Tag Archives: UZ7HO

Multimode APRS RX Setup

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System Diagram


Download aprsis32_multimode system diagram – PDF.

I’ve been experimenting with APRS on 10MHz. Mainly reception at home and also some portable operation. After spending some time with UIview32, I changed over to APRSISCE/32 which I find more suitable for my needs.

For 300baud FSK packet I use the UZ7HO SoundModem. This uses a soundcard for TX and RX and emulates the AGW Packet Engine interface. It can be configured to use two audio frequencies simultaneously and has a waterfall display to aid tuning.

Chris G4HYG has just released version 3.29 of his APRS Messenger program. Not only does this interface with a standard TNC. It also supports sending and receiving APRS traffic over PSK, GMSK and MFSK16 modes. This makes use of the MMVARI engine which he has configured to run as multiple receivers. It will also connect the the UZ7HO SoundModem but presently this only works on receive. Stephen WA8LMF has also written some extensive notes on configuring APRS Messenger and using with UIview.

APRSISCE/32 is more flexible in this respect, so I configured an additional text port to connect to APRS Messenger port 8063. In this setup, APRS Messenger is used purely as a PSK/GMSK/MFSK16 receive decoder.

Finally I bought the SCS-Tracker TNC. After placing my order back in April, I had a few months to wait due to a re-design of the enclosure. This is configured to run in Robust Packet Mode and connects to the APRSISCE/32 host using KISS protocol over a USB serial connection.

Audio Frequency Settings

  • The receiver is set to 10147.30kHz USB dial frequency.
  • A PBT offset of +500Hz shifts the top end of the audio passband up to 3kHz.
  • The HF modems in APRS Messenger are set for 2400Hz.
  • The HF modem in UZ7HO SoundModem is set for 2000Hz.
  • The RPR modem in the SCS Tracker is set for 1500Hz.

Both APRS Messenger share the same sound card. Both applications should be set for a sampling frequency of 11025kHz and the SoundModem should be calibrated for best results.

APRSCE/32 Port Settings

  1. APRS-IS – Your normal APRS Internet connection (not shown in the diagram).
  2. KISS TNC – connected to SCS-Tracker TNC via USB.
  3. UZ7HO_SM – AGWPE connection to tcp/ip port 8000.
  4. APRS_MSGR – TEXT connection to tcp/ip port 8063.


10Mhz APRS seems quite active and I’m hearing a lot of traffic on RPR, probably more than on 300baud FSK. There isn’t much PSK/MFSK activity and I’m hoping to contribite to that mode with my portable setup.

See the system diagram above (click on it for full size or download the PDF!) to see how it all fits together.

Check the Digipeater Users list at DB0ANF.