UV Pager

Each memory channel gets a pager mode, set in CHIRP:

On a watched page:

• the backlight comes on;
• the department's name is shown, inverted, over the main screen until EXIT;
• the green LED blinks;
• three beeps sound once the tones are over.

The beeps wait because stacked pages follow at once, and a beep in the middle would cut off the next department's A tone. EXIT acknowledges the page and returns a Silent channel to quiet.

The watch list holds up to 150 departments. Each one has a name, an A tone, a B tone (or a single long tone), minimum lengths and a tolerance.

Sellers mislabel these radios. Look for "V3" or "UV-K1" in the listing. Listings that say "UV-K5(8)" or "K5(99)" are usually the older V1 board.

While a pager channel is receiving, a hardware timer samples the receive audio at 9.6 kHz. The audio is picked up before the speaker amplifier, so a Silent channel can be decoded with the speaker off. When the channel isn't receiving, the sampler is stopped and the radio's power saving is unchanged.

1. Zero crossings. The decoder times rising zero crossings to 1/256 of a sample, using hysteresis and linear interpolation. Only rising-to-rising periods count, so CTCSS under the tone and DC offsets cancel out.
2. 40 ms blocks. A block counts as a tone when its periods agree to within a quarter period and its level clears a gate. Its frequency is periods ÷ time.
3. Segments. Consecutive blocks within 1.5% of each other join a segment. Averaging them gives the precision, and a segment survives one bad block.
4. Matching. A page is an A segment of at least its minimum length, followed straight away by a B segment of at least its minimum, each within tolerance (2%). A long tone is a single long segment. A tone that completed one page can't also be the A of the next, which avoids false pages when pages are stacked.

All the arithmetic is 32-bit integer. The whole feature adds about 2.9 KB of flash and 128 bytes of RAM to the firmware, and the watch list is read from flash.

1. Flash the Pager build with UV Studio (web-based; works in Chrome or Edge over the programming cable). Back up your calibration first: UV Studio does that too.
2. In CHIRP, use File → Load Module to load the Pager driver. The radio model is UV-K1 & UV-K5 V3 (F4HWN Pager).
3. Download from the radio. In the Pager tab, set the monitor time, beeps on or off, and up to 150 departments.
4. On the dispatch channel's memory, set Extra → Pager to Alert or Silent, then upload.

If you keep your departments in tones.cfg files (INI sections with atone, btone, lengths, tolerance and description), a script copies them into a saved CHIRP image. It reads only the tone fields:

The watch list is stored with the radio's other settings, so it moves with the firmware's multiboot config banks. A radio without the Pager edition simply ignores it.

The V1 radios (UV-K5, UV-K5(8), UV-K6, 5R Plus) can't sample audio, so this build hands the job to the BK4819 chip. Its SelCall detector holds 16 programmable tones and reports which one it heard. The firmware times those reports and matches them to the watch list with the same A-then-B rules. The build fits in the V1's 60 KB by leaving out the spectrum analyzer, FM radio, AirCopy and screenshots.

• Marking channels. V1 has no spare channel bits, so the channel name decides: a name starting with * is an Alert channel and one starting with ! is a Silent channel. That works with stock CHIRP or on the radio.
• Watch list. It is built into the firmware and limited to 16 distinct tones, which is enough for several departments.
• Accuracy. The chip places each tone with an 8-bit coefficient. Above about 600 Hz that is fine, but below it neighbouring QC2 tones look the same to the chip: 349.0 and 368.5 Hz differ by one step. Its bandwidth is undocumented, so neighbouring departments may be confused. The table generator warns about tones it can't separate.
• Timing. The chip says which tone it heard but not when the tone ends, so the B and long-tone lengths are measured from the first detection. The beeps wait until the transmission ends.
• On-air readout. On a pager channel, the bottom of the screen shows each detection, for example PG 707.3 x3. The first real pages will show how the chip behaves.

Flash it with uvtools (web-based; Chrome or Edge), after backing up the EEPROM and calibration. If the detector proves too coarse, the fallbacks are a small hardware audio tap to a spare ADC pin, or the V3 radio.

• Input level. In normal receive, the audio level reaching the ADC follows the volume setting, so the level gate may need tuning.
• Low tones. The radio's 300 Hz high-pass stays on in this edition, so QC2 tones between 321 and 433 Hz arrive weaker. The decoder doesn't depend on level, but this is unconfirmed.
• Beeps during receive. The radio has to come back to receive cleanly afterwards.
• V1 detector. Whether it reports a tone once or repeatedly, how selective it is, and its threshold.
• Battery saver and dual watch. Either can make the radio miss the start of an A tone. Turning them off on a pager channel may be the answer.