Icom 207 for Packet

I’ve had a play with the Icom 207 packet mode and have found two possible problems or undocumented features depending whether you’re buying the radio or selling it I guess.

The packet/data interface is implemented as a 6 pin mini-din socket and presents a single transmit audio path, a single ptt line and two receive audio paths which, according to the manual, are for 1200 baud packet and 9600 baud packet.

The 1200 baud audio output is de-emphasised audio and is controlled from the squelch circuit so if mute is closed then there’s no audio. The 9600 baud audio output is buffered demod audio and is present regardless of the mute settings.

And now the fun part. The same audio input is used both 1200 baud and 9600 baud packet and the audio is treated differently depending on whether the bps menu setting is set for 12 (1200 baud, emphasised and amplified audio) or 96 (9600 baud, unemphasised audio).

Having set up a kantronics kpc3 with this radio with a 3.3k series resistance to protect the radio input and feeding the ic207 rf output into a deviation meter, the following results have been obtained.

NOTE: the only change in the test setup was to change the bps setting from 12 to 96. This was done several times just to make sure the results are repeatable and that I wasn’t crazier than normal.

tx deviation

bps

low tone

high tone

12

6.1kHz

6kHz

96

3.3kz

3kHz

Yes, the low tone deviates more than the high tone!

And now for the extra gotcha, which is documented in the manual but WHY it’s done escapes me!

With the bps setting at 12 (1200 baud packet) the ptt signal on the 6 pin mini-din data connector (signal pttp) does NOT mute the mic on the front panel, so you can get live mic problems with 1200 baud packet if you’re not careful.

Read this bit twice. With the bps setting at 96 (9600 baud packet) this same ptt line (the pttp signal) DOES mute the front panel mic. Just for fun I checked the circuit and yes the pttp signal on the data connector and the microphone ptt signals are separate signals.

Warren Stirling VK3XSW 30 Dec 2003

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