On 11/4/2015 12:41 AM, Jeff Liebermann wrote:
On Tue, 3 Nov 2015 03:37:36 -0500, rickman wrote:

Sorry, but I need to bail out of this interesting discussion for about
a week. I just landed another satellite dish repair job and need to
steal some time.

Yeah, me too.


You have to do that exactly once. After that there is no reason to
leave the joints unsoldered.

I'm not suggesting that one build a loop that is NOT soldered.
However, I am suggesting that TESTING a loop that is not soldered is a
good idea in order to nail the tuning range.

Why silver plate when you can get a bigger improvement by going up in
tube diameter?

Because eventually, one runs out of diameter and has to use other
tricks in order to improve efficiency.

It is not very useful to get a 2.5% improvement. That's the bottom line.


So? If people can't follow instructions they get what they get.

I'm one of those people. I find it embarassing to be caught reading
the instructions. Customers will think I don't know what I'm doing if
they see me reading the instructions. Besides, if the product were
designed correctly, it wouldn't need any instructions.

What about other effects. What happens to the inductance if the loop is
a bit out of plane? Any idea if your loop flexes around in wind or
whatever?

If I can find some mythical spare time, I'll buy an 8ft vent hose,
attach it to my LRC meter, and see what thrashing it around does to
the inductance. That should be a fair indication of what the tuning
might do. For fun, I might just tie it in a knot. Remind me in case
I get distracted by paying work.

As to the minimum size of the antenna.

My interest in the minimum size was inspired by an article that I
can't seem to find right now. The author claimed that scaling a loop
increasing the gain and efficiency, but the SNR (ratio between the
baseline atmospheric noise level picked up by the loop, and the
receive signal level) remains constant until the loop becomes so small
that the noise level drops below the thermal noise floor. I agree
with this but want to test it for myself. That means building a
collection of receive only loops with different L/C ratios. Hopefully,
I can derive or deduce some method for calculating the minimum usable
loop size.

You are now analyzing receiving antennas. That's a gear shift. I've
been discussing transmitting antennas. Big distinction.


.. the formula that surprised me
and made me realize there is a nearly brick wall is for radiation
resistance. It's proportional to the 4th power of the ratio of loop
radius to wavelength... the *4th* power! That is hard to overcome by
any small effect or even moderately large ones. Push just a little bit
and you see huge results, like making your loop 33% larger increasing
the radiation resistance by 3x! (or making your loop 25% smaller
reducing the radiation resistance 3x Makes it hard to get anything
like acceptable efficiency if the loop is even a little too small.

Hmmm... if that's correct, it might be useful for my quest for the
worlds smallest practical HF loop.

Xmit and receive put very different requirements on the antenna. Which
do you wish to optimize? What power level/range are you shooting for?


You posted it to S.E.D. I looked it over but there were runtime
errors that I didn't want to fix. The title is Antenna_trans_loop.asc
dated 2013-02-27.

Are you saying the version I posted didn't even run? Odd. It is late
now, but I'll try to dig it out tomorrow.

It ran, but with errors. I don't have your email address so I'll just
dump it on my web pile probably tomorrow evening.

I seem to recall some errors were reported, but I don't recall them
being of any consequence.


That's why I want to silver plate it. The plating looks to be easy.
Others have talked about being able to solder aluminum by using
something to block the air, but I don't recall the details. It sounds
much more difficult.

Alumiweld. It's actually quite easy if you have an acetylene torch or
MAPP gass burner. Propane works, but I found more is more better. You
buy coated aluminum rod and braze normally. It wasn't difficult but I
did manage to screw up a few joints before I got the hang of it.
http://www.alumiweld.com
https://www.forneyind.com/store/detail/682/oxy-acetylene_welding_brazing_rod/5018/easy-flo_aluminum_brazing_rod_18_x_18_-_12_lbs/
http://www.harborfreight.com/8-piece-low-temperature-aluminum-welding-rods-44810.html
https://www.youtube.com/watch?v=CJ42scaWFnw
https://www.youtube.com/watch?v=y-iw3BiR4IQ
Lots of other videos on aluminum brazing on YouTube.
I have no idea how it will work on thinwall sections.

That's a big deal. It needs to work with thin tubing.

I'm happy with the idea of soldering.


This is cute:
https://www.youtube.com/watch?v=TaSORWC-BMU
They're brazing an aluminum engine block by pre-heating the block in a
Weber barbeque.



--

Rick