If you have ever tried transmitting on HF from a tall block of apartments, where it’s just not possible to erect a substantial aerial system, then this article is for YOU!
The limitations imposed are not so much that of limited space (although this can be a problem) but strict Rules and Regulations that prevent the erection of any beam or vertical rod aerial.
However, the very fact that the signal is going to leap into space from a good height above ground can be, in certain respects, a bonus, so all is not lost.
It IS possible to install an aerial…a wire aerial and using low power to enjoy some interesting contacts. The satisfaction of making contacts can be most rewarding.
What we need to do is be a little sneaky here. By this, I mean that we should just fit a length of wire, discreetly, tune it up and have a go! Perhaps you have already discovered or learned from others that applying in the normal way for permission will, almost certainly, result in the request being denied.
Let us now consider a few things obvious to some but which may have never occurred to others. A thin gauge wire against a pebble-dashed or concrete building, when fairly high above ground, will go virtually un-noticed, providing it is fixed into position quietly, during darkness and does NOT cause any flickering of neighbours’ television screens while they are watching Coronation Street!
The key factor in NOT giving any interference is in using an ATU (Antenna Tuning Unit) AND a Low Pass Filter which should allow low HF (High Frequency) signals to pass through, as we want these to radiate, but should suppress any VHF or UHF (Very High Frequency and Ultra High Frequency) signals or harmonics from the lower frequencies which could cause interference to television reception. One of the Golden Rules in determining this is that should you be giving yourself any flickering on any television channel then you can be fairly certain that a neighbour is also getting it and that is not acceptable!
Keep it simple!
A true Long-wire would be several full wave-lengths at the operating frequency. Such an arrangement is impractical for our requirements and in any case would fire straight off the end heading into space or down to the ground! What we are seeking is to send out a lobe that covers an area of the planet likely to include other radio amateurs.
Ideally, we should use a length of wire that is at least a quarter wave-length long, but preferably longer, at the lowest frequency we wish to operate on. This would mean a wire at least 130 feet long for Top Band or 1.8 MHz, but in practice I suggest that you aim for a length of 90 feet or as much as you can reasonably get away with.
As shown in the diagrams, #12 or #14 gauge wire is suitable because it will be strong enough yet hardly be visible. Stranded wire is preferable to hard drawn (solid) copper wire as it is more flexible and resistant to fracture from movement in the wind.
The Vertical will radiate the best pattern, so this would be my first choice.
If you have access to the roof, with the help of your wife or friend, lower a length of twine or strong nylon fishing line down to the point where someone is able to grab hold of it and pull slack into the room or balcony. Now join this line to an end of your wire. If using nylon line which is slippery, tie a knot using several turns and tape around the end to stop it from slipping and becoming free!
Once the end of your wire has been pulled up and your assistant has grabbed hold of it, go up to the roof and get the end fixed into position as soon as you can. This may involve some leaning over, so don’t attempt this if you are nervous of heights and if you do attempt this TAKE GREAT CARE!
You need a strong support point which in turn will invariably require the screwing in to the masonry of a hook, screw or masonry nail. Any of these is going to require either a short burst with a masonry drill (battery operated portable drill) or several taps from a hammer. I would prefer the drill myself. (If it were me doing this, I would be inclined to do this fixing one night and then wait several nights before pulling up the wire and attaching it to this fixing). I would feel inclined to attach a wrist strap to any drill, hammer or tools used for this task rather than risk an item slipping from my grip and dropping. TAKE THE GREATEST CARE!
The observant among you will have noticed that in the diagram, I suggest the use of “Blue Tack” to keep the wire away from the actual structure and stop it flapping about. This should only be a temporary step until you are satisfied that this can work for you. The best method of support is to use TV stand-off insulators at the far end (top) of the wire and two or three along the length. I appreciate that this might not be possible unless you are friendly with the dwellers in apartments between yours and the roof. Before fitting anything permanent though, I would want to make sure my aerial is going to work, so a cable-tie from wire end (small loop) to the fixing screw/eye will be fine for tests.
If there is a drainpipe running down the building and close to your apartment, you might want to consider passing your wire through a length of thin plastic pipe and secure this to the drainpipe where, if it is the same colour, it will look like part of it. Keep an eye out though for maintenance workers and if you see one showing more than a passing interest in your pipe, offer him a cup of tea and biscuits and explain your dilemma…he’ll probably wink at you and say no more!
There are no hard and fast rules regarding working out length except as said earlier, this wire should be longer than a quarter wave-length at the lowest operating frequency. Use this formula to work out how long your wire needs to be at the lowest quarter wave frequency:
L (length) = 234/F (frequency in MHz)
/ = Divide
As an example, suppose you wish to operate the wire at 14,250 KHz (14.25 MHz).
Length = 234 / 14.25 = 16.42 or 16feet 3 and a half inches. (Approx)
Because your wire will be end-fed, it is going to have high impedance so you will need a tuner and SWR meter between the end of the wire and your transceiver.
See the diagram for details of how to make a simple tuning device that should tune up any random length of end fed wire. Using low power, say 5 watts or less, then any tuning condenser which has vanes, removed from an AM Wireless, will do the trick. Just remember that the wider the gap between vanes, the higher the power it will handle.
For the variable inductance, if you can find a “roller-coaster” at a Radio Rally, that would be ideal. Failing that, make a former about 2 inches diameter (kitchen roll core?) and around 6 or 7 inches long (why doesn’t this guy use metric?) and use #14 gauge or thicker.
Wrap your wire around the former with a gap of a sixteenth or eighth of an inch between turns. When using the finished coil, a short lead with crocodile clip (as shown in diagram) can be used to change contact from one part of the coil (inductor) to another. Experiment with different combinations of coil coupling and tuning capacitor settings. Make a written note of which settings give best match for given frequencies.
NEVER MAKE ADJUSTMENTS OR COME INTO CONTACT WITH THESE PARTS WHILE TRANSMITTING RF!
I knew a Radio Amateur who lived in a tall block of flats not far from where I live. He tried many frequencies but found he could achieve excellent results from the 40 Metre band. This was the band he used until he became Silent Key. He found he could have regular contact with UK stations and European neighbours during the day time. In the evenings and particularly in the early morning (0100+) he could work DX and had confirmed contacts from as far away as Tierra Del Fuega which is down by Cape Horn at the tip of South America. Eric accepted his lot and was happy to be able to work anything at all. His aerial was a wire around his living room skirting board under the carpet! He used CW and less than a couple of Watts for all his contacts!
Choosing which of these two aerial methods to use will depend on how high in the apartment block you live. You could try both of them. The simplicity of this second way is that you can easily lower your wire, with a small canvas bag of sand as a weight at the bottom. This will keep your wire straight while you are lowering it and also keep the wire from swinging too and fro once it’s in the final position. You could also use a section of broom handle or similar with a V notch cut in one end to keep your wire away from the building structure. If you feel particularly paranoid, you can lower this when it gets dark, use it, then bring it back up before going to bed.
There is not much else for me to tell you, but I always get a feeling I may have forgotten something!
Ah, just remembered…should you fail to achieve a low SWR (standing wave reflection) no matter what you do, you may wish to consider using a counterpoise. This is, in effect, the second part of a half wave dipole so if you want to give it a try, cut a length of wire equal to the length of your main aerial. Connect it to the Earth/Ground side of your tuner and spread the wire along the corridor and under carpets in your apartment. This can be insulated and can improve your signal considerably. What it does is provide the simulated ground which is missing because you are living so far above it!
As with my previous article, readers must be prepared to solve their own problems. There are plenty of books in the Library or at your local Radio Club that will give additional information on these and other designs. I do NOT pretend to be an “authority” on the subject, so please just accept these humble offerings as an incentive for you to try things out for yourself.
You must also take responsibility for your own actions as neither myself, the Website Author should be deemed responsible for any use or misuse of this information or for being the cause of any adverse circumstance!
Si fallatis officium, quaestor infitias eat se quicquam scire de factis vestries
(If you fail, the secretary will disavow all knowledge of your activities)