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.