Preamble
It was developed simply because of my own personal circumstances which meant I often had to play radio from restricted QTH's. My employment in discrete antennas sure helped me out, as not only did I have demanding customers for discrete antennas but I find myself missing amateur radio when operating from hotel rooms abroad or "digs" in the UK!
Of course I've done all the large antennas from home but it's too easy and I wanted to have a bit of a challenge from building COMPLETE indoor stations totally indoors and so the following has been in use for the past few years by myself almost daily.
The antenna is nothing more than a simple 2.4 metre square loop "drawing pinned" to the internal brick wall of the spare bedroom. Yep, thats right, the inside wall of the spare bedroom - ideal for flat dwellers, hotel rooms or whinging neighbours!
It is currently used with it's base height at 3m AGL.
The loop has a simple switched inductance at the top of the square loop and uses a simple coaxial stub to tune the antenna. An additional variable capacitor placed across the feedpoint can be used to fine tune the resonance of the antenna. The basic configuration is shown below.
At J1 or J2 the coaxial stub can be replaced by a good quality ATU, preferably one which doesn't use toroids!A balun is not required and at the most a simple choke style balun made from about 6 turns of coax and about 6 inches diameter can be used to attenuate radiation from the feeder cable. Good quality ATU's are expensive and often cost around 300 pounds sterling so to cut costs the simple coaxial stub can be use to utilise the self inductance and capacitance to from a tuned matching circuit to provide a 50ohm match to the amateur tranceiver. It is also possible to connect a variable capacitor at either the beginning or the end of the coaxial stub in order to provide across band fine tuning. The antenna is fed by simple 50 ohm coaxial line.
Here's the description of the antenna at various bands.
160m
Use 100uH inductance at the top.
A coaxial stub which is open ended RG58 style coax is 48cm long.
Open ended means just dangle a piece of coax at point J2 with braid to one side and centre to the other. The end is left "open" or with a simple variable capacitor for fine tuning. Results have been reasonable for local working but not amazing. Generally I qso 50 miles or so.
80m
Using ZERO inductance and a 139cm stub plus 5 watts I have made plenty of UK/EU qso's with this antenna. Obviously larger antennas are better but expect your signal to be about 2 s-points down from stations using full size antennas and assuming the same power output.
40m
Using 10 watts I have had some QSO's around the UK but I am not keen on this band so my experience is limited. Zero inductance and a 39cm stub is required.
30m
THIS BAND AND QRP IS BRILLIANT! 5 watts rarely fails to get a QSO. I have only operated in the daytime when I have had numerous QSO's around europe with just 5 watts with no hassle. Just use a 30cm stub and zero inductance.
20m
Numerous european and north american qso's made in the direction of radiation of a normal quad loop. Use 15uH of inductance for best results.
17m
Use a 3cm stub and zero inductance.
Numerous north americans, the middle east on 1 watt and Russian ragchews are easy.
Due to the radiation pattern of the antenna in my QTH I am best placed for north American and middle eastern QSO's.
15m
All over north america, the carribean and some south Americans with 10 watts.
1 watt to the Lebanon and recently my first call was answered by the 3B9C expedition using 25 watts of ssb. Countless europeans of 5w cw. North Americans worked by the truckload. Brazil also worked. Use zero inductance and 6cm of coaxial stub.
12m
Plenty of north americans and europeans. Use 9cm of RG58 stub and zero inductance for best results.
10m
Plenty of north American, the caribbean and the middle east as well as Europeans on 29MHz FM and I only used a max of 25 watts. Brazil also worked. Use 15cm of coaxial stub and zero inductance.
Remember the quad loop up on all these freqs is like a horizontal dipole and as such is directional.
HOWEVER we can perform a useful trick here - use 60uH of inductance and you can rotate the radiation in the opposite direction and with vertical polarisation! A rotatable indoor dipole without rotating it! This time you use 60uH of inductance at the top of the loop and approx 20cm of open ended coaxial stub.
I've worked gawd knows amounts of north americans, south americans, central americans, the middle east, europeans and Russia and south african stations with only 10-20 watts ssb.
Remember all of the above has taken place outside the sunspot maxima.
6m
In the summer sporadic E season it is typical to be able to work distance about 1500 miles. With only 5 watts cw/ssb I have had plenty of qso's at this distance with ease in the direction of the loop, which is in the same direction of a normal quad loop. I don't frequent 50Mhz all that often but it's pleasing to work exactly the same typical distances as every one else with this silly antenna!
NOTES
This antenna is like any other antenna - it's just a resonant circuit that radiates. The loop is the inductance and all you need to do is add the required capacitance to it to for a tuned and radiating circuit.
Rules of thumb are that the smaller the loop the more capacitance you need to resonate it. When tuning a coaxial stub you simply snip off 5mm at a time to provide the required match. Circumstances vary! So be prepared for slight differences to stub lengths etc. It is perfectly in order to have a reasonable variation in loop length and adjust sub length/variable capacitance in order to suit.
All polarisation is horizontal except for 160m where it is vertical OR on 28Mhz using 60uH inductance it also becomes vertical polarisation.
This antenna as described is in use by G0FTD every day and provides many happy hours of operating - so I know it works.
With the restrictions placed upon so many of us these days it really is pleasing to report a real antenna that allow just about anyone to play amateur radio with some sense of normality. Youngsters with parents can put up this antenna in their bedrooms, pensioners can (and have) used this antenna in retirement homes and restricted accommodation, students and flat dwellers can use it to at least continue their chosen hobby.
Noise is a big problem on receive and is often very restrictive. Sorry folks but it's a problem we ALL suffer from. Apart from operating at night when hopefully the local TV's have been turned off there's not a lot we can do.
CONCLUSION
Amateur radio IS possible under the most extreme circumstances so long as you don't expect all freqs to be 100% qrm free on recieve and that you'll have to expect your signal to be a few s-points lower. In practice it's not really a problem and then it pays to think that if your using a bit of "damp string" and a few watts your acheivement is damn good compared to all the sillywotsits who spent 1000's of euros/pounds/dollars and massive
effort for towers/kilowatt amps/expensive aluminium tubes to make yagi's blah blah.
It's all relative folks - so enjoy amateur radio under your own circumstances and stop feeling left out!
A BETTER LF ANTENNA.
I have also tried a 4.2m x 2.4m loop with excellent results on the LF bands. It seems to outperform the previous antenna on the LF bands by quite a large margin. The antenna is a corner fed loop as shown here.
I have NOT tried coaxial stubs with this antenna. I have only use an atu for matching at the point of J1. Never use an atu at the rig end!
However, I have used computer modelling to assist me attain a high degree of accuracy with the previous antenna, so here are the recommended starting points for using open ended coaxial RG58 stubs.
It was developed simply because of my own personal circumstances which meant I often had to play radio from restricted QTH's. My employment in discrete antennas sure helped me out, as not only did I have demanding customers for discrete antennas but I find myself missing amateur radio when operating from hotel rooms abroad or "digs" in the UK!
Of course I've done all the large antennas from home but it's too easy and I wanted to have a bit of a challenge from building COMPLETE indoor stations totally indoors and so the following has been in use for the past few years by myself almost daily.
The antenna is nothing more than a simple 2.4 metre square loop "drawing pinned" to the internal brick wall of the spare bedroom. Yep, thats right, the inside wall of the spare bedroom - ideal for flat dwellers, hotel rooms or whinging neighbours!
It is currently used with it's base height at 3m AGL.
The loop has a simple switched inductance at the top of the square loop and uses a simple coaxial stub to tune the antenna. An additional variable capacitor placed across the feedpoint can be used to fine tune the resonance of the antenna. The basic configuration is shown below.
At J1 or J2 the coaxial stub can be replaced by a good quality ATU, preferably one which doesn't use toroids!
Here's the description of the antenna at various bands.
160m
Use 100uH inductance at the top.
A coaxial stub which is open ended RG58 style coax is 48cm long.
Open ended means just dangle a piece of coax at point J2 with braid to one side and centre to the other. The end is left "open" or with a simple variable capacitor for fine tuning. Results have been reasonable for local working but not amazing. Generally I qso 50 miles or so.
80m
Using ZERO inductance and a 139cm stub plus 5 watts I have made plenty of UK/EU qso's with this antenna. Obviously larger antennas are better but expect your signal to be about 2 s-points down from stations using full size antennas and assuming the same power output.
40m
Using 10 watts I have had some QSO's around the UK but I am not keen on this band so my experience is limited. Zero inductance and a 39cm stub is required.
30m
THIS BAND AND QRP IS BRILLIANT! 5 watts rarely fails to get a QSO. I have only operated in the daytime when I have had numerous QSO's around europe with just 5 watts with no hassle. Just use a 30cm stub and zero inductance.
20m
Numerous european and north american qso's made in the direction of radiation of a normal quad loop. Use 15uH of inductance for best results.
17m
Use a 3cm stub and zero inductance.
Numerous north americans, the middle east on 1 watt and Russian ragchews are easy.
Due to the radiation pattern of the antenna in my QTH I am best placed for north American and middle eastern QSO's.
15m
All over north america, the carribean and some south Americans with 10 watts.
1 watt to the Lebanon and recently my first call was answered by the 3B9C expedition using 25 watts of ssb. Countless europeans of 5w cw. North Americans worked by the truckload. Brazil also worked. Use zero inductance and 6cm of coaxial stub.
12m
Plenty of north americans and europeans. Use 9cm of RG58 stub and zero inductance for best results.
10m
Plenty of north American, the caribbean and the middle east as well as Europeans on 29MHz FM and I only used a max of 25 watts. Brazil also worked. Use 15cm of coaxial stub and zero inductance.
Remember the quad loop up on all these freqs is like a horizontal dipole and as such is directional.
HOWEVER we can perform a useful trick here - use 60uH of inductance and you can rotate the radiation in the opposite direction and with vertical polarisation! A rotatable indoor dipole without rotating it! This time you use 60uH of inductance at the top of the loop and approx 20cm of open ended coaxial stub.
I've worked gawd knows amounts of north americans, south americans, central americans, the middle east, europeans and Russia and south african stations with only 10-20 watts ssb.
Remember all of the above has taken place outside the sunspot maxima.
6m
In the summer sporadic E season it is typical to be able to work distance about 1500 miles. With only 5 watts cw/ssb I have had plenty of qso's at this distance with ease in the direction of the loop, which is in the same direction of a normal quad loop. I don't frequent 50Mhz all that often but it's pleasing to work exactly the same typical distances as every one else with this silly antenna!
NOTES
This antenna is like any other antenna - it's just a resonant circuit that radiates. The loop is the inductance and all you need to do is add the required capacitance to it to for a tuned and radiating circuit.
Rules of thumb are that the smaller the loop the more capacitance you need to resonate it. When tuning a coaxial stub you simply snip off 5mm at a time to provide the required match. Circumstances vary! So be prepared for slight differences to stub lengths etc. It is perfectly in order to have a reasonable variation in loop length and adjust sub length/variable capacitance in order to suit.
All polarisation is horizontal except for 160m where it is vertical OR on 28Mhz using 60uH inductance it also becomes vertical polarisation.
This antenna as described is in use by G0FTD every day and provides many happy hours of operating - so I know it works.
With the restrictions placed upon so many of us these days it really is pleasing to report a real antenna that allow just about anyone to play amateur radio with some sense of normality. Youngsters with parents can put up this antenna in their bedrooms, pensioners can (and have) used this antenna in retirement homes and restricted accommodation, students and flat dwellers can use it to at least continue their chosen hobby.
Noise is a big problem on receive and is often very restrictive. Sorry folks but it's a problem we ALL suffer from. Apart from operating at night when hopefully the local TV's have been turned off there's not a lot we can do.
CONCLUSION
Amateur radio IS possible under the most extreme circumstances so long as you don't expect all freqs to be 100% qrm free on recieve and that you'll have to expect your signal to be a few s-points lower. In practice it's not really a problem and then it pays to think that if your using a bit of "damp string" and a few watts your acheivement is damn good compared to all the sillywotsits who spent 1000's of euros/pounds/dollars and massive
effort for towers/kilowatt amps/expensive aluminium tubes to make yagi's blah blah.
It's all relative folks - so enjoy amateur radio under your own circumstances and stop feeling left out!
A BETTER LF ANTENNA.
I have also tried a 4.2m x 2.4m loop with excellent results on the LF bands. It seems to outperform the previous antenna on the LF bands by quite a large margin. The antenna is a corner fed loop as shown here.I have NOT tried coaxial stubs with this antenna. I have only use an atu for matching at the point of J1. Never use an atu at the rig end!
However, I have used computer modelling to assist me attain a high degree of accuracy with the previous antenna, so here are the recommended starting points for using open ended coaxial RG58 stubs.
Band | Stub Length | |
160m | 70cm stub | |
80m | 5cm | |
40m | 19cm | |
30m | 38cm | |
20m | 48cm | |
17m | 6cm | |
15m | 7cm | |
12m | 12cm | |
10m | 5.5cm | |
6m | 8.5cm |
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