New antenna for 80 metres goes up

Surprisingly, the weather recently has been suitable for me to work on antennas. So even this late in the year I had an opportunity, not to be missed, to erect a new antenna for the 80m band; a base-loaded vertical wire element supported by a Spiderbeam heavy duty 12m long telescopic fibre-glass pole. The pictures show the antenna base with loading and matching coil inside the storage container, and the antenna's location.
I have just made my first contact on the 80m band using this antenna with a radio amateur in southern Spain, 2463kms away. My transmitter output power was only 35 watts. The antenna's performance could be worse !

Improved phasing exciter

I have completed some improvements to the single-sideband phasing exciter, ( post 25 January 2010 ), for my longwave transmitter, just in time for use during the good propagation conditions on the 2190m band over the winter.
The passive phase shift network was not producing accurate 0 and 90 degree phase shifted AF. In fact it was well outside specification; perhaps not surprising as I bought it in 1978. So I replaced it with an active circuit based on a dual op-amp. I optimised the unwanted ( lower ) sideband suppression at 800Hz. There is little point anyway in achieving exact quadrature audio channels over the entire speech band as the modes in use on longwave are extremely narrow-band.
I added a tuned class-A post-mixer transistor amplifier stage.
Upper sideband is now selected automatically as I have disabled the sideband switching facility; until such time when I see a lower sideband signal on the band.
The top picture is my signal, received on 137.7KHz, from just the exciter sitting on the workbench, ( lower pic ), when transmitting using chirped multi-tone Hellschreiber mode. As can be seen, the signal occupies only about 5Hz of band !

PC-to-PIC serial comms

I have been programming the EUSART module of a Microchip PIC18F4550 microcontroller on my MYDEV2 development board for RS-232 serial  communications with a pc running a terminal application; in my case 'HyperTerminal'. I have configured the connection for 1200 baud asynchronous operation. Although this is one of the slowest of the standard com port baud rates, however in conjunction with the 8MHz PIC clock it gives the lowest baud rate error of only 0.1%.

The connection is called PC-PIC_EUSART. Pressing any key 'wakes up' the EUSART and starts the sequence. The above capture of the Hyperterminal screen shows, for example, the steps taken to change the dfcw dot-dash frequency shift to 4Hz. All seems to be error-free !

Now that I have the connection working, I am considering incorporating serial comms functionality into my PIC controlled frequency synthesiser, so that values, e.g., relating to priority band and dfcw shift, which are held in PIC data eeprom, can be changed quickly in real time without having to modify, build and reload the entire source code file.

PC-to-transceiver audio interface

Sometimes there are quick and easy construction projects on my long 'to do' list, e.g., a pc sound-system to transceiver interface. I have one already, ( just visible in the picture posted on 14th July 2012 ); but with the arrival in the shack of pc number 5 another interface would be convenient. The existing one incorporates transceiver mic switching, mic gain and speaker. The one I have just completed is basic, containing only the bare essentials of the two line isolation transformers.
The transformers provide the path for audio without allowing any dc connection which is the preferable situation when connecting together these two valuable pieces of equipment; radio transceiver and computer.
I obtain these transformers from discarded telephones and modem cards. Using temporary connections, the windings and taps which give the best results on both transmit and receive can be identified. In the finished interface the transformers are orientated for minimum interaction.
Currently I have two spare transformers, sufficient for another interface; one from a telephone, and the other yet to be removed from a modem.

Trap and match

I have completed the 'L-match' network and re-checked the resonant frequency of the trap, 1821KHz; both are now ready to be installed with the new antenna, ( last posting ).
I made a very important improvement to the water-proofing of the original trap, ( posting dated 8th April 2010 ), by fitting end-caps. These are translucent polythene and originally the tops from curry paste jars. I was delighted to discover that they are a tight clip-on fit on the 90mm diameter former. I had carried out beforehand the traditional microwave-oven loss test on the material which passed. I will now look for similar jar tops for my other coax traps.
I must hurry to finish the antenna as a Canadian radio amateur is eager to contact me on the 160m band.

Straight up

Today I finished installing the vertical section of a new 'trapped inverted-L' antenna for the 160 metre and 2190 metre bands to the final height of 17.8m. It is constructed from 4m lengths of aluminium tubes of various diameters giving it a taper from 45mm diameter at the base to 26mm at the top.
I have been making ground-mounted vertical antenna elements for low frequencies for many years and in my experience 18 metres is about the maximum height for this form of construction using light material, as well as being at the limit of what one person can erect. Higher than this and the construction can quickly become uncontrollable during lifting, resulting in disaster. However, I still have about 2m in reserve should I feel bold enough one day to try to increase the height still further.
Prior to erecting the vertical part, I had already connected a 15.8m top wire. I now have to fit the trap and an additional 15m of wire to an anchor point on a 12m pole about 30m away.
The storage box just visible at the antenna base will contain the L-type 'L-C' matching network to 50 Ohm coax cable feedline for operation on the 160m band.
Thunderstorms are forecast here tomorrow; an early survival test !

Two generations

The early MKI ( lower ) and very recent MKII ( upper ) embedded control frequency synthesisers are both resting on top of my longwave transmitter. I will interface the MKII with the transmitter as that was always one of my intended applications. The MKI will now be used as an item of test equipment on the workbench to provide an lf signal source.

Poland now on the 4 metre band

A new band, 70.1 - 70.3MHz, was officially released to radio amateurs in Poland at 00:00CET today. I have been prepared for this moment for the last 5 years, and was ready and waiting. I made radio contacts using morse code, voice and data; the latter being in FSK441 mode using meteor-scatter with Enrico, callsign IK0BZY, in Italy at a distance of 1295 kms, as can be seen in the partial screen capture from WSJT9.

Keypad handler

Today I finished writing the PIC code in 'C' language for handling the operation of a typical matrix keypad, as mentioned in the previous posting. Characters 0-9, *, # can be keyed-in and displayed one at a time.
The purpose of this activity is to pave the way towards my ultimate goal which is to enter frequency tuning data via a keypad instead of a rotary encoder, in an alternative version of the embedded control frequency synthesiser. At this later stage, the * and # buttons will be assigned to 'clear/backspace' and 'enter'.
For now, however, further development has to be put on-hold.

Gradually moving forward

Having a lot of spare time recently has enabled me to progress with some unfinished PIC MCU related activities. For the first time I have been writing code in 'C' language and programming PIC MCUs using Microchip's MPLABX IDE and ICD3. So far I can write characters to a display, and also detect when any button on a particular row of a keypad has been pushed; all quite encouraging. But I still have much more programming to do in order to complete even the quite basic operation of keying-in and displaying numerical data.
I have also been experimenting with software, ( assembly language in this case ), to detect disconnecting the power source from a PIC microcontroller, ( PIC18LF4455 ). A variable low voltage power supply would be very useful here.
And finally, from a most unexpected source, I have obtained cut and engraved black plexi front and rear panels for the frequency synthesiser enclosure.

MyDev2 enhanced

Schematic - note Vcc connection depends on usb-powered or self-powered application

I have upgraded to version 3 my PIC MCU development platform, MyDev2, ( first posted on November 2nd, 2010 ), with the addition of pull-down resistors R25-R28 for the keypad rows connections now that I have decided on the method I will use in coding the operation of the keypad and the interfacing required to the microcontroller. I have already started writing the code in 'C' programming language, instead of the 'Assembly' language which I have used for all my PIC projects until now. The keypad will be a 'telephone' style 4 row x 3 column, 0-9, # and * type.
I have also fitted a new microcontroller type, Microchip part PIC18LF4455-I/P, which, as well as being a few cents cheaper than the original PIC18F4550 and PIC18F4685, has an extended operating voltage range, ( denoted by the 'L' in the part number ), down to +2V, as I want to experiment with coding the detection of switching off the power !

New antenna radiates

The new antenna for longwave, mentioned last time, radiates. I have been making some test transmissions on 137.7KHz and these transmissions have been received by Jacek, callsign SQ5BPF, on the other side of Warsaw. The screen capture below shows how he saw my signal on his 'lf grabber'. Incidentally, he could also hear it.
So now I have a reference signal with which to compare future signals as I make improvements to the antenna installation; the aim being to make the signal stronger and the signal trace white rather than the orange colour it is now. Losses in the system have to be reduced. To achieve this, I shall start by burying more copper in the garden. This will be a very labour intensive and time consuming activity. I shall probably be eaten alive by mosquitos before completion ! I hope to report total success in the near future - if I survive the ordeal.

Wire in the sky

I have erected a new antenna in readiness for the restart of my radio activity on the 136KHz 2190m longwave band during the coming autumn and winter season; simply a 45.9m long wire, and a number of bare copper conductors buried in the ground directly below. The wire is supported at the mid point by a fibreglass pole, and a spring counter-weight ( see inset ) running through a pulley tied at the highest point I could reach to a tree at the far end.
The (in)famous loading coil, ( posts dated Feb 19th & Sept 13th 2010 ), will still have to be pressed into service; but fortunately it will be installed inside my radio room. What a huge relief that I will no longer have to use the coil outdoors or carry out frequent maintenance on it inspite of the snow and ice, as with the previous antenna !
My last attempt to put up a different antenna for long wave was in 2009. It was a much more complex design, both electrically and mechanically, requiring 'miles' of wire. It would have been an excellent performer. Sadly it never came to fruition, being blown down / away four times during summer thunder storms before I had even finished building it. There was an important lesson to be learnt from that ! It's better to have a simple antenna than no antenna.
While the performance of the new antenna will be inferior to the one I didn't complete, it should out-perform the last operational one.

Then there were four

From time to time since the last post, ( 16 June ), I have been populating three more circuit boards; four are now complete. This is not quite the rate of 3 per week which should be achievable, single-handed; what an efficient production line that would be !
During this activity my soldering skills working with surface mount components, some minute, have quickly improved. Surprisingly, I didn't find the 44 pin microcontroller chip to be the most difficult to mount.
Now I will progress further with the case. I have already finished the technical drawings for the top, base, front and rear panels ready for their fabrication. And today a local firm precisely cut the extruded, anodised aluminium sides to the final length.

Densely populated

A new batch of Analog Devices synthesiser chips has arrived, enabling me to finish populating one circuit board with components. I programmed the PIC MCU via the bootloader with my latest v2.00 code and, after powering up the board, all seems to be working fine.

BF991 receiver RF preamplifier completed

While waiting for the boardhouse to make the printed circuit boards for my frequency synthesiser, ( see post on Mar 8, 2011 ), I reckoned I should have just enough time at long last to build the low noise 144MHz receiver RF preamplifier which I designed months ago, ( see post on June 16, 2010 for circuit schematic ).  For this piece of equipment I again made the pcb; the artwork for it is shown, ( actual size 4.2" x 2.2" ).
I built the circuit on single-sided copper laminated fibre-glass board, all components being mounted on the same side as the tracks and copper ground-plane; in effect surface mount technology even though only the BF991 mosfet, in a SOT143 package, is actually a surface mount device. A piece of double-sided board material was soldered vertically across the circuit board to act as a screen to prevent coupling between the input and output tuned circuits. The preamplifier is housed in a Hammond "Eddystone line" type 27134PSLA die-cast metal enclosure, 111x60x31mm.
Being somewhat larger than a matchbox, it's not the tinyest rf preamplifier that I have ever seen. Small size is not an issue for me, as it will not be installed internally in any other equipment but used outdoors close to the antenna. Besides that, the heavy-duty change-over relays that will be necessary to divert the transmitted signal around the preamplifier will add significantly to the overall size anyway.
Achieving a low noise figure for the preamplifier is strongly dependent on the C-C-L input bandpass filter and matching circuit which should use low loss, ( i.e., high 'Q' ), components. I easily obtained some suitable ceramic trimmer capacitors for C1 and C2, but sadly no silver plated wire from which to make the coil L1 !

The art of pcb design

 

Coincidentally, the rotary encoders and Microchip microcontrollers for the current version of the frequency synthesiser project both came in the post today; one of each is required in each synthesiser. I had been waiting especially for the arrival of the encoders as I had to create that part in a new component library inside the CAD software so that I could complete the artwork for the track layout of the double-sided printed circuit board.
Microchip had protected the microcontrollers in a little plastic box, ( like a presentation box for jewellery, rings etc), lined with static dissipative foam. I must say that this level of care impressed me ! A pity, though, that both chips flew out when I opened the box for the first time.
An encoder and microcontroller will be in the positions of SW1 and IC1 respectively. For clarity, just for this posting, the picture of the pcb design, ( actual size 4.0" x 3.2" ), doesn't show the copper-fill for the ground-plane on the topside. I have made pcb's many times in the past for various projects; but this one will have to be manufactured commercially.
The encoder is an Alps part, type EC11B152420Q, ( having 30 positions and 15 pulses per revolution plus switch ), and the Microchip microcontroller is type 18F4550-I/PT, in a 44 pin thin quad flatpack (TQFP) plastic package.

Winter's icy grip

Cold air from Scandinavia brings freezing weather conditions to Poland with temperatures well below 0C. I recorded -16.5C overnight last night and -21C is forecast for tonight. Although today was clear and sunny the temperature was still only -10C to -12C. Sun illumination level was high today, making it possible to receive some nice images transmitted by the NOAA weather satellites. I received the one shown above from NOAA18 at 1131gmt on 137.9125MHz.

Bootloader in action

After programming a boot-vector and boot-block into the PIC microcontroller's flash program memory, I used a bootloader to upload my application code to the PIC from the PC using its com port, the level converter, ( featured yesterday ), and the EUSART, ( enhanced universal synchronous asynchronous receiver transmitter ), connections on the PIC. The top picture shows all the project hardware, looking a bit untidy by now.
To check, I read back from the PIC to the bootloader the entire contents of program memory, ( actually also data eeprom and config ). The screen capture in the lower picture shows just the first portion of this, from address 0000hex to address 00DFhex. On looking at this I can see that the bootloader has highlighted the boot-vector code, at address 0000hex - 0003hex; the high priority interrupt vector and low priority interrupt vector are still at 0008hex - 000Bhex, and 0018hex - 001Bhex respectively. My PIC type, com port and speed are correctly declared in the bottom right corner. I notice that the time taken for the flash memory 'read' was 35 seconds. I'll configure com2 for a higher speed to reduce this, although I won't be reading memory very often. I recall that, earlier, 'writing' took only 4 seconds.(*)
It'll be interesting to use the bootloader for programming instead of the ICD2, which of course will still be essential for debugging.
All this has got me thinking about the download area on my eventual (?) website !
( My thanks to Microchip Technology Inc. for the freeware serial bootloader AN1310v1.04 )

* Update, 11 February : I subsequently changed the speed of com2 from 9600 to 115200 bits per second; now write and read times have been reduced to 0.942 and 2.975 seconds respectively.

PC talks to PIC projects

Today I built a CMOS/TTL to RS-232 level converter using a Texas Instruments part, MAX232N, driver/receiver chip in a 16pin DIP package. Now, provided that the PIC is self-programmable, ( which indeed my PIC18F4550 is ), it will be possible to connect my PIC applications/firmware to a PC serial ( com ) port, or via a USB (*) adaptor.The purpose of this interface between PC and PIC is, ( after making a bootblock in the program memory ), to use a bootloader so that a PC can read, write, verify, modify etc the PIC's software; or software updates downloaded from the web can be installed by a user anywhere.
The schematic and track layout for a double-sided 2.1 x 1.6 inch circuit board show the MAX232 in a 16pin SOIC package.
(*) Although I am usually 'game' for a challenge, I have put on hold indefinately any of my attempts to make a USB interface.