Low pass filter for Minima

I need a Lp filter to put after the PA-2008. I made a copy of the original design and add 2 pcs. off 5v regulator. My relay is 5V. I made simulation of the filter in ELSIE program. The result from Elsie is to optimistically. Perhaps I should have use heavier wire in the inductor. If more stop attenuation is wonted, I think better layout and more shielding is needed.

Here is the ELSIE simulation.

Her is the real result only filter on PCB.

Here is the measurment, in - out of the PCB.

I hope it has been better but here is the result.

I have run a first QSO, but Murphy is with me, i will come bake, stay tuned.

Minima QRP Transceiver Setup

I won’t to describe a little off the process to get this Minima up and running. Early in the spring I set up this pc board to put main board and digital board connected, and to check tx and rx.

BFO.

First problem I could not hear any station clear SSB, I figured out that the bfo. was on the wrong side,  lo is over  f0, see BFO wrong. This is now changed so it is working.

Filter.

Next problem was filter 15-30 MHz didn’t switch in when move to 18MHz. I think it was hw problem check agene now fault. Time to lock at sw. and there it was, I added this line,

pinMode(BAND_HI, OUTPUT); ?

and now it works , original from Radiono - The Minima's Main Arduino Sketch.

Modulation.

The rx. woks fine listening on 80m. But tricky to get power out. I try to put out mic signal and ston, to modulate. The level at modulator is low. I have build Bitex or more exactly MKARS80 and it works grate from beginning, the difference is a emitter-follower. I build this on my board, it dossent effect rx level much.

Now I can have a grate signal on modulator.

Next the ston. is a bit low for monitoring, change R41 10 ohm to 22 ohm value sounds ok. But for modulation docent work. Try signal from T13 collector its much higher, but impedance in mic stage is to low so one possibility is to connect at mic input, I will fine tune later. I also change emitter resistor 220 ohm to a trim pot, 500 ohm, to adjust mic level

Button.

The SW. WA0UWH has made locks grate so I decided to install 7 buttons for the final setup.

I am now working hard to get the LP-Filter after the PA to work,

Theoretical loss and loss in practical. Stay tuned I will be back.

Minima PA Driver and Rx Preamplifier

Minima PA Driver and Rx Preamplifier.

I start at locking in the book Experimental Methods in RF Design, page 2.32. There was a good example on a amplifier for higher Pout then I need, so I lower the current. I do a test and find it working. I add a Rx preamp switchable in/out amplifier, copy from a QRP station.

Made a PCB and it is now finished.

The Result, gain 1.8 MHz 32 dB, 30 MHz 29 dB.

Pa for the Minima Transceiver  QRP Pa 2008

I make a decision to by this kit instead for doing the RF386 pa for Minima. After build, I put the transistor on a sheet  of aluminum. Adjust bias and start test.

Power in +10dBm.  Vin = 13,5 V.

Frequency       Power                Current

3,5 MHz             12W                    1,53A  

7,1 MHz             13,2W                1,57A

14,2 MHz          13,2W                1,43A

21,2 MHz          8,5W                   1,31A

28,5 MHz          7,9 W                  1,27A

I bye the kit here.

Excellent Measurements. Here by IN3OTD.

Si5351

Si5351

I lock so much at info about this module so i order one from Adafruit.

Breakout Board

After that I came over this really inspired, QRP homebuilding transceiver from qrparci, presented in Januari number, and here . So I play around with it, couldn’t get the code to compile so I change to the AdafruitRSGBLcd display I have. The performance locks ok for QRP, lots of info here   NT7S .

8 kHz – 160 MHz , I measure around -2 dBm out @ 50ohm on f0.

I really like VFO + BFO on this small board. I will try it in one of my project later on.

TFT Display 2.4”

#include "SPI.h"

#include "Adafruit_GFX.h"

#include "Adafruit_ILI9340.h"

ADS7846 Touch-Controller

One day in summer i tested the TFT display 2,4” 240*320. I tested different library. The best I tested was this Adafruit_ILI9340 and the library Adafruit_GFX.h. Just convert signal I/O from 5V to 3,3V change the pin number and all works. Tested some writing. The Code did as in this video TFT video if I remember correct. Also weird up SD card and wives the parrot and sunset.bmp. Tested a simple code for touch screen, ADS7846 Touch-Controller. This will be the display for next QRP station.

Fox Transmitter 80M now Working

 

This work started in Januari 80m Fox it has now came to the end.

The Fox-Transmitter fail in the beginning of the same week that i wont to use them for a competition her in Sweden. Two of the foxes burn up the FET IRF510 after a few minutes. I have a older board off this type and it has run for several years.  As I understand the problem is the high capacitance between terminals on this FET. It was not possible to load the gate more (1k ohm). So I tried to change the FET to a NPN transistor BC139 and it looks promising. I change 2 components R to C and put in R on not used pads. 5 Foxes has now been working for several hours, and in a small competitions W31. But it was a hard fight against  Murphy. I will build 2 more this winter. Stay tuned.  My son has also updated the SW with more Features. I f you won more info please contact me.

Fox Receiver 2m

Sam weeks ago i found that the ARDF resources from G3ZOI was updated. URL fox description I like this design wary good. So I ordered one bored and this arrived a few days later, PCB + 2 potentiometers, 3.5 mm jack for earphone and 2 Led, soldered and aligned. Order a box from Elfa 10-431-36 Aluminium 115 x 64 x 30 mm 1550B. I won’t little different setup see picture, possible to operate attenuator and pejel with one hand. Already use a old antenna. Fox Antenna Is made after this info. Use Isolated SMA connector and can easy change antenna.

Testing on Lab bench.

 

Current 13.6 mA.

Frequency 143,6 – 145,0 MHz

 

Input            RSSI pin 7.

-100 dBm    0,98V

-90                1,16

-80                1,40

-70                1.66

-60                1,84

-50                2,0

-40                2,23

-30                2,45

-26                2,5 max.

 

MinDetectebelSignal  around -120dBm

 

To turn on led1 red it needs maximum signal -30 dBm.

I measure Led1 Vforward around 1.8V if I remember correct.

I use one Elfa 75-036-76 it turns on 1,6V with the same current. Now Led1 turns on earlier.

 

Practice at home 3 Km away strong signals excellent reception.

Red diode lightning 100 - 150m before Fox.

2015-04-24 First Competition. Bad result, but excellent receiver especial I like the pitch it helps to determine the exact direction, When Red diode on, take exact bearing and catch the fox.

 

It is my third 2m Fox receiver and the best I have.

Minima Input-filter

This is the 15 MHz filter RF OUT - C13

This is the 30 MHz filter RF OUT - C8

This is the notch L7, CT3, L9, CT2, L11, CT1

This is the 30 MHz filter RF OUT - C8 and notch.

This is the 30 MHz filter RF OUT - C8 and notch and K1.

First comment  L1, L5 is 0,68uH and L2, L3, L4 is 0,82uH. Notch L7, L9, L11 is 3,3uH I check in filter-program Elsie before I order inductor and the effect was small.

I think the vna-plot says more than a lot of data or word. The notch is not so selective so it effect the 21MHz band, perhaps it is possible to compensate with preamplifier. Locking at the plot it can be possible to change IF to 16 MHz -1,65 to 14MHz and + 2,68 MHz to 18 MHz band. Chang lo-filter to 10 to 12 MHz cut off.

I think it is better to have tow small relays in sted of one, the K1 on this solution I work with (pp2kr pcb). I think this is the reason way there is les attenuations in the last plot. K1 serves out and in of the filters.

  Here is the result a finished board.

Next step is to load original sw and start playing with it the receiver. I will be back in May stay tuned.

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