Abstract: A portable HDTV testing device inserts a deterministic test signal having a frequency close to the symbol rate of the received HDTV signal. As the received HDTV signal is randomized prior to broadcast for synchronization purposes, the addition of the deterministic test signal to the randomized data signal is essentially equivalent to the addition of a random (or white) noise signal to an information bearing signal. The use of a deterministic test signal avoids the expense associated with a random signal generator, thus making possible an inexpensive and portable HDTV test device. To test the noise margin of a received signal, which is used to determine if the installation of the antenna and HDTV receiver is optimized, the test unit inserts known levels of the noise signal incrementally and measures the bit error rate until the bit error rate exceeds a known threshold above which proper decoding is not possible.