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Old 17th Mar 2004, 6:45 pm   #1
johnmarshmanathome
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Default fm to mw modulating project ?

Chaps

It would be nice to take the o/p of a decent fm tuner and induce it into the old sets. Well I have tried - using the heathkit sig gen but the quality is rubbish (tinny and distorted)

Is there a suitable circuit diagram posted on a website somewhere ?

Best Regards John
 
Old 17th Mar 2004, 6:55 pm   #2
TrevorM6TSE
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Default Re: fm to mw modulating project ?

I know that http://www.6V6.co.uk do a gadget called the gizmo that does the job. I believe it may have been reviewed on this site??
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Old 17th Mar 2004, 7:33 pm   #3
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Default Re: fm to mw modulating project ?

John,

ther was a design published in RadioBygones, Issue 18 page 6. I can probably scan it and send it if you don't have the mag.

Jim.
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Old 17th Mar 2004, 8:17 pm   #4
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Default Re: fm to mw modulating project ?

Paul has done a review of two modulators. See http://www.vintage-radio.com/reviews/modulators.shtml.
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Old 17th Mar 2004, 8:45 pm   #5
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Default Re: fm to mw modulating project ?

Hi John

I built a few simple transmitter last year. Including one that I designed myself transmitting range about 5m using only 2 x BC108. I used what I had in the junk box. Many of the designs on the web use a audio transformer to modulate the carrier, but I did not have one. The cicuit I designed just uses a simple follower varying the supply volt to a simple oscilator. I zipped up my directory and emailed it to you.

regards Chris...
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Old 17th Mar 2004, 9:02 pm   #6
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Default Re: fm to mw modulating project ?



Gents

Thanks for taking the trouble to respond

Looks like the am03 is ideally suited, and affordable too !

Obliged too to Paul for reviewing these items !

Will mail the geezer

Cheers John
 
Old 17th Mar 2004, 9:05 pm   #7
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Default Re: fm to mw modulating project ?

Hello John,

I built one from a kit and it works very well. It compresses the audio before it modulates the RF, thus reducing the dynamic range. This is done on most AM broadcasts, otherwise the quiet passages are hardly heard if the peak audio is set to 100% modulate the carrier.

The one I built was:

http://www.northcountryradio.com/Kitpages/am88.htm

Cheers,

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Old 20th Mar 2004, 4:37 pm   #8
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Default Re: fm to mw modulating project ?

Hi Gordon,

The AM transmitter looks very impressive on the web site and might be just what I am looking for. You say it was a kit - can you just confirm what was needed to build it. Did you literally have to solder it together?

Thanks

Paul
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Old 20th Mar 2004, 6:21 pm   #9
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Default Re: fm to mw modulating project ?

If you look at the following Web site you can download the manual for the Vectronics AM modulator kit.

The manual contains the circuit and the PCB layout.

http://www.vectronics.com/vectronics...odid=VEC-1290K

 
Old 20th Mar 2004, 8:45 pm   #10
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Default Re: fm to mw modulating project ?

Hi Paul,

Yes, I bought it as a kit with a pcb supplied and all the components in a bag. Although I think you can obtain it already built. If you want more info then please send me a personal mail.

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Old 20th Mar 2004, 9:55 pm   #11
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Default Re: fm to mw modulating project ?

I like the look of the Vectronics model which I've found out is available in the UK from Waters and Stanton http://www.wsplc.com so I've ordered one.

It's slightly pricier (£29.95) than the AM03 (£20) (which I too have already). I'll let you know how it works out and how I think it compares, if you're interested.

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Old 21st Mar 2004, 7:16 pm   #12
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Default Re: fm to mw modulating project ?

Thanks. Steve - how well does the AM03 work? I would be interested to know about the other you have ordered. They are both quite a bit cheaper than the North Country Radio one.

Thanks

Paul
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Old 21st Mar 2004, 7:47 pm   #13
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Default Re: fm to mw modulating project ?

The AM03 ( as seen in Paul's review http://www.vintage-radio.com/reviews/modulators.shtml) is supplied only as an assembled circuit board, with instructions. You need power (I used a battery holder for four type AA's) You also need a case and a switch. In addition I also used a couple of 4mm sockets for the aerial wire.

I found it annoying that the LED was mounted on the board - which means you can't see it inside the box. I demounted this and mounted it into the box lid.

It seems fussy about the aerial it uses and I've only had a range of a few feet out of it, but I understand there are others here that have put a " proper " aerial on it that improves it's range. That said, the quality of the output is fine. It seems to last a good while on one set of batteries, but I guess a little regulated PSU would be better for more permanent usage.

Steve J
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Old 21st Mar 2004, 9:02 pm   #14
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Default Re: fm to mw modulating project ?

I long wire laid around the loft works well as an aerial. I have good reception everywhere upstairs and adequate reception downstairs. There is details of a tuned aerial circuit in the instruction leaflet which should give a worthwhile improvement, but I haven't built this yet.

As Steve says, the sound quality is very good. I am listening to Saga on my Wartime Civilian Set, rebroadcasted with the AM02 (earlier version that came in a case) as I type this.

With the AM03 it's easy enough to move the LED onto the case, as well as the level pot and probably even the tuning cap. Such things would invalidate the warranty, but there isn't a lot to go wrong. At £20 it's an excellent starting point for your own projects.

It's a shame the AM02 was discontinued since it was a complete unit (cased, with external controls). The problem was that it cost around the same as the Gizmo, and didn't sell too well.
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Old 22nd Mar 2004, 7:26 pm   #15
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Default Re: fm to mw modulating project ?

....looking at bvws bulletins 14.3/4, Don Turner suggests a cct for modulation using a mixer valve…. tempted by this, I lashed the audio into the relevant grid of a kb minuet, and nailed a capacitor to the anode, and thence to the aerial socket of the melody maker ….and the job was seen to be a good one…quality of reception quite ok considering the outlay !….a pause for thought….greater love hath no little wireless than in laying down its life for its brethren…I think a minute’s silence is in order.

john
 
Old 27th Mar 2004, 4:36 pm   #16
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Default Vectronics AM Transmitter update..

Well, I received the kit mentioned above and if you would like to see my view, it's available on my web site here :-

http://www.aptg27.dsl.pipex.com/vect...ransmitter.htm

Hope you find the " review " useful.

Steve J.
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Old 27th Mar 2004, 5:02 pm   #17
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Default Re: fm to mw modulating project ?

Thanks for the comprehensive review Steve.

How do you think it compares in audio quality with any other similar devices?
 
Old 27th Mar 2004, 5:29 pm   #18
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Default Re: fm to mw modulating project ?

I think it's better than the AM03, but that may be down to me not rigging up a proper antenna. Other people have reported better performance than me on the AM03, probably because they are using a better antenna arrangement.

The Vectronics seems less fussy to me.

Steve J
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Old 27th Mar 2004, 6:23 pm   #19
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Default Re: fm to mw modulating project ?

Steve,

excellent review,thank you! Did you try it on different frequencies - or are you very constrained by existing stations in your part of the country?

Jim.
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Old 27th Mar 2004, 6:41 pm   #20
Steve_Johnson
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Default Re: fm to mw modulating project ?

Jim, thanks.

I haven't tried it on the different ranges. I found a quiet spot at just below 600kHz and went with that. That tends to be the quieter end of the band around here.
750kHz upwards is a bit busier.

Steve J
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