vhf_hybrid_repeater_from_junk
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vhf_hybrid_repeater_from_junk [2018/09/14 00:00] vk3smb created |
vhf_hybrid_repeater_from_junk [2018/09/14 00:09] vk3smb |
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| + | ====== TAKE NOTE ====== | ||
| + | This design was thought up several years ago and was never implemented past the test bench stage. | ||
| ===== Receiver ===== | ===== Receiver ===== | ||
| ==The Idea== | ==The Idea== | ||
| Line 53: | Line 55: | ||
| ==Documentation for reference== | ==Documentation for reference== | ||
| ===== Transmitter ===== | ===== Transmitter ===== | ||
| + | |||
| + | ==The idea== | ||
| + | |||
| + | The FM828 Transmitter is phase modulated. | ||
| + | |||
| + | I propose that we modify the TX for frequency modulation. | ||
| + | |||
| + | Basically, we need to feed buffered audio into the crystal oscillator at a low level (effectively 1/8 of the level that would be applied to the LO). My bet is to feed it in via varicap diodes | ||
| + | |||
| + | At the very least, we need to Frequency modulate the CTCSS tone and keep the voice PM. | ||
| + | |||
| + | ==FM Modulation== | ||
| + | Doing a google search to save re-inventing the wheel, I was going to use a PRM80 exciter and the FM828 oscillator, VK6UU had gone to the trouble 20 years ago. | ||
| + | {{: | ||
| + | ==TX Audio Processing== | ||
| + | To use this effectively these other two diagrams will need to be used. we only need 3 audio inputs - one from the RX, the ctcss out on COR and an input for the watchdog. | ||
| + | |||
| + | {{: | ||
| + | {{: | ||
| + | ==Notes on the audio board== | ||
| + | //This circuit provides some audio gain control(AGC) along with audio frequency adjustment, both high frequency (above 1khz) and low frequency adjustment (Below 1khz).// | ||
| + | |||
| + | //Obtaining good audio (sounding like the direct audio) is difficult in a voice repeater for several reasons.// | ||
| + | |||
| + | //Audio in a repeater is demodulated from being an RF signal (FM) then applied to the repeater' | ||
| + | |||
| + | //All these processes introduce some distortion and frequency response issues.// | ||
| + | |||
| + | //Also audio levels vary greatly between users, some by as much as 20dB (a lot). The repeater can introduce some audio level compensation so as to reduce this level difference.// | ||
| + | |||
| + | //However high levels of audio gain control (above 6dB) start to compress users who have levels of back ground noise (eg mobile) and the background noise level starts to e3qual the voice level, which makes for difficult to read audio.// | ||
| + | |||
| + | //Another issue is a repeater that is linked another (such as the WIA news broadcast) would add another 6dB compression to the previopus repeater' | ||
| + | |||
| + | //This ACG circuit is fairly simple and comples AGC circuits that split up the frequency segments and treat them separately can produce a very good compressed audio that can make a signal sound much louder. | ||
| + | {{: | ||
| + | |||
| + | ==CTCSS Tones== | ||
| + | I am suggesting that we fit a subtone to the transmitter only whilst the repeater is receiving a signal in (CTCSS tone in). This means we can use it for linking or control later on. | ||
| + | |||
| + | ==Control== | ||
| + | |||
| + | There needs to be a power down arrangement built in as well. preferably using a transistor rather than a relay 2N3055 comes to mind here. | ||
| + | |||
| + | ==Construction== | ||
| + | ==PCB Details== | ||
| + | I have drawn the Daughter board to go in the exciter to add audio to the crystal. | ||
| + | {{: | ||
| + | |||
| + | [[Philips FM8** Pinouts]] | ||
vhf_hybrid_repeater_from_junk.txt ยท Last modified: 2018/09/14 00:09 by vk3smb
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