HF APRS Boat and RV Tracking Net

For 4 years, we have been operating the National APRS HF tracking frequency on 10.151 LSB (using 16/1800 Hz tones). The channel seems to provide reliable APRS coverage between 100 to about 1500 miles during daylight hours. The purpose of the channel is for tracking boats, RV's and portable stations cross country. Usually you will accumulate the full capacity of 96 APRS stations in only a few hours of monitoring. It is time to begin developing other APRS tracking channels on other bands... Notice that the MARK frequency is your actual RF energy transmitted so your DIAL frequency will depend on the exact tones of your TNC.

          10.149.2  10.151   10.1515  LSB   National HF tracking freq
           7.083.2   7.085    7.0855  LSB   Regional HF tracking nets
          14.098.2  14.100   14.1005  LSB   Recommended DX tracking freq
          14.103.2  14.105   14.1055  LSB   Packet Keyboarding freq
The 7 MHz frequency has a lot of QRM, but is good for shorter range APRS mobile during the day. Both the 10 and 14 MHz frequencies were very carefully chosen to minimize interference to all present users of the band and to provide some measure of QRM reduction to ourselves. Please note the SIDEBANDS used. These are important and here's why:

30 METERS: By using 10.151 LSB, the MARK RF energy is 1.8 Khz lower and is inside the band edge by 800 Hz. The sideband energy is down by 40 dB which meets the FCC requirements for band edge operation. We use the LSB convention in specifying the freq to be compatible with other packet channels on the band. Of course, the actual frequency is 10.149.2 FSK or you can tune down to 10.147.6 USB! If your TNC uses tones centered at 2210 Hz or 2125 Hz, then you will need to tune 510 Hz higher using LSB.

20 METERS: We have suggested 14.098.2 since it is a full 1.8 KHz below the International CW beacon freq BUT your dial freq will typically be about 14.100. Many HAMS who do not understand the LSB offset hopefully will avoid this frequency making it relatively clear channel. The real PACKET LSB freq to AVOID for the sake of the CW ops, is 14.102 +/- 500 HZ!

Recently we are seeing some APRS activity on the 14.105 LSB keyboarding frequency. APRS is a GREAT monitoring tool, to see who is on freq and who wants to chat... This frequency would be good for casual APRS DXing and new user familiarization. This will remove some of the QRM from the 10.151 LSB and 14.100 LSB tracking frequencies. In the future, we should also find a single APRS frequency on 18 and maybe 24 MHz. Any pioneers?

TUNING: To aid in tuning into an APRS HF net, I am suggesting that ONE station on each frequency be designated as the TUNE station. That station should set his HF alias to TUNE. Any newcommer on frequency that desires to lock onto that station, simply sets his UNPROTO path to go via TUNE temporarily. Then he hits several PINGS. As each Ping is digipeated bcak, he can tune his receiver right on frequency. This is the normal netting procedure, but by using the generic alias of TUNE, a newcommer does NOT have to know who the TUNE station is in order to find the exact frequency. To avoid excess digipeating, the station must remove TUNE as soon as he is finished. Others should keep an eye on the DIGI page and remind anyone that forgets and leaves TUNE in his path. It may be possible to have additional slave TUNE's on frequency (TUNE1,TUNE2), as long as they make a DILLIGENT effort to zero to each other. A new user getting no response from TUNE can then try TUNE1 and TUNE2 in turn. Obviously these other slaves should be very widely separated. On 10.151, the Naval Academy Club station has the alias of TUNE...

HF OPERATIONS: The CONTROLS-BANDS-HF/VHF command in APRS only changes the packet timing by a factor of 2 to account for the slower channel. It also will shift the TRANSMIT port on the KAM and shift the PK-232 between VHF and HF operation. For other dual band TNC's, you must do this manually using the OPS-COMM-TNC dumb terminal and your specific TNC instructions. ALthought HF is 1/4 the speed at 300 baud, it does NOT use digipeaters, so the APRS periodicity timers are only changed by a factor of 2 between bands.

Another thing it does is to change your default ALIAS from the generic RELAY to ECHO. THis is to make sure we dont get un-intentional digipeats on HF. For emergencies, of course, you can still digipeat your HF packets off of another station, but you should specify exactly who, by callsign, NOT by the generic call of ECHO.

KAM DUAL PORT OPERATIONS: When APRS is configured for HF using the KAM, AND the CONTROLS-2PORT command is given, the KAM will not only send out packets on the selected port, but APRS will also send out duplicate packets on the other port by using the ~ and | stream switch characters. Only the STATUS, POSIT, OBJECTS, MESSAGES, and ACKS are duplicated. All other packets are only sent on the selected port. For the KAM, APRS properly initializes MYalias command to ECHO/RELAY for both ports. Please do not use 2PORT while chatting on VHF! You will kill the HF band.

GATEWAYS: By assigning the generic callsign of GATE to the gateway function in the dual port Kantronics or AEA TNC's, any HF station can gate-way into the local VHF net. HF stations can probably use the VIA path of GATE,WIDE most of the time, because the slow HF operation could hardly clutter up any local VHF APRS networks. But users on VHF APRS networks should NEVER use GATE on the VHF side of their gateways except under extreme circumstances. This is because there are hundreds of times more VHF users than there are HF users and the 1200 baud users would totally saturate the HF net! Also HF stations should never use GATE,WIDE,WIDE because the packets will go TWO HOPS on every VHF network in the country and will not only cause duplication but more importantly it makes it impossible for VHF users to know where the packets are coming from! We want to keep the effect of a gateway well within the operating area of just one WIDE.

To repeat: The purpose of HF/VHF gateways is to permit VHF local area APRS nets to see the movements of nationwide RV and BOATER mobiles. For example, when I go GPS mobile, I do not want to leave my HF station running at home so my wife can follow my status. But If I send my HF mobile APRS reports via the local HF GATEway, then my wife can see me on our computer which only needs to have a VHF TNC. Please DO NOT GATEWAY from VHF through a gateway ONTO HF except under very unusual circumstances! Similarly, if you are on HF, only use ONE WIDE after the GATE so as not to clutter up everyone's VHF nets.

KAM GATEWAY SET UP: You may connect two or more KAMS, each with an HF radio on different HF frequencies. The audio of their VHF sides are tied together into a low power VHF radio on 145.79. Both KAMS run with the GATEWAY callsign of GATE so that any HF APRS packets using the VIA path of GATE will be seen on our local 145.79 APRS net. This is for bringing both HF bands onto VHF, NOT for QRMing 2 HF bands by VHFers NOR for ANY back- to-HF gating!

The HF and VHF parameters for the KAM Unproto command are separated by a slash character as follows:


To set up your KAM using the APRS UNPROTO-VIA command, you need to remember to include the second half of the command as noted above. If you omit the second half of the command, then the KAM applies the Unproto command identically to both ports. Since I want my KAM to go out on VHF via the local WIDE area digipeaters (WIDE,WIDE) but I want the HF packets to go via any HF GATEway node (GATE,WIDE), I can do that via the APRS UNPROTO command with the following: ... Enter new VIA path: GATE,WIDE/APRS VIA WIDE,WIDE Notice that APRS automatically inserts the UNPROTO APRS VIA ... for the first part of the UNPROTO command and all I have to do is type the DIGI address (GATE,WIDE here), but for the dual port KAM, that I must type "/APRS VIA WIDE,WIDE" again myself after the slash for the second half of the command (for the VHF port).

HF TRACKING DEMONSTRATIONS: To see the results of some actual APRS HF tracking events, use the FILES-REPLAY command to replay ACADEMY.HST. The boats were transmitting once every 10 minutes or so. My first HF mobile trip was over Xmas 93 holidays. When I returned 2 weeks later the file XMAS93.hst showed all that was received in Annapolis of my journey (before the computer crashed). It shows good tracking from Knoxville TN to Florence Alabama. In fact, N2CZF (then in NJ) was able to track me all day, just about everyday, for the two week period, during daylight!

Got your attention didn't I! But it is entirely possible to make such a black box for your trunk using recently published MOSFET amplifier designs and a direct conversion receiver. We need to talk the MFR's into making such a box. Why have a $1500 transceiver at risk at home to lightening or mobile to theft when a $199 box can do it?

Return to Table Of Contents

Mail comments/corrections on content to Bob Bruninga and on HTML formatting to Steve Dimse