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SW DXing with a crystal radio?



 
 
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  #1  
Old October 21st 04, 12:26 AM
Richard
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Default SW DXing with a crystal radio?

Has anyone tried it. Came across a few links on the topic, seems fun.

73's
Richard, Warsaw


  #2  
Old October 21st 04, 02:54 AM
Dave
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"Richard" wrote in message
...
Has anyone tried it. Came across a few links on the topic, seems fun.


It IS fun. But you need patience, and a good antenna. And
don't even THINK of selectivity. I ran mine through an audio
amp, and an Autek audio filter, but still broad as a barn. But
for a radio with 5 parts, you can't expect a Kenwood R5000!


  #3  
Old October 21st 04, 06:46 AM
GrtPmpkin32
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I've built a number of crystal radios over the last few years, and really enjoy
the entire process, from winding coils to stringing up long wires and grounding
everything. I have DX'ed some decent hauls, though a set like that is not going
to be as selective as a more robust rig. I've made tuners and added stages in
some of my crystal sets to add some selectivity, and while this does tend to
reduce the level of the signal (to the point where real long-haul DXing is no
longer a reasonably reliable goal), when conditions permit nice DX, adding
extra stages of tuning and selectivity help a LOT. But you really need to like
tinkering, and fiddling with everything, to get the strongest, cleanest
reception. And have a very good ground!
But I find it's worth every bit of it!
Good luck-
Linus

Richard wrote:
Has anyone tried it. Came across a few links on the topic, seems fun.



  #4  
Old October 21st 04, 03:48 PM
Bill
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Default

I sure would appreciate some of your plans for making a shortwave crystal
set. Some coil dimensions, wire size and such. thanks.


  #5  
Old October 21st 04, 07:27 PM
GrtPmpkin32
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I sure would appreciate some of your plans for making a shortwave crystal
set. Some coil dimensions, wire size and such. thanks.


Go he

www.midnightscience.com

It's the homepage of the Xtal Set Society, and they have numerous plans and
projects available, as well as books, kits and components (wire, variable
capacitors, etc.)
for making xtal sets. They also have a lot of great links for xtal set builders
and enthusiasts. An invaluable resource, and much more inclusive and helpful
for the beginner and the expert than I could possibly give you in this
newsgroup.
Have fun!
Linus
  #6  
Old October 22nd 04, 05:18 PM
bpnjensen
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Default

(GrtPmpkin32) wrote in message ...
I sure would appreciate some of your plans for making a shortwave crystal
set. Some coil dimensions, wire size and such. thanks.


Go he

www.midnightscience.com

It's the homepage of the Xtal Set Society, and they have numerous plans and
projects available, as well as books, kits and components (wire, variable
capacitors, etc.)
for making xtal sets. They also have a lot of great links for xtal set builders
and enthusiasts. An invaluable resource, and much more inclusive and helpful
for the beginner and the expert than I could possibly give you in this
newsgroup.
Have fun!
Linus


Hey, Linus, I do have a couple of questions for which you may know
answers -

(1) On crystal sets, is it better to use small-gauge enameled wire, or
larger gauge insulated wire for greater wrap spacing? On my sets, I
have used insulated large wire for spacing and ease of handling, and
they seme to work pretty well, but I wonder if the greater number of
wraps or closer spacing of the smaller wire would gain anything...?

(2) On the inductive secondary coil, which avoids a direct connection
to the antenna and also increases selectivity, is it better to have
that coil the same diameter as the main coil and make it fixed OR
moveable wrt to the main coil, or is it better for that secondary coil
to be smaller so it can slide within the larger main coil? I have
used the latter method with some success, but have not tried the
first.

Thanks, and wishing you much fun!
Bruce Jensen
  #7  
Old October 22nd 04, 07:05 PM
GrtPmpkin32
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Default

(1) On crystal sets, is it better to use small-gauge enameled wire, or
larger gauge insulated wire for greater wrap spacing?


I don't think it's that crucial as a rule, though it would depend on a number
of variables (dimensions of coil form/s, freq. range desired, and so on). I
have generally tended to use enameled wire, anywhere from 26g. to 14g., simply
because that's what I had on hand. The larger wire you use may be working for
more gain in your set than in one with the same size coil but with smaller
wire, all things being equal (though they rarely are)... so it's a matter of
tinkering and trying it out. I find it easier to use smaller enameled wire for
winding and so on. Litz wire would be the best, though it's more difficult (and
expensive) to come by.

I wonder if the greater number of
wraps or closer spacing of the smaller wire would gain anything...?


Again, it depends on the intended freq. range and desired use of the
builder/user. Additional windings on a coil will effectively lower the freq.
range of the coil (i.e., if your current coil doesn't reach down into the 500
or 600 kHz portion of the MW band, adding windings on your coil will get you
there), and having them more or less closely spaced will affect those aspects
as well. You would benefit from such changes only if you desired what those
changes would give you, but if you're happy with what you currently have, then
it wouldn't 'gain' you anything...

(2) On the inductive secondary coil, which avoids a direct connection
to the antenna and also increases selectivity, is it better to have
that coil the same diameter as the main coil and make it fixed


Again, it really depends on what you want as an end result. A more loosely
coupled inductor will have different properties than a tightly-fixed set up,
and while this may be more flexible for some users, others may wish to keep
things simpler. I have almost always used a fixed secondary formed over the
primary, though I've played with movable pick-up coils as well. For SW work,
the movable type seemed to help with selectivity more than a fixed type, and
the addition of an antenna trap/tuner in the circuit helped even more.

OR
moveable wrt to the main coil, or is it better for that secondary coil
to be smaller so it can slide within the larger main coil? I have
used the latter method with some success, but have not tried the
first.

I don't believe I've ever attempted having the secondary coil inside the
primary coil form, so I can't really comment with any credibility (not that
this fact stopped me from commenting on the rest of this post, hahah!). I have
used a number of different set ups with respect to inductor size, windings,
secondary or 'pick-up' coil size and windings, and found that each had their
own advantages and disadvantages, and depending on what I wanted that day, I
chose accordingly.
I guess the upshot of this entire rambling post from an intermediate-knowledge
xtal set builder, is that every element of the set affects all other elements
in a fundamental way, and each and every variation or combination of those
variables results in essentially a different receiver. What is "better" to some
may be useless to others (much like antennas in general) so it's sort of a moot
point, EXCEPT that simply going for it and experimenting with all the
variations is so much fun that you'll know when you've come up with something
that really IS better for you, and keep improving from there. I may need to
build a set with an inner secondary, since I had not ever really thought about
that variation before... might result in crap, might result in some surprising
reception.
Geez, I hope this has been of some help.
And hopefully there are others in here who have a better knowledge of your
questions, and they can provide more insight.

Linus
  #8  
Old October 23rd 04, 04:50 AM
starman
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Posts: n/a
Default

bpnjensen wrote:

Hey, Linus, I do have a couple of questions for which you may know
answers -

(1) On crystal sets, is it better to use small-gauge enameled wire, or
larger gauge insulated wire for greater wrap spacing? On my sets, I
have used insulated large wire for spacing and ease of handling, and
they seme to work pretty well, but I wonder if the greater number of
wraps or closer spacing of the smaller wire would gain anything...?

(2) On the inductive secondary coil, which avoids a direct connection
to the antenna and also increases selectivity, is it better to have
that coil the same diameter as the main coil and make it fixed OR
moveable wrt to the main coil, or is it better for that secondary coil
to be smaller so it can slide within the larger main coil? I have
used the latter method with some success, but have not tried the
first.

Thanks, and wishing you much fun!
Bruce Jensen


Regarding the wire size and coil dimensions, do a web search on the
topic of 'Q' or 'quality factor' as it applies to making an RF inductor
(coil). The 'Q' of a coil will determine how selective it is. This will
determine how well you can tune a particular station without hearing
other interfering stations on different frequencies.


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