (good, some interference)
G3HNC (very good, some interference)
PC7CW (good, some interference)
DL0AU (good, much interference)
EA7GV (good, some interference)
EA7CJN (good, some interference)
DJ6ZM (very good, some interference)
HA5BDM (good, some interference)
RW3AA/P (good, some interference)
DL4CH (good, some interference)

30 METER, 16 AUGUST 2005, 1821 - 1900 GMT en 2014 - 2054 GMT
There are no SSB stations on 30 meter. In CW, it is much easier to get the calls than in SSB as foreign languages are not a problem in CW.
30 meter SSB:
No SSB stations on 30 meter
30 meter CW:
EU3DN (good, some interference)
OE1ZL (good, some interference)
G3JUX (weak, some interference)
OE5CSP (good, much interference)
ND9M/MM (good, some interference)
OM8AG (very good, some interference)
LA2U (good, some interference)
S59AA (good, some interference)
S52VP (very good, no interference)
SN25SOL (very good, no interference)
IK2WXW (very good, no interference)
SQ9I (good, some interference)
LY2ER (very good, much interference)
DQ5M (good, some interference)
YU1FE (very good, some interference)
LY2PX (good, some interference)
T94DO (good, much interference)
GM4KGK (good, some interference)
M0NLD (weak, some interference)
IZ0FZQ (good, some interference)
F5BPM (very good, some interference)
JA4FHE (very good!, some interference)
EA2PA (weak, some interference)
F5PRH (good, some interference)
G3NQF (very good, some interference)
OK2WK (good, some interference)
IK0NOJ (good, some interference)
UA3QXD (weak, some interference)
DL3KVR (very good, some interference)
RZ3EA (good, some interference)

20 METER, 19 AUGUST 2005, 1905 - 2009 GMT
On 20 meter often short QSO's with the calls clearly spelled.
20 meter SSB:
K4KAL (good, some interference)
EA7HW (very good, some interference)
RL3FT (very good, some interference)
SV9GPV (good, some interference)
OE4XRK (excellent, no interference)
RK3XXA/P (very good, no interference)
CN8SG (very good, some interference)
S58AL (excellent, no interference)
IS6BXV (good, some interference)
US4IXQ (excellent, much interference)
ER4DX (excellent, much interference)
20 meter CW:
K4EJQ (good, some interference)
W2YJ (good, some interference)
UT7LM (very good, some interference)
W4PKU (very good, some interference)
HA1KXX (very good, no interference)
S8IDX (good, no interference)
UA3TN (good, no interference)
EA5BZJ (very good, some interference)
RW6BD (good, some interference)
YO4PP (good, no interference)
IK1ATK (good, some interference)
UA3AO (very good, some interference)
US5FA (very good, some interference)
YU1XI (very good, some interference)

My frequency scale
The next table is used as a scale to tune to the various bands.
The 5.3 MHz band is an amateurband that is used in the UK.
The sensitivity on 15 meter is less good, the reason is not found yet.

BandAntenna tapSource tapTop tapTune
(degrees)
Sensitivity
803 (2.5wdg)4 (4.5wdg)12 (35wdg)2704 uV
801 (0.5wdg)3 (2.5wdg)12 (35wdg)2708 uV
5.3 MHz3 (2.5wdg)4 (4.5wdg)12 (35wdg)3654 uV
5.3 MHz2 (1.5wdg)4 (4.5wdg)12 (35wdg)3654 uV
401 (0.5wdg)2 (1.5wdg)8 (19wdg)3504 uV
400 (wire)1 (0.5wdg)8 (19wdg)35016 uV
301 (0.5wdg)2 (1.5wdg)6 (11wdg)3554 uV
201 (0.5wdg)2 (1.5wdg)6 (11wdg)360+954 uV
171 (0.5wdg)2 (1.5wdg)5 (7wdg)360+904 uV
150 (wire)1 (0.5wdg)5 (7wdg)360+1308 uV
120 (wire)1 (0.5wdg)4 (4.5wdg)360+1204 uV
100 (wire)1 (0.5wdg)4 (4.5wdg)360+1704 uV


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