RadioBanter - View Single Post - Fuel Tanks and Cereal Silos as Cavity Resonators for HF

September 23rd 03, 06:25 PM

In article ,
(SpamLover) wrote:

Just out of curiosity - Did anyone ever try a cabinet-sized or
room-sized cavity resonator as roof filter in a HF receiving system?

I've trawled a bit for construction details, and found that a squat
cylindrical resonator may have a radius of a quarter wave, so say...

IF, MHz Diameter, feet what on earth?
-----------------------------------------------------
100 .49 a big can?
45 11 a fuel tank?
9 55 ????

It would be cool to use a whole room as a resonator, adding furniture
or guests as a way of trimming frequency or Q factor.

For mobile use, one might consider using a whole truck trailer as a
resonator.

I would not mind dumping a truck trailer behind the sheds at my
parents' farm and running some coax there and back, for a bit of HF
work during my weekend visits. Besides, they also have a couple of
unused silos, with cavities 15 ft in diameter and about 40 ft height.
I wonder if such cavities in series would be tight enough to provide
enough selectivity for CW work. They also have a huge pistoning lid
hanging inside from a crane, which could be used for tuning. So
perhaps they could provide ALL the filtering right at the fundamental
frequency, like: rhombic antenna - coupler - silo 1 - coupler -
silo 2 - coupler - product detector - audio chain. Too bad they're
reinforced concrete and would need lining. A neighbour & friend has
new, shiny, airtight aluminum ones. His son is an electrical
engineer. Hmmmm.

Please do laugh, but comment constructively! I am an ignorant
coil-winder. Where do I read up on resonators and coupling? I would
not mind experimenting with a stack of barrel-sized filters if the
numbers warrant it.

I'm not laughing! In the 60's, we had a problem with a shielded room.
The electrical noise within it was horrendous. It turned out that the
room size happened to be just right to resonate with the radiation from
the gigantic 5 MW SAGE radar which was just hundreds of feet away. the
solution was to move the sensitive gear out of that room and to another.
There was no way we could modify the radar nor the room; esp. the radar
which had a football field sized rotating antenna.

Al

--
There's never enough time to do it right the first time.......