Yes, I can totally understand your concern! Since there are many variables to the "adding an amplifier" concept, I would first look at a few simple aspects before doing it to make sure no possible issues would arise.
If you were going to add any type of amplifier (voltage related) I would:
- Confirm that you have correct AC present (use a TRUE-RMS voltmeter). A standard AC voltmeter will read about 6V to 7V higher and be misleading.
- Confirm that the AC power supply that feeds this location is not overloaded and within the limits to be able to handle the extra load.
- Confirm that the POWER INSERTER being used has been "LOAD BALANCED" within acceptable design parameters. For example, if you have a 10A load at the PS, the PI should have 5A on one side and 5A on the other or something close. To have 9A on one side and 1A on the other is incorrect and will cause excessive AC votage drop at the furthest point on the 9A side.
- DO NOT just add a SAII or SAIII (or GNA) to a trunk run that was designed for Magnavox trunk amplifiers (6-T or 8-T with the motherboard) or the old Scientific-Atlanta Slimline (suitcase amplifier with wiring harness). The SAII, SAIII and GNA are nothing more than 3-output line extenders with different distortion parameters and were limited to a maximum of 6-8 deep worse case. This would be the same as adding a line extender in the middle of a trunk run, a big no-no. The older trunk stations mentioned above had 2 different amplifiers with specific distortion designs associated with each. The trunk was ran at a lower RF level with interstage tilted amplifiaction to control CSO and CTB that allowed extended trunk cascades. When the feeder was needed, a bridger amplifier had approximately 15dBmV higher output and was limited to another 2-3 line extenders past this point to control the distortions that degraded the signals carried to the customer. In many instances any 2 LE's in cascaded were "derated" by 3dB to maintain the distortion content.
- If you are using the old "SA Slimline" be sure to NOT OVER-EQUALIZE the input! The biggest problems with these animals is the absence of the interstage "P3 Filter". This is an interstage equalizer that MUST be installed for optimum efficency and minimal distortions created by the amplification process. SA charged extra for this equalizer as the trunk stations were sent with a "jumper" in that slot. Hence, the technician would instal an input EQ 21dB (without a P3 Filter) and over equalize the input signal causing excessive noise and grainy low-band pictures. If the P3 Filter was used, the input equalizer would be a 12dB and problem solved! These amplifiers have been around since the 1980's and there are many systems that have not done this.
Good luck!
Greg Tobin
