On 11/1/2015 11:38 AM, Jeff Liebermann wrote:
I've been thinking of building a rather different magnetic loop
antenna. Instead of the usual rigid loop and adjustable tuning
capacitor, I want to try a flexible loop and a fixed capacitor. The
idea is to eliminate the cost of the tunable vacuum capacitor or
cheese grater butterfly capacitor.

For a loop, I propose to use a flexible aluminum dryer vent hose:
https://www.google.com/search?tbm=isch&q=flexible+dryer+vent+duct
http://www.ipagepro.com/dryerventsolutionsllc/logos/BTD48.png
http://ace.imageg.net/graphics/product_images/pACE3-17458764enh-z8.jpg
I've used similar hoses in my giant inflatable rubber ducky antenna
experiments. The major point of failure was that the spiral steel
wire antenna inside the hose produced some hot spots, which melted a
hole in the vinyl jacket. However, with an aluminum jacket, all the
RF will be on the outside, and there's no vinyl to melt.

The 8ft dryer hose will (somehow) form a loop when inflated with air
from a bicycle or hand pump. Inside the dryer hose is a length of
small diameter bungee cord to help collapse the loop. When hose is
inflated, the loop expands, which also tunes the loop to the desired
frequency.

One nice feature is that with the loop deflated and collapsed, it's
sufficiently small for portable or stealth use. Fully inflated, an
8ft hose should produce a 31" diameter loop.

The rest is fairly conventional. A small wire loop inside the loop to
provide impedance matching and coupling for the 50 ohm feed. Maybe
some kind of tuning indicator (small fluorescent tube). I'm undecided
on whether to mount it vertically, which requires a prop, or
horizontally, which can be done on an insulated table surface.

Permission to steal and use this idea is hereby granted, as long as
you fail to mention my identity in the event that your sanity is
questioned by the neighbors or local authorities. No patents are
pending.




Probable should clear the lint out first!

Paul, KD7HB

On Sun, 1 Nov 2015 18:10:56 -0800, Paul Drahn
wrote:

Probable should clear the lint out first!
Paul, KD7HB

I know that hams are cheap, but I didn't realize that extended to
stealing the neighbors dryer vent hose in order to build an antenna. I
highly recommend purchasing a new hose, which comes pre-cleaned:
http://www.acehardware.com/family/index.jsp?categoryId=2627981

Incidentally, there's no requirement that the entire loop be made from
expandable hose. The loop could be in the form of a square loop,
where the flat base and flat top are rigid aluminum structures, and
the two vertical sections are flexible dryer vent hose. The weight of
the flat top would help collapse the antenna although I suspect that
springs or weights would work better.

It's not like inflatable antennas and structures are a new thing:
http://ltaprojects.com/towers/inflatable-antenna-video-towers/ham

--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

On 11/1/2015 6:42 PM, Jeff Liebermann wrote:
On Sun, 1 Nov 2015 18:10:56 -0800, Paul Drahn
wrote:

Probable should clear the lint out first!
Paul, KD7HB

I know that hams are cheap, but I didn't realize that extended to
stealing the neighbors dryer vent hose in order to build an antenna. I
highly recommend purchasing a new hose, which comes pre-cleaned:
http://www.acehardware.com/family/index.jsp?categoryId=2627981

Incidentally, there's no requirement that the entire loop be made from
expandable hose. The loop could be in the form of a square loop,
where the flat base and flat top are rigid aluminum structures, and
the two vertical sections are flexible dryer vent hose. The weight of
the flat top would help collapse the antenna although I suspect that
springs or weights would work better.

It's not like inflatable antennas and structures are a new thing:
http://ltaprojects.com/towers/inflatable-antenna-video-towers/ham

I am looking at the vent pipe from our reflow oven. We made it up from
4", 4' long vent pipe pieces, including "T" and "EL" pieces. That should
work better than the expandable dryer vent hose.

Paul, KD7HB

On 11/3/2015 11:59 AM, Paul Drahn wrote:
On 11/1/2015 6:42 PM, Jeff Liebermann wrote:
On Sun, 1 Nov 2015 18:10:56 -0800, Paul Drahn
wrote:

Probable should clear the lint out first!
Paul, KD7HB

I know that hams are cheap, but I didn't realize that extended to
stealing the neighbors dryer vent hose in order to build an antenna. I
highly recommend purchasing a new hose, which comes pre-cleaned:
http://www.acehardware.com/family/index.jsp?categoryId=2627981

Incidentally, there's no requirement that the entire loop be made from
expandable hose. The loop could be in the form of a square loop,
where the flat base and flat top are rigid aluminum structures, and
the two vertical sections are flexible dryer vent hose. The weight of
the flat top would help collapse the antenna although I suspect that
springs or weights would work better.

It's not like inflatable antennas and structures are a new thing:
http://ltaprojects.com/towers/inflatable-antenna-video-towers/ham

I am looking at the vent pipe from our reflow oven. We made it up from
4", 4' long vent pipe pieces, including "T" and "EL" pieces. That should
work better than the expandable dryer vent hose.

I think the point is that the flex tubing antenna can be tuned by
adjusting the loop rather than the capacitor. Interesting idea although
it may not prove practical in the end.

--

Rick