For measuring the noise figure of amplifiers in a 50 ohm system, noise source which generate Gaussian RF white noise are often used. Here I present a simple prototype of such a source based on two transistors and a zener diode. At the heart of the assembly is therefore a zener diode 1N759 which is the source of noise. Then this noise is amplified by an amplifier based on two BFR93A transistors. The first stage of the amplifier provides the bulk of the voltage gain, while the second allows an adaptation of the output to 50 ohms.

The voltage gain simulated under the amp’s LTspice is 16 V / V (fig.1) and the output matching to 50 ohm (fig.2) are very good on the whole band.

The proto was made on a prototyping plate. The voltage of the + 5V supply of the transistors is supplied by 7805 to have a stable behavior. The voltage of the + 15V diode supply ideally should also be regulated, however I have noticed that the generated noise hardly varies between the range of +/- 1V from the nominal voltage.

We see that with the source switched off at 50 MHz we measure a noise voltage of 36nV / sqrt (Hz), i.e. -135.9 dBm / Hz, while after switching on the noise increases to 92nV / sqrt (Hz), or -127.7 dBm / Hz. The measurement shows that the noise generated is fairly constant over the entire band. The ENR obtained from the source with respect to the thermal floor of -174 dBm / Hz is then around 46 dB.

We also notice the presence of a peak around 56 MHz which I did not understand the nature, it is probably not an oscillation because there is no harmonic of this frequency. Apart from this peak, the spectrum is clean up to 3 GHz. The next step would be to put it in a shielded box and maybe replace the proto plate with a correct PCB.

Some modifications of the broadband noise source presented previously. This second version is based on a two-stage amplifier, with the same BFR93A transistors. The difference here is that the amplifier is supplied with + 12V in order to use a 7812 regulator both for the amplifier but also for the zener diode. The stable and fixed voltage of these two parts is large enough to have a constant noise level. The zener diode used is Panasonic DZ2409100L of 9.1 V in a SMD box.

It can be seen that the voltage amplification of this version is greater, of the order of 25 dB in a 50 ohm load.

The realization is made in the same way, on a plate with hole with a good ground plane (important for the RF) which is in contact with the regulator 7812.

Finally everything is put in an aluminum box. The anodization of the case has been removed from the connections to improve the shielding.

We see that the PSD of the spectrum analyzer (HP8594E) without the noise source is -135 dBm / Hz. With the source on, however, the noise floor rises and displays a PSD that goes from -105 dBm / Hz at 1 MHz to -130 dBm / Hz at 200 MHz, which represents an ENR of up to 69 dB compared to the floor thermal of -174 dBm / Hz.

tags: balun, long wire antenna

Here I show my realization of a 1: 9 “BalUn” (actually a UnUn) for the 3-50 MHz band based on two FT114-61 toroids. The use of two toroids instead of one makes it possible to increase the power handling as well as to reduce the number of revolutions required due to the increase in the AL factor. AL measurement, made with a 5-turn winding, determined that the AL of the two tori is about 170 and the resulting inductance is 4 uH.

By putting its values ​​in LTSpice and by putting a load of 450 ohm (transformation 1: 9) at the end of the balun, we see that the latter allows a bandwidth between 3 MHz and 60 MHz for a SWR of 2: 1 (S11 < -10 dB) in the simulation.

The realization of this balun is made according to the wiring illustrated in the figure below. The winding is made with a copper wire of 1 mm in diameter. To ensure a certain seal, the balun is placed in a PVC tube.

To validate the operation of the balun in terms of impedance transformation, a measurement of S11 is made when the balun is loaded by a resistor of 470 ohm. The measurement confirms the result of the simulation and shows that the bandwidth of the balun is between 3 and 50 MHz.

Regarding power handling,
this balun has been tested several times with a transmission power of up to 50 W without any observed problems.

In the 145 MHz band, this level corresponds to -30 dBuV or 0.03 uV
In the 435 MHz band, this level corresponds to -16.5 dBuV or 0.15 uV
In the VHF band the squelch level and the corresponding voltage (10 kHz FM channel) are shown in the figure below.

Here i present my realisation of a PC link interface for Yaesu FT-100. This interface alows you to transmit and receive audio signals from a sound card in order to operate HAM digital modes (FT8, PSK31 etc.).
The PTT command is based on the work of WA2NKF (http://k0lee.com/ft100/pskft100.htm) but with an additionnal protection from OZ6YM (http://www.planker.dk) on audio channels. This protection is based on a 600 ohm 1:1 transformer and avoids the damage of the rig from a DC voltage present on the output of the soundcard.
The full diagram is shown on the fig.1 and the corresponding circuit on the fig.2 :

The NPN transistor can be a 2n2222 or a similar one, il my case i used a BCW72. The sound level on a soundcard lines is adjusted with a 1 kOhm trimmer. In order to trig the PTT a DTR (pin 4) or a RTS (pin 7) signal can be used. In my case i use a DTR
The circut was designed on KiCAD and milled on a CNC machine.

Some photos of the assembled device:

Configuration of WSJT-X and FLDigi: