Stealth Amateur Radio
In 2001 I moved to a new house (or QTH in ham talk). Like most hams, I had in my mind
the dream of an isolated house with a large plot of land where I
could put up a big antenna and run high power without upsetting
any neighbours. 
However,
after a lot of thought it became clear that this desire was not
compatible with the type of house I wanted to live in. What I
wanted was a brand new house, within walking distance of the
centre of Cockermouth, the small town where I live. Like all new
houses in England today, this meant accepting a tiny plot with
barely enough room for a 20 metre dipole. In practice, it also
meant accepting a house with a restricted covenant that permitted
no ham radio antennas.
Though many hams might not agree, I accepted this restriction. One of my reasons was that not being prohibited from erecting an antenna doesn't necessarily mean you won't have problems if you do erect one. At my previous QTH I had erected a trapped vertical antenna in the garden. A few neighbours disliked it, and tried to get the council to make me apply for planning permission for it. The council accepted that it was small enough not to require permission. This was fine for me, but it didn't make me the most popular person in the road, and my life outside ham radio suffered a bit because of it.
One aspect that always seems to get overlooked in the arguments about hams having the right to put up antennas are the rights of non-hams to enjoy their environment witjout having to see ugly antennas. And antennas are an eyesore to most people. I can fully understand why non-hams in an attractive locality would prefer not to see large radio antennas in neighbouring gardens, and I don't wish to be the person who inflicts these eyesores upon them.
Because of this, I accepted the restriction on having no visible antennas. Rather than feeling I would have to give up the hobby in order to live where I wanted, I viewed it as a challenge. And I felt that by meeting this challenge, I might become an example to others who would like to become hams but feel they can't because they are unable to put up a big antenna.
There must be many potential radio amateurs who are put off the hobby by the thought that they will need to erect a large antenna that will upset the neighbours. Even the family may object. I heard of one ham whose wife refused to allow an aluminium monstrosity to be erected in the garden. The challenge I set myself was to see if it was possible to operate a HF amateur radio station with worthwhile results, without my neighbours knowing anything about it: a covert amateur radio station.
Antenna choices
I spent many hours researching the types of antenna that could be used indoors, or in the loft. There are many possibilities, but obtaining information about how well they work isn't easy. I could find no reports of some of the antennas advertised as for "stealth" operation, such as the controversial crossed field antennas. Most of these very small antennas aren't cheap, and I wasn't prepared to spend a big sum of money on what might turn out to be an expensive dummy load.
The most useful article I found was the Compact HF Antenna Roundup published by the ARRL in QST, March 1998. (If you're an ARRL member, you can get this from the ARRL Members Only website.) The MFJ Magnetic Loop got a good write-up, so I bought one.
MFJ-1782 Magnetic Loop
I bought the MFJ magnetic loop before I moved to my new QTH, so I was able to compare it with my old vertical. I was extremely impressed. Even indoors, it outperformed the vertical by a few dB on 10 metres. It became less effective as the frequency dropped, so by 20 metres it was a few dB down on the vertical. Nevertheless, for such a small antenna this is still an excellent result.
The version I got was the 10MHz - 30MHz model with the manual control box. The so-called automatic control box is a lot more expensive, isn't all that automatic, and you're paying for SWR and power metering that already exists in most transceivers. I found that brush noise from the motor that drives the tuning capacitor provides an effective noise source when tuning the antenna, so it was possible to tune it to almost spot-on just by ear. I could then "tweak" it for best SWR using the metering on the radio. Some reviewers on eHam.net have complained that this is too much effort. They want to be able to push one button and have the antenna tune itself. I think some of today's hams are spoilt and lazy. It's still easier to tune the MFJ loop than to tune a long wire using a manual ATU, as many people still do. And I'd rather do that than pay a lot more for a computerized control unit.
The MFJ magnetic loop would be my first choice recommendation for anyone who wants or needs to set up a covert ham radio station. It works fine indoors, but for best results you should position it as far as possible from walls and other objects. If you can't manage a permanent installation, you could mount it on a stand and keep it in a wardrobe or cupboard, bringing it out only when you want to use it. I know of no other antenna that is small enough to be used indoors and radiates such a potent signal.
The MFJ loop has two disadvantages, which nevertheless may not deter you given its good performance. It is such a high-Q antenna that you need to re-tune it even after changes of a few kHz in frequency. You need to tune it even if you only want to do some casual listening: the Q is so high that if the antenna isn't tuned close to the frequency of the receiver you won't hear anything. The other disadvantage is that the antenna is a solid, welded 3 foot hoop so you need a hole that big if you want to get it up in the loft. The access hatch to the loft in my new house is not that big, and would have required expensive carpentry work to make it large enough. Because of that, I used the MFJ loop for a few weeks inside my upstairs shack before deciding upon a different solution.
Quad Loop with remote autocoupler
Another approach that many hams claim to be effective is to use a horizontal loop of wire, broken at the middle of one side (or in a corner) and fed there. This is not a resonant antenna, so it will have a widely varying impedance at different frequencies. You should theoretically tune it using an ATU in the shack only if fed with open wire feeder. And you'll probably need something better than the auto-ATUs in most radios. If you want to keep things neat and tidy and feed it with 50 ohm co-ax you must place the matching unit at the antenna feedpoint. The easiest way to do this is using an autocoupler such as the SGC SG-239. This will also give you the benefit of instant tune-up, since the SGC autocoupler has a built-in computer.
I ran a heavy gauge wire (something like 6A rating) round the inside of the loft space using insulators at the four corners. The dimensions of the loop are about 4.8m x 5.5m. I placed the SGC autocoupler at the centre of one of the 4.8m sides, almost directly above the operating position. This is quite a small loop (modern English houses aren't big, unfortunately.) Comparing this with the MFJ magnetic loop, on the whole I think the MFJ loop was a slightly better performer. However, the ease of tune-up offered by the autocoupler, plus the fact that I was able to install the wire loop in the loft without surgery on the house tipped the balance in its favour.
Another benefit of the wire loop is that it isn't high-Q, so for general receiving it still works with the autocoupler switched out. This is very handy when you turn on the radio and want to have a quick listen around to see what activity is like. You only need to tune the loop if you want to transmit. The MFJ magnetic loop would need retuning every time you changed bands, even if you only wanted to listen.
The SGC-239 autocoupler tuned this loop on all amateur bands, right down to 160 metres. Again. this is an advantage over the MFJ magnetic loop, as that tunes down only to 30 metres. (MFJ makes a version that goes down to 40 metres, but you sacrifice 10 and 12 metres in order to do that.) Obviously, the wire loop is pretty inefficient on the lower frequencies, but so would be the magnetic loop. There just is no way to radiate a big signal on the low bands using a small antenna. I have never tried to make contacts on 80 or 160 metres. I've made only local contacts on 40 metres. But this small loop works incredibly well on 20 metres and up. I'm constantly amazed by how far my signal can get, considering that I'm running low power, to a small antenna, situated in the attic. Modelling the loop in EZNEC shows that it has some directivity, and even a bit of gain, on the higher bands.
Conventional wisdom says that it is better to mount a loop like this round the outside of the house, below the roof line. I didn't do this for a number of reasons. First, I don't have a ladder, so I can't get up there to do it. Second, the houses are so close together that you couldn't do this without it being visible to the neighbours, so it wouldn't meet my objectives. In fact, I'd have to ask one neighbour's permission to put the ladder on their land so as to reach one side of the house. Third, the shape of the roof isn't ideal to run a loop round it. And fourth, if I did this, the loop wire would be closer to the house structure than it is running inside the loft, which might de-tune it. Using an indoor antenna also allwed me to save money by using the non-weatherproof SG-239 autocoupler. The SWR does change a bit on wet days, so the wet roof probably affects efficiency a bit, but not enough to notice.
QRP Operation
Perhaps I'm being over-cautious, but I think that it's essential to use low power when using an indoor (or in-attic) antenna. I'm concerned about the physiological effects of radiation, but mostly I'm worried about EMC problems. I just don't believe that it's reasonable to expect phones, TVs, stereos and so on to have enough immunity to RF to remain interference-free when 100 watts is being radiated by an antenna inside the building. Even low power can cause problems. My transmissions blast through the computer speakers, and I found that even a couple of watts of RF on 15 metres interfered with the operation of the track-pad of one (now defunct) laptop. This resulted in a lost DX PSK31 QSO, the first time I discovered it! I solved both problems by using my desktop PC for ham radio data operation, which means that as the sound card is now dedicated to PSK use, the speakers are no longer connected anyway!
As far as on-air effectiveness is concerned, it's worth remembering that the difference between 100 watts and 5 watts is only two S-points, which is usually a lot less than the QSB at any given time. This means that the chances are if you can work someone using 100 watts you can work them using low power, but you may have to try a bit harder. My Elecraft K2 runs a good 10 watts plus on most bands, and it's highly effective speech processor means it's "talk power" is a lot closer to many 100 watt radios than you might think. There are times when I wished I had a kilowatt and a beam, but I've honestly never wished I had a 100 watts instead of just ten. It just doesn't make that much difference.
I think most of the difference between 10 and 100 watts is in the mind. To be content running low power to a small antenna you have to put yourself in the state of mind where you aren't concerned about the few contacts you can't make because you're just a bit too weak for the other hear you. Otherwise, you'll simply become frustrated. It's important, I think, to use a radio that can only run low power, such as my K2. If you have a radio that can run 100 watts, you'll constantly be tempted to turn up the power. And if you do that in a "stealth" situation you may find that you've blown your cover.
Modes like CW and PSK31 certainly help you make the most of low power. It's amazing how little power you need to make contacts using PSK31. I always wonder why some stations insist on running 40 or 50 watts. I have had rag-chew contacts with Stateside stations on PSK using just 4 watts. Who needs QRO and tons of aluminium?
The results speak for themselves. I don't spend a lot of time on the air, and I go on the air when I can find the time which does not always coincide with the best conditions. Nevertheless I have worked North and South America, Antarctica, Japan, South Africa and the Phillipines. The only continent I haven't yet worked is Australia. I think this demonstrates that it is possible to get enjoyment from the hobby running low power to an invisible, indoor antenna, and that ionospheric conditions play a bigger part in whether you can work anyone or not than any other factor.
Conclusion
My experience demonstrates that antenna restrictions are no reason for going off the air. You may never be a big signal working DX when conditions are poor, but there's a lot more to ham radio than working DX.
Contrary to popular opinion, you don't need high power and a big antenna to have fun on HF. It is possible to enjoy ham radio using low power and an indoor antenna. If you wanted to be a ham, but have been put off by the perceived need for unsightly antennas and worries about what the neighbours will think, my advice is to go for it. Get on the air using covert amateur radio!
Want to chat about stealth radio?
If this article has interested you, and you would like to chat about stealth radio operating and get more ideas, join the Stealth Amateur Radio message board at Zerobeat Forums. Ask questions and get advice from others in a similar situation. See you there!