Low noise pre-amplifier for ADS-B reception

Two weeks ago, my son asked me to donate him the RTL SDR and the old antenna for ADS-B, to join FR24 network. I said yes, and I re-install the antenna, unfortunely not so high as needed, not with proper coaxial, etc. After 30 minutes the set-up was ready. After few days, I checked the results and I found the maximum range 115 nm and only 600 aircrafts seen daily. I said is normal for an antenna obstructed and 10 meters RG58 cable (let say, 6 dB losses, at 1090 Mhz).

On the other hand, I stopped any hamradio QSO, because I was afraid to not destroy the SDR, without a proper filter (the distance between my delta loop and 1090 antenna is about 4 meters).

So, I passed to next step, building a cavity resonator and finding a good pre-amplifier. For the moment I am not very hapy with the filter I have build, but I shall let you know later… after I shall can tell you what not to do when you build a filter !!!

I found in my junk box an old antenna (with the housing broken) with an GPS antenna and a pre-amplifier inside.

The amplifier is build with 2 transistor, the 1st is a sms marked V80. I found the datasheets, is a NE3509M04, Ga-As transistor, NF=0.4dB, Ga=17.5dB. The total gain of the module it seems to be up to 25 dB.

Now, the order of operation.

Remove the shield and the ceramic antenna

Remove the filter and coaxial cable used for output (it was cutted and too short)

Solder a capacitor to replace the filter and connect 1st stage to the 2nd stage of amplifier. If you dont have a very small capacitor (as dimension), somewhere between 1-5,6 pF, you can use twisted wires.

For connecting the signal to input, you shall find very easy the pads on the other side of the pcb. In the middle is the center of the coaxial, the rest is ground.

Solder the coaxial to input, output, solder back the shield, build a 3 – 5 Vcc stabilizer, connect the antenna through a filter (this will be another story), and conect to the SDR.

The practical improvements of reception: increasing the reception range from 115 nm to 145 nm, increasing the no of aircraft seen from aprox 600 daily to 750 daily, from maximum 50 reports daily from more than 100 nm, to minimum 1200 reports daily from more than 100 nm.

As I said, about cavity filter, next time. I didnt have enough time to make all the possibil mistakes !!! (what is running now, it looks like a cavity, but only looks).



Eggbeater antenna – 145 Mhz

My first adventure with the eggbeater antenna took place 1 year ago when I made this antenna for 137Mhz weather satellites.
Few months ago I tried to listen the satellites trasmitting on 2 m band. So, I modified the old antenna for new frequency, this time using a Rig Expert AA230 for final testing.
I was inspired from documentation writen by ON6WG/F5VIF (you can download from his website, https://on6wg.pagesperso-orange.fr/Page%201.html).
For building the loops I used flat aluminium (15 x 2 mm), you can find in bricolaje store at 2.6 meters lenght. The circumference of the loops is 212 cm. For mounting, I used 50 mm pvc water pipes and textolit.

The ground reflector was made with 8mm aluminium rods, 4 pcs x 53 cm lenght, conected in center and mounted at 27 cm under loops.

The most important job was the feeding harness. I used the ON6WG recommendation (https://on6wg.pagesperso-orange.fr/Doc/Appendix%20A%20-%20English.pdf)
You can find on page 3 all the formulas you need to calculate all the dimensions. I used RG58, because is very hard to insert H1000 or other low loss cables into 50 mm pvc pipe.
So, nothing new. What can I add to ON6WG work are the AA230 tests.
It is an antenna easy to build, does not require adjustments, if you read carefully the documentation. The results "can" be listen... 
XW-2C satellite

73's, Cristian - YO4DFT

FT920 + SCU 17 – AFSK settings – digital modes

FT920 - data conector pinout
SCU-17 conector pinout (As viewed from rear panel, not from cable!) 

AFSK mode
FT-920 pin 1 Data IN (Audio IN)	     SCU-17 pin 1 Data OUT (Audio OUT)
FT-920 pin 2 GND	             SCU-17 pin 2 GND
FT-920 pin 3 PTT	             SCU-17 pin 3 PTT
FT-920 pin 4 Data OUT (Audio OUT)    SCU-17 pin 5 Data IN (Audio IN)
FT-920 pin 5 Busy	             SCU-17 pin 6 SQL IN (Busy)
Pin 1 (AFSK Input):
Connect this pin to your TNC’s “AFSK Out” or “Mic Audio” output line. The optimum input level is 30mV rms, and the input impedance is 3 k. Your TNC’s audio output level potentiometer will allow you to set the level to the optimum value. This pinmay be used either for 300 baud SSB-mode digital operation or for 1200-baud FM packet. The bandwidth and frequency response are not, however, suitable for 9600 baud operation. Be sure the AFSK-FSK switch on the rear panel is in the AFSK position. For FSK operation (whereby the TNC closes a line to ground to accomplish teletype keying), set the AFSK-FSK switch to FSK, and connect your
TNC’s FSK keying line to Pin 1.

Pin 2 (Ground):
Connect this to the shield(s) of the cable(s) used for connections between the TNC and the FT-920.

Pin 3 (PTT):
Connect this pin to the PTT line from the TNC. This pin, when grounded by the TNC, places the FT-920 into the Transmit condition.

Pin 4 (Audio Out):
Connect this pin to your TNC’s “RX Audio” input line. This is a constant-level (100 mV rms @ 600) audio output line which is not affected by the position of the front-panel AF GAIN control.

Pin 5 (BUSY):
This is a “Squelch Status” pin not generally required for digital mode operation. This pin is held at +5V when the squelch is open, and is grounded when the receiver is muted by the squelch (“nosignal” condition).

FT920 Menu settings (dont forget - USB-DATA mode)

Menu #    Description                   Value for WSPR/FT4/FT8/RTTY
U-45      Packet Freq. Display Offset   0000
U-46      Packet Subcarrier Frequency   2125U

Please note, those values are available for regular rtty tones (2295/2125).