Thursday, 18 June 2009

Class A amp LTspice Model

Class A Amplifier from Experimental Methods in RF Design (EMRFD) Fig. 2.29.

I found a way in LTspice that you can simulate several signal drive levels to give various output waveforms.

Here the graphic shows at 20mV AC drive a nice sinusoidal O/P on the collector. As we increase the drive level the transistor goes into saturation and the output wave form appears clipped as the collector voltage appoaches the Voltage supply at 10V and thus the causing the collector curent to drop to zero. At the exteme input drive level the collector has dropped below the base voltage and the transistor is shown saturated for the bottom part of the curve.

It was nice to model an amplifier this way to show the effect of non-linearity behavior. The Spice models shown are similiar to the curves shown in EMRFD Fig2.30.


The spice model includes a Spice directive that basically switches in each voltage source given by the .param and .step function. The B1 symbol is an arbitary behavioural voltage source symbol and not a voltage source symbol which caught me out.

Wednesday, 17 June 2009

WSPR

WSPR - Pronounced whisper stands for Weak signal propogation network.

WSPR is basically a propogation network of low power Beacons operated by hams all over the world.

I tried it out for the first time tonight
after seeing a posting on a Web page on how easy it was to set-up. As I already had an interface box to connect up my Icom IC-735 to the PC for PSK31 I thought I would give it a try. The software to run WSPR can be found here on K1JT's Website.
After downloading it, you need to configure the Setup - option page at the top of the program. Details can be found on the WSPR program Help page. Next You need to ensure that your computer is correct to within 1 sec for the program to decode the incoming received signals. On Windows XP that is done by clicking the time at the bottom of the desktop and selecting adjust/date time. In the Date and Time properties box click the Internet time tab and then press update to synchronise the clock to one of the universal time standard servers.

The radio receive frequency has to be manually set to the default frequency shown on the WSPR program as there is no CAT control to the transceiver. To select the Transmit frequency just double click on the water fall display, I usaully set the T/R cycle to 20%. Just this evening alone I received a report from VK wow!!. My transmit power was only 1 Watt into a 102ft Doublet 30ft high.

My tribulations in connecting my Laptop upto the Transceiver is another story, and hopefully will document in a further blog entry.

G4ILO has written a very good write up and tutorial on operating WSPR.

This is my signal received by other stations.

TimestampCallMHzSNRDriftGridPwrReporterRGridkmaz
2009-06-17 23:20 G0BON 14.097089 -24 -1 IO91qm 1 VK8CH PH57 13894 63
2009-06-17 23:20 G0BON 14.097088 -22 -1 IO91qm 1 DH5RAE JN68pv 1031 101
2009-06-17 23:20 G0BON 14.097091 -26 -1 IO91qm 1 K3SIW EN52ta 6357 298
2009-06-17 22:50 G0BON 14.097088 -19 -1 IO91qm 1 VK8CH PH57 13894 63
2009-06-17 22:50 G0BON 14.097085 -24 -1 IO91qm 1 DH5RAE JN68pv 1031 101
2009-06-17 22:22 G0BON 10.140241 -24 -1 IO91qm 1 RA1AMO KO59cw 2119 52
2009-06-17 22:16 G0BON 10.140242 -28 -1 IO91qm 1 RA1AMO KO59cw 2119 52
2009-06-17 21:52 G0BON 10.140237 -27 -1 IO91qm 1 RA1AMO KO59cw 2119 52
2009-06-17 21:10 G0BON 10.140206 -26 -1 IO91 5 W3CSW FM19kd 5827 288

This is my report to other stations

TimestampCallMHzSNRDriftGridPwrReporterRGridkmaz
2009-06-17 23:00 DL8BB 14.097060 -10 0 JO41ul 5 G0BON IO91qm 715 274
2009-06-17 22:56 AI4RY 14.097119 -20 1 EM72go 5 G0BON IO91qm 6897 45
2009-06-17 22:54 K3SIW 14.097198 -10 0 EN52ta 1 G0BON IO91qm 6357 48
2009-06-17 22:54 WB4KLJ 14.097182 -25 0 FM18ku 2 G0BON IO91qm 5874 49
2009-06-17 22:43 K3SIW 14.097197 -14 0 EN52ta 1 G0BON IO91qm 6357 48
2009-06-17 22:43 WB4KLJ 14.097181 -24 0 FM18ku 2 G0BON IO91qm 5874 49
2009-06-17 22:41 UT7UA 14.097181 0 0 KO50ji 5 G0BON IO91qm 2188 286
2009-06-17 22:35 UT7UA 14.097182 0 0 KO50ji 5 G0BON IO91qm 2188 286
2009-06-17 22:35 AI4RY 14.097121 -20 1 EM72go 5 G0BON IO91qm 6897 45
2009-06-17 22:35 DF6MK 14.097105 -9 -1 JN68ik 5 G0BON IO91qm 1011 295
2009-06-17 22:33 W3PM 14.097158 -20 0 EM64or 5 G0BON IO91qm 6817 45
2009-06-17 22:25 IQ4DJ 14.097085 -9 0 JN54ks 0.05 G0BON IO91qm 1134 316
2009-06-17 22:02 G8IHT 10.140122 -19 -2 IO94gi 10 G0BON IO91qm 320 170
2009-06-17 22:00 IQ4DJ 10.140186 +5 0 JN54ks 1 G0BON IO91qm 1134 316
2009-06-17 21:58 IQ4DJ 10.140187 -4 0 JN54ks 0.05 G0BON IO91qm 1134 316
2009-06-17 21:56 IQ4DJ 10.140188 +6 0 JN54ks 1 G0BON IO91qm 1134 316
2009-06-17 21:54 OE1IFM 10.140273 -9 -1 JN88df 1 G0BON IO91qm 1263 293
2009-06-17 21:54 IQ4DJ 10.140188 -3 -1 JN54ks 0.05 G0BON IO91qm 1134 316
2009-06-17 21:38 OE1IFM 10.140166 -6 0 JN88df 1 G0BON IO91qm 1263 293
2009-06-17 21:18 IQ4DJ 10.140206 -15 -1 JN54ks 0.05 G0BON IO91qm 1134 316
2009-06-17 21:16 IQ4DJ 10.140207 -4 0 JN54ks 1 G0BON IO91qm 1134 316
2009-06-17 21:16 G7NKS 10.140137 -22 -1 IO92ub 10 G0BON IO91qm 64 201
2009-06-17 21:14 IQ4DJ 10.140208 -14 0 JN54ks 0.05 G0BON IO91qm 1134 316
2009-06-17 21:12 IV3DXW 10.140265 +1 -1 JN65qq 2 G0BON IO91qm 1214 307
2009-06-17 21:12 IQ4DJ 10.140210 -6 -1 JN54ks 1 G0BON IO91qm 1134 316
2009-06-17 21:12 G3NIC 10.140199 -23 -1 IO93rg 5 G0BON IO91qm 195 182

Wednesday, 15 October 2008

2N2-40+ Manhatten Contructon 40M TXCR

Have just completed a 40mtr (7Mhz) superhet transceiver, the design is based on commonly found PN2222 transistors. The radio features:
RF Gain Control
IF Filter bandwidth Adjustment
RIT
AF Gain Control


Picture Showing the 2N2-40+ Transceiver
(On top is a homebrew Stockton (SWR) Power meter)


The receiver has excellent sensitivity with narrow bandpass filters in the front end preceding a "Norton" designed low noise RF amplifier then a double balanced mixer using 1N4148's which mixes the input signal (7Mhz) with a 2Mhz from the VFO (Variable Frequency oscillator). The mixed product is then sent on to a 3 Pole variable bandwidth crystal stage of 4.915MHz.

The TX output power is 2 Watts QRP, using three paralleled 2n2222 transistors.

I have only given a brief flavour of the radio. For more information with detailed specifications see the designers web page of Jim Kortge, K8IQY.

On the web page you will also find useful information on Manhattan construction techniques and useful homebrew test instrumentation.

Jim has given me valuable support in sorting out problems that may be encountered in construction and was certainly an inspiration to me in getting this Project working. There is also a Yahoo 2n2-40 website for the 2n2-XXXX versions where a wealth of information can be sourced for fault finding and help on building the radio.

Monday, 14 July 2008

G8PG 10FT AERIAL

I built this aerial after seeing it on the G-QRP listing, I built this up fairly quickly over the weekend. Once erected in the bedroom I quickly made contact on 20 mtrs with OJ0/G3SXW on the first call.
Its not going to be a fantastic DX aerial but will allow me to contact most of Europe and also to take this on Holiday with me and try /P operation
Construction of the aerial can be fond here. http://www.io.com/~n5fc/notebk_ant.htm

DDS VFO


This is a DDS VFO based on Curtis Preuss, WB2V design from the July '97 Issue of QEX.
See http://www.qsl.net/yo5ofh/projects/dds_vfo_by_n2apb/dds_vfo.htm

I wanted a stable signal source for measuring quartz crystals for use in a filter circuit. I have an old 'Boatancher' valve Advance instruments signal generator but drifts too much, certainly inadequate for measuring crystals.

The circuit board was purchased from Far circuits. http://www.farcircuits.net. I have found that this site supplies a vast amount of PCB for most of the popular QRP circuits from magazines and club Journals such as QST, QEX.
W1FB's notebook etc.

The PCB were reasonably priced, and the P+P to DX locations was good too.

At the heart of the DDS VFO is an Analogue Devices AD9850, a 28 lead SSOP surface mount chip, with the frequency being controlled from a 16f628 PIC IC. An Etched PCB is highly recommended to aid soldering. In fact this was my first attempt at surface mount soldering. To solder the AD9850 it was best to align the IC on to the PCB tracks and first tack the corner pins down with a bit of solder, this allows fine alignment to be made before the IC is soldered permanently. Then when you are happy with the alignment solder all the pins on each side. Don't worry about solder bridges because these can be removed with some solder wick.

It was the first time I used solder wick and was quite impressed that in some applications is better than a de-Soldering pump. but for surface mount applications is a must.

The version I made used the Siggen 3C software developed by Bruce AA0ED and Craig AA0ZZ. The software can be downloaded from the files section in the DDS VFO Yahoo group website.
http://groups.yahoo.com/group/dds-vfo/

This version has.
Variable rate tuning based on the speed on which the shaft encoder is turned.
Band Memories to cycle around the ham bands.
Calibrate Mode if an external button is pressed on power up.
The popular 16f628 PIC IC, earlier versions had the 16f84 PIC IC.

I found that optical shaft encoder were very expensive to buy so I decided to homebrew my own using a modified potentiometer and the IR transmitters and detectors from an old ball type computer mouse. This worked extremely well, all the encoder parts are mounted 'ugly style' on a piece of copper clad board on the back of the modified potentiometer.
Follow this link for details of the optical encoder I used:
http://users.on.net/~merrifield/opto/index.html





The DDS VFO as it stands gives an output of 250mV. I added an amplifier board to give about 1Vpk-pk. The amplifier board was copied from the IQ-PRO circuit from the DDS VFO website link given above.