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8th February 2013 15:19
Indra,
The "A" and "O" are markings on the particular polyvaricon I used. I believe they mean "Antenna" and "Oscillator" respectively. In AM broadcast band receivers the larger capacitor normally tunes the ferrite loop-stick antenna and the smaller the local oscillator.
Regards,
Alan
12th November 2012 00:04
what is the meaning of A and O on the VC.
Thanks.
13th August 2012 11:07
Jeroen,
It is a 1N5711, but you could use 1N4148 or similar PN junction signal diodes if you can't get the schottky detector diode. You might also try germanium diodes, but they probably won't work as well as the 1N5711 with the small bias as used here.
Regards,
Alan
1st July 2012 16:11
Nice project, I would like to built this receiver by myself. What kind of diode did you use? I can only read 1N5...
Greetings from The Netherlands!
22nd July 2011 22:40
Benjamen,
I can see why you ask, the diagram is 33 k, but the picture clearly shows a red multiplier band on the visible resistor! Looks like I goofed, I'll check the circuit when I get I to the lab next. Use 3k3 for now I guess.
Regards,
Alan
22nd July 2011 18:37
Resistors in series with 10uF caps - 33K or 3.3K?
21st July 2011 23:54
Thanks that have answered my question Alan!!!!
I hope so...portable scanner would be better for 300 mHZ NFM.
Nevertheless I wish you and your site of the further development!!!!!!
With best regards!!! Alexey.
73!
21st July 2011 08:02
Benjamen,
Much better than you need, but if you have some, why not? The humble LM358 is likely cheaper and uses less current, but the battery life will be fine with just about any opamp that can take 9 volts.
In this application the amplifier is very non-critical, you might like to build it using a few transistors instead. The opamp is just a jelly-bean that makes it completely trivial to build. Using transistors you can probably use direct coupling most of the way, saving the bulky electrolytic caps, and make the device smaller and even lower current consumption.
Regards,
Alan
20th July 2011 23:52
Thank you for your answer, Alan. And what about TLC272?
20th July 2011 23:43
Benjamen,
Sure, should be just fine. The LM358 will use a little less current so the battery life might be shorter, but it should work fine. The main difference between them is the common mode range and the input bias currents. As neither are critical in this circuit it should be a drop-in replacement.
Regards,
Alan.
20th July 2011 23:20
Can I replace LM358 opamp with TL072?
3rd July 2011 20:52
Alexey,
This particular receiver can't detect NBFM. Your best bet is a cheap digital scanning receiver. They are available quite cheaply now days and most cover the 300 MHz region.
The main problem with designing an "easy" homebrew receiver for UHF is stability of the local oscillator. Modern receivers solve this with PLL synthesisers. You could multiply up a VXO crystal if you happened to have one in the right region, or come up with a mixing scheme to hit the region of interest, but the push-button entry of a digital receiver is very nice to use...
The VHF receiver is only usable because it has poor selectivity and the transmissions it seeks are amplitude modulated, which is quite easy to detect in comparison to NBFM.
Regards,
Alan
29th June 2011 01:32
Greetings Alan! My English not so, but a theme with the receiver very interesting...
I also saw the receiver Charles Wenzel's and tried it to repeat...but air lines is too distant of my home.
Whether to me is interesting your opinion... can the receiver be made such for a river range of 300-337 MHz Narrow Band FM (http://www.mobilradio.ru/information/vocabulary/freq_river.htm)
I`m interesting in 3(300,100) 5 (300,200) and 7 (336,300) channel of communications
Thanks for your attention!!!
3rd November 2010 21:09
Etherman,
The other end of that resistor goes to the positive supply rail. The two 10M resistors bias the detector diode and the opamp input near mid-rail.
Regards,
Alan
14th September 2010 06:52
Hi,
I live in an area where ham transmitters are illegal. So I just play with receivers.
I am interested in duplicating your air-band receiver, but the schematic is less clear than Wenzel's original,especially the component marked 10M with an arrow pointing upwards. It seems like a 10M resistor but I don't know where is its distal connection.
Thank you in advance.
18th August 2010 02:23
G'day Arv!
If you live really close I'd suggest building something like that crazy idea I had back in the parent article - of amplifying the entire air band at once and then AM detecting it! With this passive receiver you'd need to be pretty darn close to hear much if anything. Aircraft TX aren't the 50 kW+ monsters that TV and FM broadcast stations are... Can't hurt to try, the solderless breadboard prototype is fun to try.
I have had lots of fun over the years with super-regenerative receivers for the air band. They work especially well with the AM modulation. Of course they radiate broadband noise like nothing else which is why I used this amplified crystal set in-flight, but for listening "nearby" they work just fine. I can hear the tower approach controller in my shack with this antenna-less receiver and I am about 16 km away from the tower.
Speaking of write-ups, I need to write up the whole trip. Honestly though I was there for a month and did a whole lot of things - I am little intimidated by the effort required to do it justice.
Regards,
Alan
18th August 2010 02:05
Alan
Very interesting project, but the trip experience writeup is what really makes it worth reading. My location is near the approach path to a major airport, so I may have to duplicate your zero-emission receiver.
Arv
_._
13th August 2013 23:27
Jozsef wrote...