TheRadioBoard

Forum for the homemade radio builder. Newbies and Experts and everyone else are welcome here!
It is currently Sat Oct 25, 2014 9:07 pm

All times are UTC




Post new topic Reply to topic  [ 20 posts ]  Go to page 1, 2  Next
Author Message
 Post subject: AM/SW Crystal Set
PostPosted: Sun Aug 30, 2009 11:14 pm 
Dear Fellow members-Although a newbie to xtal sets, I built an xtal AM radio with a separate antenna coil, a Steinite Wavetrap , a simple Tuggle, multiple taps on the antenna coil, Piezo headphones and an amplified speaker for cheating on the weaker signals. In my defense, I live in a third floor stucco apartment, and even many of my restored superhet receivers have difficulty receiving clearly many stations.
I have incoming a nicely wound Litz coil with an AM and 2 SW coils on the form. ANY info, links, advice or leads building crystal SW sets is greatly appreciated:)-Gearhead


Top
  
 
 Post subject: Re: AM/SW Crystal Set
PostPosted: Sun Aug 30, 2009 11:50 pm 
Offline
User avatar

Joined: Tue May 01, 2007 12:18 am
Posts: 2231
Location: Vieques, PR
gearhead222 wrote:
Dear Fellow members-Although a newbie to xtal sets, I built an xtal AM radio with a separate antenna coil, a Steinite Wavetrap , a simple Tuggle, multiple taps on the antenna coil, Piezo headphones and an amplified speaker for cheating on the weaker signals. In my defense, I live in a third floor stucco apartment, and even many of my restored superhet receivers have difficulty receiving clearly many stations.
I have incoming a nicely wound Litz coil with an AM and 2 SW coils on the form. ANY info, links, advice or leads building crystal SW sets is greatly appreciated:)-Gearhead


It would be interesting to see this coil. Litz really isn't a good choice for SW coils. Can't say that it hurts but plain solid wire of the same physical size will perform better than litz above a few MHz.

Then there's the Tuggle. No experience here using a Tuggle at SW and I guess I'm looping back (bad pun) to how its used with this particular coil.

A good antenna is your best friend. Maybe you can throw a wire out of the window - even if its temporary at listening times?

Ya got a schematic drawn up of how you're going to configure this?


-Bill


Top
 Profile  
 
 Post subject:
PostPosted: Mon Aug 31, 2009 12:54 am 
Offline

Joined: Tue Jan 15, 2008 4:26 pm
Posts: 1075
Location: Dallas, Tx.
There are no local high power stations. The closest that he falls within the borderline antenna patterns are in San Antonio and his apartment and another stucco one block the signal path. I could find no target stations from his balcony. I think he would have better results in the SW band.
The Tuggle can be used to improve his BCB sets and a similar type tuner I use occasionally will work well on the lower portions of the SW band with a modified SW Mystery set.


Top
 Profile  
 
 Post subject:
PostPosted: Mon Aug 31, 2009 6:24 pm 
Dear Fellow Members-Homebrew has really helped me out with my first xtal set, although I really appreciate all of your replies.
I have a Bogen xformer, a set of Chinese EH-5 S/P headphones, a 0-430 pF variable cap from MRL and have incoming Litz wire Wavetrap/Tuggle coils along with caps for each of these coils. I also have another Litz wire detector coil coming from the same supplier, along with a huge variety of germanium diodes and transistors to use.
The S/W xtal set is an afterthought, as the same coil supplier threw it in with my other parts. Perhaps a 1 tube regen SW receiver would be a better idea.
As HB mentioned, most of my superhet AA4, AA5 and AA6 don't receive that many stations. The only decent tube performers I have are my Hammarlund HQ-100A, my 1953 Silvertone 2016, my Zenith G500 Universal AM portable and my tube Zenith Transoceanics.
Will keep you all updated on the second xtal set, as I am still receiving parts for it-Gearhead.


Top
  
 
 Post subject:
PostPosted: Tue Sep 01, 2009 10:56 pm 
Offline

Joined: Tue Jan 15, 2008 4:26 pm
Posts: 1075
Location: Dallas, Tx.
"It would be interesting to see this coil. Litz really isn't a good choice for SW coils. Can't say that it hurts but plain solid wire of the same physical size will perform better than litz above a few MHz. "
*
When designing a Litz cylinder coil I can look past the BCB and adjust the wire spacing for minimal amplitude on large SW signals eliminating the need for a choke. I would think you could maximize the SW band doing the same thing on a SW frequency size coil.
I've found popular opinion on Litz to be false in a couple other situations. Antennas and tapped coils work exceptionally well compared to their solid wire counter parts.
Bottom line to me is that the Litz offers a lot less RF resistance than the equivalent solid wire, making a better coil or antenna.
I've been slowly pulling my best xtal designs and copying the coils in Litz. I have my SW Mystery set pulled to try in Litz soon.


Top
 Profile  
 
 Post subject: Re: AM/SW Crystal Set
PostPosted: Tue Sep 01, 2009 11:30 pm 
exray wrote:
Litz really isn't a good choice for SW coils. Can't say that it hurts but plain solid wire of the same physical size will perform better than litz above a few MHz.


This kind of blows me away.

I thought the reason for using litz was because the current flow of AC (as compared to DC) moves from the whole wire toward the outside (surface) of the conductor, and since lizt is many small strands of wire braided together it has a greater "surface area" than a single solid wire of the same size and it offers less resistance to AC signals.

And unless I'm mistaken, as the AC frequency goes up the "skin effect" also increases. Seems to me that as the frequency increases the advantage of litz wire would also increase.... Am I wrong or am I missing something here?


Top
  
 
 Post subject:
PostPosted: Tue Sep 01, 2009 11:44 pm 
Offline

Joined: Sat Aug 18, 2007 8:52 pm
Posts: 2726
Location: Australia
Logically(?) if the frequency gets too high, then the signal will avoid entering the interior of the litz bundle at all and prefer to "crawl" across the external surface of the bundle - transferring power by "radiation" rather than conduction? in which case, solid wire or tube would be better, in that transfer is aided by some conduction as well, rather than having to radiate (leap) from strand to strand on the surface of the litz?

My uninformed take.


Last edited by golfguru on Wed Sep 02, 2009 12:50 am, edited 2 times in total.

Top
 Profile  
 
 Post subject: Re: AM/SW Crystal Set
PostPosted: Wed Sep 02, 2009 12:40 am 
Offline
Site Admin
User avatar

Joined: Sat Jun 06, 2009 6:58 pm
Posts: 3281
Location: South Florida
Microbes wrote:
I thought the reason for using litz was because the current flow of AC (as compared to DC) moves from the whole wire toward the outside (surface) of the conductor, and since lizt is many small strands of wire braided together it has a greater "surface area" than a single solid wire of the same size and it offers less resistance to AC signals.

Litz wire mitigates skin effect up to about 1 MHz. I believe that as you go higher in frequency the coupling between the wires reduces the advantage of using Litz wire. Something called "proximity effect," where the field in one wire affects the fields in other nearby wires.

73,

_________________
Image
http://kr1s.kearman.com/
http://qrp.kearman.com/


Top
 Profile  
 
 Post subject:
PostPosted: Wed Sep 02, 2009 2:58 am 
Offline
User avatar

Joined: Tue May 01, 2007 12:18 am
Posts: 2231
Location: Vieques, PR
Two additional parameters.

The wire gauge is also a player in the equation. Theoretically you need to be well into to 50+ gauge range on SW to replicate what we see on MW. MW tends to peak out with 46 gauge...maybe 48-ish on the high end of the band. Thats well proven.

Then there's the twist of the wires. Part of the magic with litz is the number of twists-per-foot which is crucial to keep the RF 'spread out' among the individual conductors to take advantage of the skin effect improvement.

Every evaluation of BCB quality litz (44-46-48 gauge) that I have ever seen shows a substantial drop off after a couple of MHz. I've never actually seen or heard of 50+gauge litz so I can't guess if it could/would display the same characteristics.

Besides...solid wire is much less expensive at that point!


Top
 Profile  
 
 Post subject:
PostPosted: Wed Sep 02, 2009 4:16 am 
Quote:
Logically(?) if the frequency gets too high, then the signal will avoid entering the interior of the litz bundle at all and prefer to "crawl" across the external surface of the bundle - transferring power by "radiation" rather than conduction? in which case, solid wire or tube would be better, in that transfer is aided by some conduction as well, rather than having to radiate (leap) from strand to strand on the surface of the litz?


I knew that the reason HF and VHF transmitter coils are sometimes made of 1/4 or 3/8 or even 1/2 inch copper tube instead of soild wire was that there is much more "surface area" per lb. of copper using tubing instead of solid wire (and solid copper wire 3/8" diameter would cost a fortune and be really hard to work with).

But with transmitters you are dealing with alot of power compared to what flows in a X-tal set's coil and I always figured that litz wire large enough to handle those kinds of currents would be prohibitively expensive so they used tubing instead.

Quote:
Litz wire mitigates skin effect up to about 1 MHz. I believe that as you go higher in frequency the coupling between the wires reduces the advantage of using Litz wire. Something called "proximity effect," where the field in one wire affects the fields in other nearby wires.


Sounds almost like "self capacitance" in a close wound coil. Or maybe it sets up eddy currents that interfer with resonance of the coil and kill the Q?

Quote:
Every evaluation of BCB quality litz (44-46-48 gauge) that I have ever seen shows a substantial drop off after a couple of MHz. I've never actually seen or heard of 50+gauge litz so I can't guess if it could/would display the same characteristics.


Well... I quess I learned something today. :)

Quote:
Besides...solid wire is much less expensive at that point!


I think solid wire is less expensive than litz at all points. :lol:


Top
  
 
 Post subject:
PostPosted: Wed Sep 02, 2009 6:06 am 
Offline

Joined: Sat Aug 18, 2007 8:52 pm
Posts: 2726
Location: Australia
This paper tells you a lot more about litz than you ever wanted to know.
http://engineering.dartmouth.edu/induct ... litzcj.pdf


Top
 Profile  
 
 Post subject:
PostPosted: Wed Sep 02, 2009 10:37 am 
Offline

Joined: Tue Jan 15, 2008 4:26 pm
Posts: 1075
Location: Dallas, Tx.
I hate to see transmitting and industrial maxims applied to xtal technology.
Proximity effect is the losses associated with outside fields as in electric motors and adjacent wiring in bundles. It is the losses associated with unequal currents. In litz adjacent currents should be equal and wire spacing eliminates the adjacent wire proxmity effect for the most part.
A major contributor in the loss formulas is Iac squared. The crystal set current is too low to have a major effect.
A example of Iac not necessarily xtal set range is 3ma squared = .000009.
Increase that to 9 ma and you have .000081.
Not a linear progression.
In electric motors and transmitters it is a major factor.
In xtal sets it is way too low to even consider.
I can not get the two numbers to line up for the revision in the text.
.000009
.000081


Last edited by homebrew on Thu Sep 03, 2009 4:41 am, edited 1 time in total.

Top
 Profile  
 
 Post subject:
PostPosted: Wed Sep 02, 2009 4:49 pm 
Dear Fellow Members and Homebrew-As HB already knows, I have decided to start work on a simpler Dave Schmarder xtal SW design. Here's the link:

http://schmarder.com/radios/crystal/09.htm

I found a 3-60pF variable cap that Dave told me would increase the tuning range. It was also recommended that I loosely couple the antenna and tank coils. Any suggestions for changing the stock tank/antenna coil windings is greatly appreciated.
I will be installing my Bogen xformer on a separate board and try the Trimm 2000 ohm, Scmarder Piezo headphones and also my Chinese EH--5 military soundpowered headphones, once I get the set built. Still unsure what to use for coil forms, especially if I make a loosely coupled set-Gearhead


Top
  
 
 Post subject:
PostPosted: Wed Sep 02, 2009 7:25 pm 
Offline
Site Admin
User avatar

Joined: Sat Jun 06, 2009 6:58 pm
Posts: 3281
Location: South Florida
homebrew wrote:
A example of Iac not necessarily xtal set range is 3ma squared = 9.
Increase that to 9 ma and you have 81. Not a linear progression.
In electric motors and transmitters it is a major factor.
In xtal sets it is way too low to even consider.


Three mA (0.003 A) squared is 9 uA (0.000009 A).

73,

_________________
Image
http://kr1s.kearman.com/
http://qrp.kearman.com/


Top
 Profile  
 
 Post subject: Math error
PostPosted: Thu Sep 03, 2009 1:28 am 
Offline

Joined: Sun Dec 02, 2007 7:50 am
Posts: 1377
HaHa good one. lol

1/2 a dollar squared is 1/4 of a dollar but 50 cents squared IS 2500 cents and that is 2.5 dollars!

Be carefull when multiplying or squaring "fractional" numbers.


Top
 Profile  
 
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 20 posts ]  Go to page 1, 2  Next

All times are UTC


Who is online

Users browsing this forum: No registered users and 0 guests


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot post attachments in this forum

Search for:
Jump to:  
Powered by phpBB® Forum Software © phpBB Group
Americanized by Maël Soucaze.