Version 2016-03-06 Named ''Nose source''.
The PCB circuit received is clean and of good quality.
I will not go back over the various opinions, tests, modifications already made in the past. I'll just experiment with a new approach to modify it.
Because there is a heat problem which seems to be a recurring one with this noise source.
After a short amount of time, I can see this heat problem., The three amplifier semiconductor packages and resistors become very hot and will have a limited life span due to excessive heat.
** And more
• Don't like 24V Zener diode powered by the MC34063A (despite R11 to limit the voltage)
• Don't like MMIC's powered by 12Vdc unregulated (despite R8 / 9/10 to limit the voltage which can vary at the input).
• Output noise of the Zener source is very high
• Output after three stages of MMIC too high.
• Power density of noise is not flat towards high frequencies.
• MC34063A output is not as well filtered
• 12V DC input is not regulated.
• Then, some modifications will be made for tests.
- Powered in 12 VDC with New system on 5 Vdc power supply (regulator 5V) for MMIC'S (5v) and new zener diode.
- Input DC connector removed
- I don't use the converter 12 / 38v MC34063A (output is not as well filtered).
- L2 removed
- Zener diode replacement by a 5V and also tests with a BFR34A / BFR93 transistor
- New DC power supply with 7805 TO-220 for 3 X MMIC SBB5089Z = +5 V and zener diode.
- Addition of 10dB attenuator on output. (replacing of the 3 DB)
- R11 must be adjusted value 1 to 3k (depending diode/RF transistor).
- Installed in metal case.
- Waiting for SMD Ferrite Bead inductor to replace L3/L4/L5
The diagram below is worth less words… !!!
1st remark: At 1.5 Ghz, the curve is flatter, but the signal at higher frequencies decreases slightly. Still very usable for the quality and low price for an amateur.
(Later, some pics and probably other experiments ....)
** Update 11/09/2021
Even being in a metal case, there are self-oscillations, especially around 2.4 GHz !! it's embarassing for the WI-FI or 13cm band.
To dampen the oscillations or try to eliminate them, I added above the PCB, under the metal cover and on the 4 sides, an RF EMI ABSORBING SHEET.
The noise spectrum is even flatter and elimination of oscillations towards 2.4 Ghz.
I also replaced the L3 / L4 / L5 chokes with SMD Ferrite Bead inductors.
There is still too much signal even after changing the attenuator from 3 to 10 dB.
Before trying to remove the last MMIC, I added a 10dB on the SMA output.
(Original Schematic is from Alyx, Dodgy Engineering Rockville, MD)
