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Homebrew Equipment A place to show, design and discuss the weird and wonderful electronic creations from the hands of individual members. |
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14th Oct 2021, 4:49 pm | #1 |
Heptode
Join Date: Sep 2010
Location: Hythe, Hampshire, UK.
Posts: 632
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Another Pantry Transmitter
Hello everyone,
I finally decided to get around to making a pantry transmitter for the radio collection in the house. I looked at a lot of different designs but in the end decided to design one myself. The attached PDF is the final circuit and with a couple of feet of wire attached covers the whole house from inside a front room cupboard. The frequency of operation is set by C5/L5 and adjusted a small amount by C9, I chose around 1MHz as the operating frequency as there are no broadcast signals on this frequency where I live. An audio input of 280mV will 100% modulate the carrier which is around 14V RMS at the output. R5 is shown as 10K which will work fine in most cases but may need to be adjusted while monitoring the output with a scope at the 'RF Out' to make sure the carrier is linearly modulated and doesn't 'flat top'. A simple 12V AC supply from a transformer is all that is need to power the unit. If you do decide to have a go at building it make sure the values of L1, L2, L3, L4 and C8, C10, C11, C12 are adhered to. If you have a higher level audio input then use a potentiometer on the AF input. All the best |
14th Oct 2021, 5:27 pm | #2 |
Moderator
Join Date: Jun 2003
Location: Oxford, UK
Posts: 27,966
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Re: Another Pantry Transmitter
Nice simple circuit. Do you get much frequency drift?
You probably already know this, but 1MHz isn't a valid AM channel in Europe, not that it matters in this case. |
14th Oct 2021, 5:30 pm | #3 |
Guest
Posts: n/a
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Re: Another Pantry Transmitter
I don't know, a pantry transmitter in a cupboard? Whatever next? I have a real pantry but my "transmitter" er. "modulator" is in the kitchen, I guess the RF doesn't mind at all.
Good job, nice and simple as said. Last edited by Guest; 14th Oct 2021 at 5:30 pm. Reason: Spelling! |
14th Oct 2021, 5:55 pm | #4 |
Heptode
Join Date: Sep 2010
Location: Hythe, Hampshire, UK.
Posts: 632
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Re: Another Pantry Transmitter
Hi Paul,
Yes I did realise that but as you said it doesn't matter in this case. it's absolutely rock solid where it is but as I haven't tried heating or cooling it I don't know what the drift would be like. |
14th Oct 2021, 7:00 pm | #5 | |
Dekatron
Join Date: Apr 2012
Location: Wiltshire, UK.
Posts: 14,007
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Re: Another Pantry Transmitter
Quote:
My xtal-controlled pantry-transmitter stealthily fits in between two 'official' channels, neither of which are currently used by any broadcaster within 500Km. "Hide in the gaps"!
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14th Oct 2021, 10:52 pm | #6 |
Dekatron
Join Date: May 2010
Location: Greater Manchester, UK.
Posts: 18,724
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Re: Another Pantry Transmitter
I used to send music round the house on 300 Meters using the 1MHz position of my Class D Wavemeter. I think I just applied low level mod to the grid (TC) of the oscillator valve.
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