In June 2009 Ireland joined a growing number of countries permitted to operate on a small portion of the medium wave band, just below the commercial broadcast segment, in the range 501 - 504 kHz. Several stations were granted permission and operations commenced. As has been documented elsewhere many stations have been worked, both in band and cross band, at home and abroad, ranging from Continental Europe, across the Atlantic to the USA and Canada and down to the southern end of Ukraine and finally up to Iceland Norway, Sweden and Finland and also being heard in Moscow.
A notable feature of this band is the steady, reliable nature of groundwave coverage and with this in mind I recently availed of the facility whereby Portable operations can take place.
Comreg, together with the IRTS and the individual involved, require that each event is applied for, giving relevant dates, location, contact details, hours of operation and the power of the transmitter being used.
In the period leading up to all this it was necessary to build and test a viable portable Station, based on the use of my Berlingo van. A 30 foot part of a 40 foot Spiderbeam Fiberglass pole was used with a simple round wooden peg to secure the Tee wire antenna, which was fabricated from twin twisted multistrand speaker wire. The vertical using both, the rest pulled apart and forming the two horizontal legs.
A 100 metre roll of 1.5 mm insulated earthing wire was cut into 16 lengths to provide radial wires, with lugs soldered to one end and a bonding bolt used to secure a single point for the radial kit. The far ends had a small loop formed and insulating tape sealed and secured them. The loop providing an eye for small L shaped stiff wire, fashioned from discarded coat hangers, an ideal and cheap way to hold the ends of the radials wire in place, in the ground, when deployed.
To secure the antenna support to the van, I refer you to the excellent idea described by John EI7BA, on his web page, for a ball hitch connection.
Using this superb idea, I got the welder out and made one for myself. It worked perfectly.
I now had the support, the wire antenna, with a ballpark figure for what might resonate, and the radial kit. I needed a dedicated Antenna tuning unit. An old variometer and two extra fixed multitap coils were selected. A home made 1 amp ammeter and SWR twin meter unit completed the fit out. These were all assembled on a base with a handle on the top, making it easy to move around whilst out and about.
The main antenna for 500 kHz was disconnected, left floating, and the van set up with all this gear, but no transmitter. Instead my little antenna bridge, running off a 9-volt battery, provided the necessary signal to start testing for basic resonance.
Whether from sheer good luck or some sub-conscious input, resonance fell within the range of the variometer with only one of the two extra coils in circuit. The relative height and length also play a part in the range of resonance secured. Matching to 50 ohms was then optimized by selecting 4700 pf Mica capacitors using those Croc Clip links. The available values range from 1 nF to 14 nF.
I have a selection of 500 kHz transmitters, two of which are to the design of Roger GW3UEP, who lives 8 miles inland from the coast, in West Wales. His 500 kHz web site is well worth checking out, containing plans for versions of his 500 kHz transmitters, test equipment, pictures and recordings of 500 kHz activities.
One of these was used to put some RF into this first portable style installation, and by arrangement, Roger listened and heard my signal. We delightedly completed a short contact, with my transmitter running just 10 watts. Things were looking good.
One of the very valuable things about portable operations stems from the need to bring together several elements to secure a working radio station, without the usual backup we enjoy from home. Planning is essential. Doing a dry run, i.e. actually physically building the intended station, then notating all the gear required. Making a list. Providing backup items, particularly those that which if broken, lost or whatever, would render the whole radio station non-viable. This also extends to the operator of the equipment. Will you be warm, or cool enough, have shade, food, water, are you rested enough? Always be prepared to abandon the project if safety is compromised, for whatever reason.
Now that I had a viable portable station for 500 kHz working, it was time to head off and test both the equipment and myself in the real World, but at this stage without any live transmissions taking place.
Several sites were chosen; particular emphasis was placed on remote sites, i.e. high up on mountains, or near the sea. All sites worked very well, but those by the sea proved really excellent. Reception of NDB’s, Non Directional Beacons, providing a ready supply of medium to low frequency signals for range testing. I was now itching to “have a go” out in the wilds, on 500 kHz.
Using the method required by Comreg, an application was made for several sites, on specific days.
In early June I loaded up the van with all the gear and headed off for the mountain above Redcastle, County Donegal. Using a narrow track and climbing higher, to about 270 meters a place was found leading to an old quarry. It had started to rain. Typical. By the time I had erected the support pole, pulled out the top hat wires and secured them using small nylon line and deployed the radial wires around and below the vertical drop wire, my trouser ends were very wet. Plugging in the 12-volt supply, the receiver was very quickly perked up, using the variometer. The Morse key connected to the QTX transmitter and the transmit / receiver switch flicked over. Time to get some RF flowing in the antenna.
Sure enough, on key down, the antenna current meter shot right up to 400 mA, but the SWR match was not exactly perfect.
Time to work those Croc Clips and start selecting shunt capacitors to find the perfect match.
Soon I had that sorted to my satisfaction, Antenna current was now up to 550 mA and a quick return to receive showed that
Roger, GW3UEP was already tuned up on frequency.
GW3UEP DE EI0CF / P HW K He came back straight away.
Oh joy! We were on the air on 500, in a remote mountain area, the top of my antenna almost tipping the clouds, as they swept past.
Standing at the back door of the van, open to the elements, the tips of my fingers reaching for the knob of my very favourite old Amplidan morse key, snug beside the other bits and pieces of equipment on the van floor.
My logbook, with its pages flapping back and forward in the wind soon had the first 500 kHz portable contact details documented. A full hour later, solid steady signals continued, at a distance of 250 miles, proving just how good groundwave signals can be, we terminated our communications from a remote portable location, happy with the results.
Within 12 minutes I had dismantled the station and was on my way to Moville and a strong cup of coffee at the café on the towns main street. Several other Portable operations have taken place. A number have also occurred at my home location.
We live right beside the sea; high tides lap up on to the salt marsh, which is part of the property.
Driving a single earth rod into the sea shore to a depth of 1 metre and without using the radials, just a single wire between the rod
and the ATU earth, the 1 amp RF meter had its meter needle slamming against the end stop. Lots of antenna current for 15 watts transmitter output power. Those same 15 watts only providing, at best, 550 mA, whilst up on the mountain sites.
Finally, it was thought productive to try a Kite supported antenna from the seashore portable set up. Winds on the day selected seemed strong enough to enable my Delta shape Kite to head aloft with a flying line and antenna wire attached. The Berlingo van was driven down on shore, everything connected and tuned up. All was well, or was it?
The receiver now seemed quite dead, no band noise, no antenna current on transmit. Looking skywards I could see nothing. My eye followed the antenna wire heading for deeper water. Then I saw it, the Kite had plunged into the sea. The following 30 minutes entailed untangling loads of seaweed. Line wrapped around rocks, barnacles, everything imaginable. What a mess! I almost gave up, but knew that Roger would be coming up on frequency, on sked, in about 15 minutes.
Eventually I managed to get the kite skywards again. By now the wind was acting more unpredictably. I established contact with Roger and he immediately gave me an S 7 report for my 15 watts. This equated to the report I would get from my main station antenna running 100 watts. My single ground rod and 150 feet of wire were doing the business. We carried on our contact, but what remained became a battle of wits with a kite constantly diving down and soaring up again. Several times the antenna wire was in part lying on the sea shore, antenna current way down to 200 mA or lower. My left hand on Variometer tuning knob, tweaking the setting, as best as possible, then pulling in the slack to keep the antenna wire off the ground, then feeding it out again to a misbehaving kite. Keying away in morse with my right hand, keeping Roger informed, updated so he could understand why my signal was changing both in pitch (sudden antenna mis-match conditions) and signal strength.
Luckily he was also making a recording, which proved later to be a fascinating record of a difficult portable antenna and station operation.
It’s remarkable how tolerant, despite the wildly changing antenna conditions, the system actually was, in practice. Communicationswere maintained despite all these negative factors, despite severely decreased radiated power at times.
Several other tests were conducted within these experiments which would have been almost impossible to conduct without the
challenges thrown up by the these portable operations. To my mind the 501 – 504 kHz band exhibit a distinct advantage for enhanced ground wave coverage over that available to higher frequencies.
Relatively simple equipment deployable in remote locations and / or without the availability of grid power would provide a solid backbone link or network, in times of emergency. Transmitter power output was kept deliberately low to ensure that a higher ERP would not mask any possible weakness in the system. I am happy to conclude that Medium Frequency CW proved it’s worth once again. Already I have further plans to test smaller, more compact portable antenna and earthing systems in more remote locations.
Finbar O’Connor EI0CF Malin, County Donegal.