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|neazoi||Posted - 11 November 2012 15:1 |
Hello, I am trying to create a crystal set that can be configured on different topologies without the need to change it's components
With just one set one can try many different topologies.
Here is a draft of what I have come on:
I would like your comments on this please
|Richard||Posted - 11 November 2012 21:4 |
My computer gave a warning not to go to this site.
|gzimmer||Posted - 11 November 2012 23:9 |
> My computer gave a warning not to go to this site.
No problems here.
I think your virus program has flagged the main site as potentially dangerous.
|Richard||Posted - 12 November 2012 10:47 |
"I think your virus program has flagged the main site as potentially dangerous."
Correct. I saw the gif image and was about to comment when the flag appeared. Not everyone has virus protection, hence my post. After the fact I performed a full scan which was clean.
One can't be too careful these days. ;)
|neazoi||Posted - 12 November 2012 13:49 |
Hello, I have uploaded this gif file to my website, how else should I attach it, there is not an attach option in the forum.
I am a licensed radio amateur, I wouldn't infect visitors!
Now, back to the topic, I would really like your suggestions on the set I have posted.
|neazoi||Posted - 12 November 2012 13:49 |
Edited by - _J_ on 11/13/2012 1:05:46 AM
|neazoi||Posted - 12 November 2012 13:50 |
Edited by - _J_ on 11/13/2012 1:06:17 AM
|neazoi||Posted - 12 November 2012 13:50 |
Sorry, best we can do.
Edited by - _J_ on 11/13/2012 1:06:43 AM
|neazoi||Posted - 12 November 2012 13:52 |
I thought there was an error with the post, so I did it 3 times, please erase it if you can
|Garry Nichols||Posted - 12 November 2012 19:11 |
If you get an error message after posting, the next thing to do is go back to the main site and come in again to where you posted. There are some issues with the server. That is the work-around.
Your proposed circuit has an awful lot of possible combinations. It is hard to comment on it because it could be wired up in many different ways. Do you think that you need so many traps?
One thing that stands out to me is that you seem to be attempting to tune the two stages at the same time with C1a and C1b. Unless the stages are exactly identical, they will not track each other.
In your case, one stage has the antenna attached to it and the other the detector. This difference will make them tune different segments of the band and at different rates. However, it might track approximately if C2ab is set to some amount of very low capacity.
We always use separately adjustable caps for two stage (double tuned) radios with the coils separated to provide light coupling. My medium quality basket weave coils performed well with an end to end spacing of about 20 cm.
If you have not tried it before, tuning a double tuned set can be a bit confusing until you get the technique.
If you attach the antenna directly to SW2b you will have a very capable single tuned set. I've tried that circuit before. It worked fine but mine was subject to a lot of short wave stations riding in on top of the MW stations.
If you take a look at various proven circuits first, you could modify your test setup so that it can copy those circuits. Then try them all and note the differences.
Edited by - Garry Nichols on 11/12/2012 7:26:06 PM
Edited by - Garry Nichols on 11/12/2012 7:36:41 PM
|_J_||Posted - 13 November 2012 1:16 |
We are having a server problem. I don't think Richard expected you of harming anyone, but the site may not have been all yours. Or? Anyway...
So, before commenting, I would like to understand better. Do you intend to switch parts in and out, are all switches shown?
Since there is probably a price to pay (in performance & efficiency for unused stuff) I would like to better understand your objective?
|neazoi||Posted - 13 November 2012 6:19 |
Thank you all for your replies,
Let me try to explain how I have thought of this circuit.
Throughout the yers, I have seen on the web many crystal sets (I have actually made just two of them). Since high-Q parts are difficult and expensive to obtain, I wanted to make a set that could be able to combine many topologies in one. My basic source of topologies was a mini research on the web I have done and summarized in this page http://www.neazoi.com/xtalpage/
Now, on the circuit.
2. The two loose coupling traps are used for the same operation for DX
3. L1 and L2 are two identical autotransformers (with all the matching benefits) variably coupled together. with the relevant capacitors, they form a bandpass filter when SW1a is switched on (as shown) in inductive mode. Varying the coupling between the autotransformers, vary the bandwidth of the filter and the selectivity.
* The point of the antenna and the detector connection on these coils should not affect the band or the frequency of the tuned circuit, but only the impedance point
4. By making different connections on the switches, different topologies could occur, for example connecting the diode on the top of the tuned circuit or...
5. My intention is to make a multi-band set. This means that there must be capacitor taps on the autotransformers as well as the traps.
6. In order to use the minimum switches possible, multi-pole switches must be used. This implies that all the coils (autotransformers and traps) and capacitors must be identical. This will ensure that the "BAND setting" will refer to all of these circuits simultaneously.
7. The autotransformer's capacitors is one dual gang capacitor, with trimmer capacitors in each gang, that help matching of the tuned circuits (because the coils could be difficult to match)
8. The rest of the capacitors are dual gang identical ones, but only the one gang is used. This is to ensure that when switching is done between inductive and direct coupling (sw1a), the receiving frequency does not change.
9. Sw1b is used to cut-off one part of the variable capacitor, si that when being in direct mode, the first autotransformer does not behave like a loose coupled trap, that ****s energy from the second tuned circuit (both of them are tuned in the same frequency).
* I do not know if the first autotransformer, connected on the ground in one end and with the other end floating, if it will **** energy out of the tuned circuit, this is something I need to verify as well.
* you have also mentioned changing in frequency when switching the diode and the antenna to different points on the autotransformers, is this the case? I thought frequency only depends on the tuned circuit, not the impedance matching point.
* I have also read that many taps will kill the coil's Q. I will use basket weave coils, but the circuit has many taps, would this be effective at all?
*Maybe I should better use separate switches instead of a single multi-pole one for the bands setting?
Some technical points will arrise, for example of how to make the coupling with so many taps...
|neazoi||Posted - 13 November 2012 6:47 |
Reading on your previous reply better, I think a split circuit ( a circuit split in more than one breadboards) with separate switches may make the situation much easier, as will allow for different coupling configurations between coils.?
|homebrew||Posted - 13 November 2012 6:50 |
A lot of twisted eyelet taps will lower the coil Q a noticable amount. Designs that allow taps to the straight wire work better.
After working with the set a while you will find that there are a few taps used most of the time. You can then copy the coil with only the best taps.
The best design for experimentation and multiband sets is to use plug in coils.
|neazoi||Posted - 13 November 2012 7:0 |
In some points taps could not be avoided though :(
for example at the diode or antenna matching.
Do you think the technique that uses an aligator clip is better, instead of flooding the coil with many unused taps?
Thankfully, basket weave coils, when made out of solid wire, allow easy clipping of the aligator without altering the coil shape.
|homebrew||Posted - 13 November 2012 8:45 |
Alligator clipping the bare wire without the twist and eyelett is definitely better.
Switches are lossy and the tie in wires cause losses.
Edited by - homebrew on 11/13/2012 8:51:13 AM
Edited by - homebrew on 11/13/2012 8:59:47 AM
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