Parts List/Tune Up Info

ManualsBrandsHitachi Kokusai Electric America ManualsElectronics6600W/5700W ATSC 1.0/3.0 Transmitter System

REV A — 25 April, 2019

Technical Service Bulletin 190425

RF Tuning Procedure for Transmitters Using Exact V2 Exciter

The Comark Exact exciter has a very capable / powerful non-linear digital pre-corrector con-

tained in it. Knowing how to set up and properly adjust this corrector is key to the best perfor-

mance and safe operation of a transmitter. Described below is a basic guide to allow a user to

accomplish the proper tuning adjustment of this corrector.

1. Overview Panel

First insure that the transmitter is properly connected to the output mask lter and load. Ensure

that you have RF output couplers in the path before and after the mask lter for transmitter feed-

back to the Exact exciter. Log into the Exact Exciter’s webpage and congure the correct output

modulation type, bandwidth, and frequency in the RF Output Parameters tab.

2. Basic Setup

On the rear panel there are 2 SMA connectors labeled FBA (Feed Back Amplier), and FBF

(Feed Back Filter).

The FBA signal should come from the transmitter output sample before the mask lter. This is

used for non-linear (shoulder) correction.

The FBF signal should come from the transmitter output sample after the mask lter. This is

used for linear (SNR) correction.

These signal levels should be in the range of -15 to -5 dBm.

3. Connecting Feedback Signals

Fig. 1 Rear panel

Summary of content (4 pages)

PAGE 1
Technical Service Bulletin 190425 RF Tuning Procedure for Transmitters Using Exact V2 Exciter 1. Overview Panel The Comark Exact exciter has a very capable / powerful non-linear digital pre-corrector contained in it. Knowing how to set up and properly adjust this corrector is key to the best performance and safe operation of a transmitter. Described below is a basic guide to allow a user to accomplish the proper tuning adjustment of this corrector. 2.
PAGE 2
Technical Service Bulletin 190425 4. Checking the Feedback Signals Levels Once the feedback signals are connected, the user can check, in the Exact Precorrections Menu, that they are properly wired, synchronized, and that their power levels are in accordance with the specifications. Fig. 2 Exact Precorrections screen 5. Connecting Feedback Signals The only parameters that need to be set before launching the DAP are Crest Factor, Protection Clipping, and Timer (Correction Time). 6.
PAGE 3
Technical Service Bulletin 190425 7. Protection Clipping Setting cont. correction has run, it should be adjusted down by 1dB from where it is set to see if there is a performance impact. If not, then leave it alone. It should only be carefully increased in small increments to see if increasing has any positive effect on signal performance. Essentially, it should be adjusted only as high as necessary to achieve acceptable performance. Fig.
PAGE 4
Technical Service Bulletin 190425 10. Crest Factor Optimization Parameter Setting For a given “Crest Factor”, the “Crest Factor Optimization” enhances the signal shoulders. Finding the best value for this parameter allows the user to gain performance on the shoulders of the signal, thus optimizing the amplifier power. This shoulder optimization involves a MER / SNR performance reduction. The user must find the best trade-off for shoulder performance vs. MER/SNR performance.