Indoor Fan Dipole

[FireArcherIIc]

I am trying to build a multiband antenna for medium and shortwave listening. I will not be transmitting with this antenna. I found a website and tried to follow the design, except for indoors rather than outside. I live in an apartment. As I have limited space, I thought that I could bend the antenna to follow the ceiling wall corners of the room. I would start in the middle of one wall with a common feed point, and run the legs away from there, turning at the corners as needed. I understand it is not a great idea, but will the different legs give me an advantage over just a single band dipole? Attached is a JPG to help visualize the idea. the cyan line going down if the coax feed to the receiver. Thanks for the help.

 

[LtDoc]

Would there be any benefit in an antenna such as you proposes? Yes, there can be. There appear to be 4 antennas there, so you would/could have a resonant antenna on four bands. That tends to be 'better' than just a single antenna used on multiple bands where it isn't resonant.
But naturally, there are 'catches' to that 'better' thingy. I figure you are aware of what at least a couple of those 'catches' are. The first that comes to mind is that the thing is inside rather than outside. That means that there will be some attenuation of a received signal because of what's between that antenna and the source of the signal (walls, etc.). Another 'catch' is that because of the shape of the antenna there will be some variations in it's reception/radiation pattern. It may work just dandy in particular directions and not so good in others. And then there's always polarization, vertical/horizontal, and that will depend on what those 'other' stations are using.
So, would your antenna be worth making? Sure, why not? Best thing since sliced bread? Probably not, but it certainly beats not having an antenna at all.
- 'Doc


(And the 'best' part... it's a cheap alternative to buying an antenna!)

 

[thomast77]

It will also affect impedance. But that is not an issue with receive only antennas. I have a similar setup. Just a random wire run around the inside of my bedroom. It's somewhere around 45 ft. I have it connected to a kaito 1103. I wasn't happy with reception. So I got an idea you might want to consider. The kaito uses an 1/8" phone jack for the antenna. I connected the random wire to the center pin. Then I connected a short wire (as short as possible) to the shield of the phone plug, and run that to a ground rod right out side the bedroom window. In my case about 5' long. It opened the reception right up and made a huge difference for shortwave.

 

[prcguy]

Impedance mismatch will have the same effect on transmit and receive. Try using a dipole with half wave elements (full wavelength overall) fed with 50 ohm coax and see how bad it is due to the very high impedance feedpoint being loaded down by the low impedance transmission line.

Or take a 3ft whip which has an extremely high impedance at lower HF and stick it on the end of a long piece of 50 ohm coax and you'll not hear much, but place a 9:1 or higher ratio impedance matching transformer between the whip and coax and it will come alive with signals.

prcguy

It will also affect impedance. But that is not an issue with receive only antennas. I have a similar setup. Just a random wire run around the inside of my bedroom. It's somewhere around 45 ft. I have it connected to a kaito 1103. I wasn't happy with reception. So I got an idea you might want to consider. The kaito uses an 1/8" phone jack for the antenna. I connected the random wire to the center pin. Then I connected a short wire (as short as possible) to the shield of the phone plug, and run that to a ground rod right out side the bedroom window. In my case about 5' long. It opened the reception right up and made a huge difference for shortwave.

 

[FireArcherIIc]

OK. So should I use a balun on this antenna, or should I try to find some ladder line as the feed to the receiver. Sorry, I don't know antenna theory very well, so I have to look up impedance. I do appreciate the help very much.