SM5CJW Fox-Receiver 2014

Now the fox receiver is working, murphy is in the first one it has bad sensitivity. I will fix this later. The PCB was shown in this blog 8 October. This second one I can here -130 dBm signal from my generator.  So I have start the mechanical work to put it in a metal box. There is needed a sense antenna.  Lock forward to the spring and nice fox-orienting.

Minima Crystal filter

Started to measure all 30 pcs i have. 2 was really bad i put them in the wastebasket (nr 15, 19 ). Putt all f values in a spread sheet. Then it is simple to select the 8 X-tal with the closest frequencies. I put them on a pcb. and use 100pF as original loading capacitor, this give around 4kHz bw, try 200 pF but tis give below 2 kHz bw. Then I order 180 pF.

After testing this I try to change order of the X-tal, the effect was minimal, time to put them on the minima board. This measurement is on the minima board. Note the 3dB point and try to adjust BFO to +/- 400 Hz was not possible so i must change the circuit to succeed.

In teori the X-tal should not be mor spred then +/- 5% off BW 2.4 kHz means +/- 120 Hz the best 8 pcs i have spred -160 + 145 Hz, here is the result measured when mounting on the pcb.

After all I put murphy out of the shack and will son start the last step with the LP- filter,

stay tuned SM4HNG Leif.

Minima Mixer

The mixer is now on the board. I start winding the two BN43–2402 5,5 turn. Then select 2 off the 10 pcs J310 fet, with the closest Ids current. Mounted all mixer components on  the pcb. First try to adjust the bias to the fet. I have seen youtube video saying there is no difference in output, but I could see 3 dB change in amplitude on IF signal at 20MHz and also around 5dB in change of Noise-Flore best on 3,5 MHz was 2,5V and best on 28 MHz was 3,5V so I set bias in middle 3,0 V.

The spectrum is, what coms in coms out.

This measurement give me the conversion loss. Input 3,75, 17,2 and 28,4 Mhz around -52 dBm, this result in around 7 dB conversen loss, i also check @ 144 MHz input around 12dB loss.

The Isolation on IF port and RF port.  Lo is +16 dBm

Isolation @ IF port23,75 around 44 dB 37,2 around 41 dB 48,4 MHz around 38 dB.

it is worse on RF port.

Isolation @ RF port 37,2 MHz around 17 dB, its better at lower and higher freqv. 27 dB. 

After that I check impedance on the port.

Lo Port

 IF Port

RF port 

Perhaps it possible to get better figures more close to 50 ohm, but life is not always perfect!

I am glad that its time for X-Tal filer Test……….

73 de Leif SM4HNG