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Old 12th Oct 2016, 2:37 pm   #21
richard.cs
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Default Re: Airband Kit

I bought one too. Has anyone managed to find a good copy of the schematic? The only version I've found is 1000x1000 in size and covered in jpeg artefacts to the point of being nearly* unreadable. The kit comes with no documentation and something is needed to convert the component IDs on the silkscreen to something meaningful.

*I think I can make everything out, so it's probably "good enough" but it's hard to work with.
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Old 12th Oct 2016, 6:03 pm   #22
veedub565
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Default Re: Airband Kit

Steve posted a link earlier in the thread with a much better copy of the schematic.

Some of the chinglish is a bit difficult to decipher though. Regards the ceramic filter it says not to install error and seems to indicate that it is polarity sensitive, but I didn't think it mattered which way around they went.

My LO also seems to be running below the frequency I want to listen to, rather than above, it tops out around 125MHz. Again the instructions seem to indicate it should run from 120-150MHz Maybe I have my ceramic filter backwards.
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Old 12th Oct 2016, 8:28 pm   #23
richard.cs
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Default Re: Airband Kit

I'm not sure how I missed that, I thought I had read the whole thread.

Regarding the LO I plan to make quite a lot of changes anyway. Given the drift everyone mentions it'll probably end up with some sort of frequency locked loop. Toying with some microcontroller stuff at the moment. It's likely to get a low noise amp up front and some tighter IF filtering as well.

I'll build it as-designed first though and see how it is.
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Old 30th Oct 2016, 10:09 pm   #24
richard.cs
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Default Re: Airband Kit

I am about half-way through construction and have spotted a trap for the unwary. D2 and D4 are listed as AS119, which is not a valid diode part number and some chatter online suggests it's a typo for AA119, a gold-bonded germanium diode. Datasheet: https://www.digchip.com/datasheets/p.../AA119-pdf.php

What is actually supplied with the kit, or at least the one I have, is one 1N4148 and one mystery diode in a slightly larger glass case than the 4148 and entirely without identifying markings. This mystery diode measures 0.20 V forward on my multimeter suggesting it is either germanium or a low-Vf Schottky. D2 is the detector so fit this diode as D2 and use the 1N4148 as D4. D4 is part of the squelch circuit so is fairly uncritical.
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Old 30th Oct 2016, 10:50 pm   #25
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Default Re: Airband Kit

AA is the Mullard designation for a germanium signal diode, and S is next to A on many keyboard layouts, so it's an easy mistake to make. They probably realised during the run that a generic Silicon diode could be used in the other position, and adding an extra SKU worked out more economical than wasting an expensive Germanium device doing a job that could be done by a much cheaper one. Given the amount of care they evidently took over the original instructions, letting an obvious typo through, it's hardly surprising they did not bother to reprint them, or even add a corrigenda slip .....
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Old 5th Nov 2016, 7:02 pm   #26
veedub565
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Default Re: Airband Kit

I replaced D2 and D4 for something with a slightly lower bias voltage, although changing the detector diode (D2) seemed to cause some problems so ended up putting the original back in.

I also changed the value of R12, think I put something like a 500k resistor in instead.

This appears to have improved the squelch and volume somewhat, with that 1M resistor in it seemed to be overdriving and clipping the audio a bit.

I've mounted my kit in an old metal project box, with speaker, 10k 10 turn tuning pot, vol, squelch pots, DC jack, bulkhead BNC, all salvaged from scrap equipment. I've just added a £6 LCD, got the IF programmed, and looking into an emittor follower buffer amp to connect it up with so I don't load the osc. Does this look like it will be ok?

http://circuitswiring.com/circuit-di...it-Diagram.png

Edit: Oh I also changed Y1 for a 15khz one, I tried 7khz and it sounded great when you got it bang on freq.... but getting it bang on enough was very difficult and of course it wouldn't stay there.
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Old 12th Dec 2016, 9:05 am   #27
nemo1956
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Default

I have made two of these kits. The MK2 version would not tune correctly at all so I got a MK 1 version with the normal coils for the filter and oscillator.
This work's fine.
So I guess the problem are the PCB conductors?

I would like to put a frequency display on to it but don't where to get one from.
Can you tell me?

Paul.
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Old 21st Dec 2016, 2:27 pm   #28
veedub565
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Default Re: Airband Kit

Hi Paul, sorry for the late reply I'm not on here that frequently.

I bought one of these from ebay

http://www.ebay.co.uk/itm/1719245788...%3AMEBIDX%3AIT

The display itself works great, but I'm having trouble with it loading the oscillator. I used the amplifier circuit in the datasheet for the display but I don't think it's high impedence enough. Either that or the wire I put on is adding capacitance and skewing the oscillator.
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Old 21st Dec 2016, 4:12 pm   #29
AC/HL
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Default Re: Airband Kit

If you subscribe to any thread (thread tools at the top of post 1), you'll get an email if there is a reply. Very useful if you're an infrequent viewer, or are waiting for a specific reply)
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Old 10th Mar 2017, 9:04 pm   #30
veedub565
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Default Re: Airband Kit

Sorry to resurrect a bit of a zombie thread. I solved the problem of the LCD frequency display loading the oscillator. Thought it might help someone else stumbling across this thread.

Instead of connecting the freq counter directly to the circuit, I used a small inductor placed near the LO and ran flying leads to the input of the freq counter. So no direct electrical connection and it picks up the LO inductivley. Works perfectly.
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