Yes, Band Plans Do Matter

I came across an interesting example of interference on the ham bands. One of the satellite operators noticed a strange signal on the AO-51 satellite and wrote this on the AMSAT email list:


I just thought I’d relay a bit of QRM I observed on AO-51 on this morning’s 3/16/2011 1322z pass. The bird was totally quiet (just a nice carrier) for the first 5 minutes of the pass, but then it sounded like a repeater was getting into the sat uplink:

3/16 1327z: “Connected, KD7xxx repeater.”
3/16 1328z: “KD7xxx repeater disconnected.”
3/16 1328z: “hey Stacy did I see you at the corner there by Wendys?”
3/16 1330z: “…repeater in Middleton, Idaho.”

I obscured the KD7 call sign to protect the innocent. A little searching on the internet by some of the AMSAT folks revealed that there was an EchoLink station that matched the KD7 call sign.

Patrick WD9EWK/VA7EWK wrote (again, I obscured the call signs):

And there is an Echolink system (KD7xxx-R).

What may be more interesting, after some Google searches, is a series of references I saw where the KC0xxx-L system had been linked to the KD7xxx-R system. On now (1839 UTC), I saw this for KC0xxx-L:

KC0xxx-L   Clay Cntr,KS 145.920 (1)   ON   01:27   367513

In the station description, it shows 145.920 along with the QTH in Kansas. This may be the system that’s causing the QRM on AO-51, and the other system is just linked to KC0xxx-L at that time.

So it turns out that the KD7 call sign heard was linked to the KC0 EchoLink station which was operating on the uplink frequency of AO-51. George, KA3HSW, sent the KC0 operator an email and reported back that the KC0 station “has graciously changed frequencies.”

What can we learn from this?

  • Check the VHF band plans for your area before getting on the air. Be extra careful when setting up stations such as EchoLink or similar system that transmits frequently.
  • Be aware that there are amateur radio modes that you can interfere with even though you don’t hear anything on frequency. In the case of the AO-51 interference, the satellite hears the uplink frequency over a wide geography but never transmits on that frequency. The downlink is on the 70 cm band.
  • Note that the first call sign associated with the interference (KD7xxx) was not at fault. It would have been easy to jump on his case and chew him out for transmitting on the satellite uplink frequency. Showing good judgment, the satellite guys investigated further.
  • The issue was resolved by a polite (I assume) email to the offending radio amateur and he agreed to change the frequency of the EchoLink station. Nicely done.

So check the band plan for your area and follow it. And proceed with caution when interference does occur. It was a rookie error to put an EchoLink station in the satellite sub band and it was quickly resolved.

For more information on 2 Meter band usage, see this Choose your 2 Meter Frequency Wisely.

73, Bob KØNR