Technical information

Instruments
RETURN LOSS
Antenna systems work best when the impedance is the same at all points in the system. Impedance variations introduce signal reflections that
reduce the efficiency of the distribution system. This reflected signal meets signal travelling in the opposite direction, causing standing waves.
Measured standing waves are known as Return Loss. It is the same as Voltage Standing Wave Ratio, abbreviated to V.S.W.R., or S.W.R.
Poor Return Loss reduces signal quality and can be caused by any component in the distribution system.
An ideal V.S.W.R. is 1:1 where no power is reflected, but this is seldom attained. In practice 1.5:1 is more common, with 2:1 an acceptable limit.
Return Loss or VSWR is an important factor in delivering Digital TV with the least possible reduction in Signal Quality between the Antenna and the
Wall Socket.
Band Channel Vision 1st Sound Limits Cent. Freq.
VHF 0 46.25 51.75 45-52 48.5
1 1 57.25 62.75 56-63 59.5
2 64.25 69.75 63-70 66.5
VHF 3 86.25 91.75 85-92 88.5
2 4 95.25 100.75 94-101 97.5
5 102.25 107.75 101-108 104.5
5A 138.25 143.75 137-144 140.5
VHF 6 175.25 180.75 174-181 177.5
3 7 182.25 187.75 181-188 184.5
8 189.25 194.75 188-195 191.5
9 196.25 201.75 195-202 198.5
9A 203.25 208.75 202-209 205.5
10old 209.25 214.75 208-215 211.5
10new 210.25 215.75 209-216 212.5
11old 216.25 221.75 215-222 218.5
11new 217.25 222.75 216-223 219.5
12 224.75 229.75 223-230 226.5
Band Channel Vision 1st Sound Limits Cent. Freq
UHF 28 527.25 532.75 526-533 529.5
4 29 534.25 539.75 533-540 536.5
30 541.25 546.75 540-547 543.5
31 548.25 553.75 547-554 550.5
32 555.25 560.75 554-561 557.5
33 562.25 567.75 561-568 564.5
34 569.25 574.75 568-575 571.5
35 576.25 581.75 575-582 578.5
AUSTRALIAN TV CHANNEL DESIGN & LIMITS
New channel 10 and 11 services will be placed +1MHz.•
Digital services can be offset +125KHz from •
centre channel.
Stereo sub-carriers +242KHz from 1st Audio carrier.•
No new television services for channels 3, 4, 5, or 5A.•
Band Channel Vision 1st Sound Limits Cent. Freq
UHF 36 583.25 588.75 582-589 585.5
5 37 590.25 595.75 589-596 592.5
38 597.25 602.75 596-603 599.5
39 604.25 609.75 603-610 606.5
40 611.25 616.75 610-617 613.5
41 618.25 623.75 617-624 620.5
42 625.25 630.75 624-631 627.5
43 632.25 637.75 631-638 634.5
44 639.25 644.75 638-645 641.5
45 646.25 651.75 645-652 648.5
46 653.25 658.75 652-659 655.5
47 660.25 665.75 659-666 662.5
48 667.25 672.75 666-673 669.5
49 674.25 679.75 673-680 676.5
50 681.25 686.75 680-687 683.5
51 688.25 693.75 687-694 690.5
52 695.25 700.75 694-701 697.5
53 702.25 707.75 701-708 704.5
54 709.25 714.75 708-715 711.5
55 716.25 721.75 715-722 718.5
56 723.25 728.75 722-729 725.5
57 730.25 735.75 729-736 732.5
58 737.25 742.75 736-743 739.5
59 744.25 749.75 743-750 746.5
60 751.25 756.75 750-757 753.5
61 758.25 763.75 757-764 760.5
62 765.25 770.75 764-771 767.5
63 772.25 777.75 771-778 774.5
64 779.25 784.75 778-785 781.5
65 786.25 791.75 785-792 788.5
66 793.25 798.75 792.799 795.5
67 800.25 805.75 799-806 802.5
68 807.25 812.75 806-813 809.5
69 814.25 819.75 813-820 816.5
AMPLIFIER MAX. OUT. & RULES OF THUMB
As more channels are amplified, an amplifier’s maximum output level must be reduced to stop intermodulation products reducing picture quality.
Broadband amplifiers are usually rated for maximum output with 2 equal channels of say 108dBμV. This is the figure to reduce according to the
number of TV channels being amplified. Count 88–108MHz band 2 F.M. radio as 1 channel unless it is 10dB or more below the TV levels.
No. of channels 2345678910
Reduction indB 0 2.5 3.5 4.5 5 5.5 6 6.5 7
No. of channels 123456
Reduction indB 0 3 4.5 6 7 7.5
Example: Using an amplifier with a manufacturers maximum
output rating of 108dBμV when amplifying 8 equal channels, the
second amplifier should have it’s maximum output level calculated
108 -(6+3) = 99dBμV
The noise an amplifier generates adds to the total noise in a system, so
the maximum output level must be further reduced according to the
number of amplifiers being used.
TECHNICAL INFORMATION
Catalogue 106
102