Q: When I run an intermod study, one of the intermod products that I can calculate by hand does not show up. Is this an error?

A: The way you setup the transmit and receive frequencies, and the parameters you specify will affect the way the TAP Intermod program treats the frequencies.

In the intermod data base you sent, the following records are included:

As you pointed out, 11115 + 10955 - 10755 = 11315, and this is an A+B-C product that is within the protected offset you specified for the 11325 frequency.

With the database set up like this, the assumption is that the frequencies are paired together, i.e., 10755 and 11325 are a TX/RX pair.

In the data base, none of the "Full-Duplex" options were checked. The program therefore assumes that the paired frequencies are operating in SIMPLEX mode (push-to talk, same frequency) or HALF-DUPLEX mode (push-to talk, different frequencies). In either of these scenarios, a transmitter can never interfere with its own paired receiver. In FULL-DUPLEX mode (simultaneous conversation on different frequencies), a transmitter can interfere with its paired receiver.

Therefore, if these actually are paired frequencies, you can mark them as FULL-DUPLEX using the checkbox for each row in the data base.

If they are not paired frequencies, you can enter separate records for the TX and RX frequencies (so the program does not take them as paired frequencies). Then the data base for the intermod study would look like this:

In either case (marked as FULL-DUPLEX, or separate, non-paired TX and RX records), when you run the study the 11315 product shows up.

(If they actually are paired frequencies and are not FULL-DUPLEX, then the 11315 product should not be of concern, since the 10755 transmitter will never interfere with its paired receiver on 11325.)

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