Project Minima has come to the end.

The distance to IW2KGW is 1569 km, report 44, antenna 3 el Beam.

The distance to SP6PYP is 789 km, report 57, antenna sky-loop 82m.

Modification not menschen earlier.

CW modulation take the signal from collector T17 and R43 connect 2,2uF and serial 180kohm to mic in.

This was adjusted after R33 220ohm changed to trim pot 500 ohm, to adjust modulation from mic.

100nF put in LP-Filter close to T+ pin (input regulator).

100nF put in LP-Filter close to +12V pin (input regulator).

I have no run QSO on 80m, 40m and 20m. I rely like the little fantastic Rig. It has built in CW memory for short CQ. Also QRSS Message not practiced yet. I think I have not found all feature yet.

It is close to unrealistic what is possible with this small rig. Width 18cm Depth 20cm Height 8cm Weight 1150 gram.

No I stopped soldering, no more measurement and go for practice with this QRP MINIMA.

If its unclear wat I have done you are welcome to email (Calsign@gmail.com) if you won’t more detail. Or put in a comment down hear.

SW is very close to Eldon Brown work really nice,  Eldons Code TANKS a Lot.

I add a Rx-preamp  +14dB its perfect when its weak signals.

Hope to her you on the band.

73 de SM4HNG Leif

Hard to get all parts in minima to working together.

I have used the receiver in the summer to listen on 80m band, when I was in the shack. Now when all puts together it starts sound very strange, I found out that the capacitor 330uF clos to LM386 Vcc was not connected! It solves this problem.

Strange behavior when modulation, needs more decoupling at mic amplifier T13 R34 10 ohm changed to 47 ohm, C43 50uF changed to 470 uF.

To get little more drive I change PA-Drive 2N3904 emitter resistor from 22 to 10 ohm, see Pa driver.

In transmit the modulation passes to LF amplifier, a FET 2N7000 shorts T15:B to ground, gate to 47kohm to +T.

Found that output is rather high even if no modulation. Put in a classic 10 turns trim pot 100 ohm to D3,D4 give around -40 dBc with no modulation.

Last problem on 21, 24 and 28 MHz is lot power when touch ptt., found out that shielding was needed between LP-Filter after PA and LP filter on main board(60 dB gain).

I will try to put up a vide as proof of working transceiver, its not a hi-tec. TRX but its working and I have learn a lot. Have made around 10 QSO, One Sweden to Netherland 59 report on 40m.

Stay tuned one last nots from this project.

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.