T
Tauno Voipio
Guest
On 26.3.17 17:35, Joerg wrote:
Joerg, you seem not understand the innermost sense of the crystal-
radio people. They are closely related to audiophools, and it is
quite impossible to use sensible technical argumentation here.
The question of best MF band coils has been solved already in the
1930's: A honeycomb coil wound with Litz wire (gloves on). The
canonical fixing / insulating material is beeswax.
--
-TV
On 2017-03-25 18:39, rickman wrote:
On 3/25/2017 3:30 PM, Joerg wrote:
On 2017-03-25 10:49, rickman wrote:
On 3/24/2017 4:36 PM, Joerg wrote:
On 2017-03-24 10:59, rickman wrote:
On 3/24/2017 1:14 PM, Joerg wrote:
On 2017-03-20 02:06, Tauno Voipio wrote:
[...]
Please do not use PVC as RF insulation or support pieces.
It is lossy to extremely lossy at RF.
Plasticized PVC ain't stellar but not horrid.
http://g3ynh.info/zdocs/comps/part_6.html
Or do they add a lot of vispipuuro into the mix in Finland?
Are you reading the same page? It says PVC Tanδ is 0.04 - 0.14 at 1
MHz. That is in no way acceptable for the sort of high Q circuits
that
are being discussed. That's comparable to wood, 0.059.
This page even lists PVC in the "Lossy" group as defined by Tanδ âĽ
0.01.
The losses in ferrite rods are nothing to sneeze at in comparison. I
have used both in ham radio a lot when I was young. I built kilowatt
level RF power amps, impedance matching boxes and similar gear.
Ferrite
rods in transmitters sometimes became so hot that you could barely
touch
them while inductors wound on some random piece of PVC pipe remained
cool. I don't remember the PVC type other than that it was remnants
they
sold for pennies in the plumbing department so that was very likely
well
plasticized.
Maybe I don't recall the context of the ferrite, but the receiving
antennas in much of this thread and described in detail at Kleijer's
web
site showed measurable losses with better plastics than PVC. Even
cardboard was a poor support relatively speaking. Seems he would use a
foam type plastic to get some rigidity with a minimum of loss. Foam
PVC
was not bad, but his Q measurements increased significantly with foam
polypropylene. Obviously foam is better because there is less actual
material. Solid PVC would show more pronounced losses.
He does some amazingly detailed work. You might find it interesting.
The LC experiments were reported in a series of web pages. Page 10
doesn't have a link to page 11, but otherwise they are all chained.
Looks like there isn't a page 11.
That's what I was saying. There *is* a page 11, page 10 just doesn't
have a link to it. Go back to the index.
Indeed. I change the number in the URL by hand by starting with page 11
he change the URL structure. Well, I am not complaining, my web site
design skills aren't that great either.
http://www.crystal-radio.eu/enlctest.htm
He gets good Q with PVC. Worse with cardboard but who knows what kind of
stuff he used. It looks like carton material. That is often
post-consumer recycled and you never know what's in it. Water content is
another factor, got to bake it out and then lacquer it immediately
afterwards.
He gets good Q with FOAM PVC. Totally different from solid PVC, much
less of it and a lot more air. The point is foam anything else worked
even better.
Look at page 7. Very nice Q values except for the dirty pipe yet this is
all on regular PVC pipe.
The huge jump in Q in part 3 shows that he used the wrong measurement
setup until then. You can't do this sort of stuff with a 100:1 scope
probe, it has to be at least a high-end FET probe. However, hat off, he
achieved amazing Q values in his experiments.
Look at the Q values he gets in part 7. Those are all regular plumbing
PVC pipes. L16 has lower Q but that PVC tube isn't even particularly
clean. It is important to keep or make them pristine when building
high-Q stuff.
I found it very illuminating his tests with the variable capacitors.
Even parts like bushings were found to make a difference.
I remember that from my ham radio days. Dirty or oxidized rotor contacts
.... phssssst ... PHUT ... *BANG* and worst case that could take the
tubes into the abyss along with it. I also spent part of a Wenol
polishing paste tube keeping the final Pi-filter inductor shiny so it
wouldn't heat up too badly and unsolder a connection to it (which could
also result in a loud bang).
BTW, while such high Q isn't all that useful in practice if you ever
needed that there are simpler means to achieve it. An old method is the
"Q-multiplier". In essence the resonance circuit sits inside an
amplifier stage that is deliberately pulled very close to oscillation.
That shrinks the bandwidth big time.
How do you accomplish that without an amplifier? You did notice the
site is all about *crystal* radios, right?
You need an amplifier for that. If you want to you can make an
energy-harvesting one, sans battery. I mentioned this method purely as a
hint, in case anyone ever needs high Q without making fancy large coils
and babying them.
Joerg, you seem not understand the innermost sense of the crystal-
radio people. They are closely related to audiophools, and it is
quite impossible to use sensible technical argumentation here.
The question of best MF band coils has been solved already in the
1930's: A honeycomb coil wound with Litz wire (gloves on). The
canonical fixing / insulating material is beeswax.
--
-TV