Comments are moderated before they will appear on the website, this is a manual process and may take some time. Please be patient.
Author Name is a required field.
Email Address is optional, but without one I won't be able to contact you back. It is never shown or linked on the website. You can always just email me if you'd rather not post a public comment. I generally reply in-line with a comment rather than email you back, unless I want to discuss something in private or off topic. Please check back to see when I reply.
Website URL is optional, if supplied the Author Name will be hyperlinked to this URL.
You may use wikitext in the body, preview may be handy here. Don't worry if you can't figure them out, just give me a hint what you want linked to what and I'll do it during moderation. Wikitext is not BBcode!
Spammers: Please don't bother wasting your time scripting up posts to this form. Everything is moderated, your post will never be seen on the web even transiently, there is no way to even view it by its internal ID, it will never be indexed. I will simply delete your post in the moderation interface. If I'm your target audience you're really on the wrong track; I'll never click on a URL in your garbage. The post content is not emailed to me (and I don't use a Win32 mail client anyway), I view the posts in plain text in the moderation interface so no clever tricks of any kind will make anything you type be interpreted by anything other than me, a human. Just give up and go elsewhere please!
14th March 2013 05:11
I would like to ask you about another receiver. I hope it's not problem.
I have built the Moorabbin receiver. It requires a 1k:8 transformer. I built a matching transformer by modifying the audio transformer of a vef 242 radio.
I took care of the turn ratio, the air gap, etc. I'm sure the transformer is OK. With the transformer, I hear a terrible scream, when I not adjust the regeneration properly, and some of the stations cannot be received, only strong scream. When I use a 32 ohm dynamic headphone, (instead of the transformer) the audio quality is good, no scream, only faint whistle, but the stations are not loud enough.
Using higher impedance balanced armature headphones (instead of the transformer) the scream is louder.
How can I resolve this problem? Something is wrong with the transformer? Or with the regeneration control? Should I use the receiver with a 32 ohm headphone (with a 70 feet long wire antenna the reception is good) or it will overload the audio stage?
All the best
Richard
3rd May 2012 07:17
Backlash or hysterese can be avoided by using an emitter resistor for stabilizing the opereation point of the receiver. The emitter resistor should be adjustable and can also be used for regen control.
4th July 2011 16:11
Richard,
1000 uH is probably about 100 - 120 turns on the same core. Depends on your ferrite really. You can make it using air-cored coils, they will just be larger. Sounds like you have the ideal caps for the job. If you have access to litz wire I'd recommend using it for the coil over normal magnet wire.
Glad the elektor FM broadcast RX worked well for you.
Regards,
Alan
4th July 2011 03:26
Hi Alan!
Thank you! I have a giant 1200pF variable cap.
It need a 1000uH coil. I have a 256pf variable cap for regen. control.
I wrote formerly about the elektor fm broadcast receiver. It works very well! It is very sensitive.
Thank you very much!
3rd July 2011 20:44
Richard,
You'd need to add turns to the coil to cover LW. It tunes to about 530 kHz at the moment. The polyvaricon has about 210 pF maximum capacity, so the inductance is about 430 uH. To hit 150 kHz with the same capacitance you'd need 5.3 mH! Inductance scales with the square of turns, it is 70 now, so you'd need about 253 turns (if I got my maths right)...
You might do better with a bit of fixed capacitance across the inductor, but that will limit your tuning range of course. Also, the parasitic capacitance of the windings will probably mean you need less turns. The six turn tickler can be increased in the same ratio, say 20 turns as a starting point.
Of course if you have larger variable capacitors available you can use them. My VFO calculator is useful for estimating this kind of thing.
Regards,
Alan
23rd June 2011 19:41
Hi Alan,
Can this device receive the longwave band (over 160 kHz) or it need to be modified? What is the value of the regen cap?
Thanks and Regards,
Richard
8th November 2013 07:45
Mast wrote...