Icom IC-2725 in mobile APRS

Icom IC-2725 can be used as mobile APRS station by connecting an APRS modem to the packet modem connector and using the right VCO in fixed APRS frequency. I am using the Tinytrack as APRS transmitter. The caveats: If you are using the left VCO in voice communications and pressing PTT at the very same time as the APRS is transmitting, the audio routes are not connected. You end up sending an empty carrier.

How to power up the GPS at the same time with the radio?

Tällä kytkennällä saa GPS:ään orjakytkettyä sähköt. Itse hukkaan tuohon vähän jännitettäkin. GPS kun on 3.7V mallia...

The transmitter noise in BC band

Icom's transmitter is not very clean. If used in a mobile, the radio will transmit some noise in BC band and thus causing a noise burst in BC radio receiving. If the BC radio is RDS radio it might start to search for an alternate frequency due to the noise interference. This is very annoying feature when the radio is used as APRS transmitter. You can filter out the noise in BC band with a shorted co-axial cable stub filter. The length of the stub from the T-branch is 300/94MHz/2*0.66=1.05m (for RG-58). If a good quality co-axial cable is used the attenuation in 145MHz is only 0.1dB and in 434MHz only 0.3 dB. The attenuation in BC band is even 25dB.

Last modified: Tue Dec 6 20:18:37 EET 2005