08-03-2017, 11:44 AM
Mention of 75 ohm twin feeder reminds me of the quick'n'dirty method of making an indoor FM aerial:
- Choose a wall that is as close to broadside onto the transmitter as possible;
- Take a suitable length of flat two-core mains lead and strip the outer sheath back 2' 7";
- Separate the two conductors and stretch them out along the picture rail, securing them with drawing pins at intervals as required;
- Connect the other end of the flex to a plug to suit the input of the FM radio.
I've no idea how close twin flex is to 75 ohm feeder but it worked well, anyway!
Although the 2' 7" measurement has been fixed in my mind for over 50 years, I'd never bothered about checking it but, allowing for the elements being only 95% of the wavelength in free air, I calculate it to be 91MHz which would have been the centre of the small portion of Band II that HMG grudgingly allowed the BBC to use in those days!
Two other figures rattling around at the back of my mind are 10' 10" for the length of a half-wave dipole for channel B1 and 2' 3½" for channel B9.
Funny thing, the mind. It can pluck figures like that out of the dim, distant past yet if Helen asks me "How much did you have to drink last night?" I can never remember the answer ...![[Image: drink.gif]](http://i260.photobucket.com/albums/ii16/ktype_photo/sm/drink.gif)
- Choose a wall that is as close to broadside onto the transmitter as possible;
- Take a suitable length of flat two-core mains lead and strip the outer sheath back 2' 7";
- Separate the two conductors and stretch them out along the picture rail, securing them with drawing pins at intervals as required;
- Connect the other end of the flex to a plug to suit the input of the FM radio.
I've no idea how close twin flex is to 75 ohm feeder but it worked well, anyway!
Although the 2' 7" measurement has been fixed in my mind for over 50 years, I'd never bothered about checking it but, allowing for the elements being only 95% of the wavelength in free air, I calculate it to be 91MHz which would have been the centre of the small portion of Band II that HMG grudgingly allowed the BBC to use in those days!
Two other figures rattling around at the back of my mind are 10' 10" for the length of a half-wave dipole for channel B1 and 2' 3½" for channel B9.
Funny thing, the mind. It can pluck figures like that out of the dim, distant past yet if Helen asks me "How much did you have to drink last night?" I can never remember the answer ...
