MiniMod pantry transmitter
3 Attachment(s)
Just a quick mention of the MiniMod, a micro-power pantry transmitter that appeared in the Winter 2011 BVWS Bulletin, that I've just finished building.
This is an elegant little circuit that performs brilliantly, and the audio quality is excellent, so congratulations must go to the designer Ian Liston-Smith. I built mine on a piece of matrix board less than 2" square and housed it in a Maplins plastic case, the most expensive item in the parts list! The specified coils are still available from Spectrum Communications for 90p each. I had most of the passive components in stock or donated by friends, and I only had to buy a 2N3819 plus the coils. All told, I don't think the cost exceeded £10. Apart from having to trace and rectify one wiring error :-] it worked first time. I added an LED indicator fed via a resistor and five diodes to give me an "on" warning light and battery state indicator, which goes out below about 5 volts. The output is good enough to cover one or two rooms with five feet of wire as an aerial. A couple of photos are attached. Phil |
Re: MiniMod pantry transmitter
Hi Phil.
Many thanks for posting that - it's always good to get feedback, particularly if it's good! The two identical coils should be available for the foreseeable future. Although in screened miniature IF-type cans, there's nothing special about them and they could be hand wound. (Did I include details in the article for anyone who wanted to wind their own? I don't have a copy available right now.) I didn't include an 'ON' LED in the design as it would nearly double the current consumption. But a low-current flashing LED would be a good idea. I really like the label you put on yours. Very professional! White-on-black and printed on what? (The wiring error... yours or a misprint in my article? I made four spares from the published text/circuit so didn't think I missed anything...) Thanks and regards, Ian |
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Thanks again for a really good design. It compares very favourably with a professionally manufactured AM-03 which I bought some years ago. The Mini-Mod has half the component count of the AM-03 but produces just as good quality and amount of output. Kind regards, Phil |
Re: MiniMod pantry transmitter
Another positive recommendation from me too.
- Joe |
Re: MiniMod pantry transmitter
Nice to see this Modulated Oscillator getting some positive feedback........
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Re: MiniMod pantry transmitter
Hello,
I have a couple of questions: 1) I would like to build this transmitter. Would it be possible to obtain a copy of the article? 2) If the answer to 1) is yes, could someone please provide contact information for Spectrum Communications? When I Googled them from here in the USA I got links to all kinds of businesses, but not the correct one. Thanks in advance, Colin |
Re: MiniMod pantry transmitter
If you PM your email address, I'll send it. I can't remember how to attach documents that are not images via the forum email or PM system. :-[
Ian |
Re: MiniMod pantry transmitter
I wanted a flashing LED on my AM-03 Modulator as I thought it would serve as a good reminder to switch off when not in use.
Had to replace it with a standard one as I could hear the pulsing of the LED on the received audio. SR |
Re: MiniMod pantry transmitter
Spectrum are at www.spectrumcomms.co.uk
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Re: MiniMod pantry transmitter
Ian - PM has been sent.
Phil - Thanks for the info. Regards, Colin |
Re: MiniMod pantry transmitter
OK Colin. You need two coils, type 90u0L and they are a standard stock item - the shipping charges will probably exceed the price of the parts!
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Re: MiniMod pantry transmitter
It is perhaps worth pointing out that the MiniMod was described fully in Ian's excellent article, which was published in Volume 36 Issue 4, the Winter 2011 edition of the BVWS Bulletin. The Bulletin is distributed free to BVWS members, but back numbers are available direct from the BVWS at reasonable cost.
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Re: MiniMod pantry transmitter
Phil,
I didn't think to ask if back issues of the bulletin were available, as in my previous experiences with other clubs this service was not provided. BVWS is obviously a cut above the rest! Thank you for pointing it out, I will visit the website. Regards, Colin |
Re: MiniMod pantry transmitter
Phil,
I visited the BVWS website, but couldn't see how to order a back issue of the bulletin. I did see the table of contents for the Winter 2011 issue and it seems to have a lot of interesting articles in addition to the MiniMod, so I'll be happy to purchase it. Would you please be so kind as to point me in the right direction. Many thanks, Colin |
Re: MiniMod pantry transmitter
2 Attachment(s)
Well, it took a little longer than anticipated, but my MiniMod is finally up and running. What an excellent design. I have to thank Ian not only for designing this in the first place, but also for sending me a copy of the Bulletin article and the ExpressPCB layout, which helped me tremendously with the construction. Very much appreciated. I attached a couple of photos.
Cheers, Colin |
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Nice work, Colin.
I have just put together a collection of parts to make another MiniMod, I just need an LM386. I will be using Veroboard and not going for such miniaturisation this time. A really excellent design, thanks again Ian. |
Re: MiniMod pantry transmitter
Very nice indeed and as legal as it can be.
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Re: MiniMod pantry transmitter
Hi Phil, if you are using veroboard beware of the track capacitance as it may throw you tuning well off. Perforated board is much better.
Ed |
Re: MiniMod pantry transmitter
Hi Ed. You make a valid point, but I think at these relatively low frequencies you may be worrying unnecessarily.
I have just checked the capacitance between two adjacent tracks on the 4"x3" piece of 0.1" matrix Veroboard on which I propose to build this project, and measured just 2pF. As the tuning capacitors for both oscillator and output stage are 270pF, this will swamp any stray capacitance introduced by the Veroboard, and the range of variable inductance available from the specified coils should be more than sufficient to compensate. In his original article, Ian did say that construction wasn't critical and Veroboard or other methods could be used, so I'm not anticipating obtaining an output signal on Long Wave or the 49 metre band...! :laugh1: |
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