Hillsborough
Sheffield
S6 2LL
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Main Page List
Appendix
Where I put stuff when I can`t think of anywhere else to put it.......
Appendix Index
UHF Channel Numbers to Frequency etc
Polar Response Diagrams (now has its own page)
Sky Digiboxes General Information (on the RF output/loop through)
Test results (full) of Group A aerials
Test results (full) of Group B aerials
Test results (full) of Group C/D aerials
Test results (full) of Group K aerials
Test results (full) of Group E aerials
In the UK television transmissions are usually referred to by a channel number as opposed
to a frequency. Both the channel number and the frequency are given on all our Channel
Allocation Guides (e.g. the one for Crystal Palace) but the frequencies are rounded down
by 0.25MHz. For example the exact frequency for CH21 is 471.25MHz.
The table below also shows channel number v frequency (and also the wavelengths).
In the case of analogue the channel number is related to the frequency thus :
Fv = 8n + 303.25
Where Fv = Frequency of the vision carrier in MHz and n = Channel Number.
For digital the channel number is related to the frequency thus :
Fc = 8n + 306
Where Fc = Centre frequency of the MUX, and n = Channel Number.
As an approximation, good enough for most tuners, the digital frequencies are 3MHz
higher than the analogue (although it`s actually 306 -
Since most tuners use channel numbers this 3MHz difference is not usually significant, but if you are trying to enter the actual frequency to yours it obviously might be for you !
Some digital MUXES are transmitted with a channel offset and these are + or -
These offset frequencies can be found in the relevant Ofcom documents :
The vast majority of digital TVs or STBs can still tune in to a MUX even if it has an offset
and this is also the case in manual tuning. If you have trouble trying to tune in your
MUXES its always worth checking that the tuner is not being sidelined by an offset, though
this should be very rare.
Such is the Black Art nature of RF all aerial test readings are approximate, in fact
as far as I`m aware
no lab will guarantee accuracy better than +/-
It must be admitted that these particular results are less accurate than that (unlike our TV aerial tests) but they still give a pretty reliable indication of the relative performance of the various antennas.
UHF TV frequency wavelengths
To calculate the wavelength (in cms) divide 30,000 by the frequency (in MHz).
This should be accurate to 0.07%, which is accurate enough for most RF applications....
The “variable” figures result from the directional nature of the particular aerial.
This doesn`t apply to the TV aerials, they`re variable because they`re not even designed to
pick up VHF frequencies ! Note that if the 3 element aerials were pointing directly away
from the transmitter you`d probably lose more than the -
Though you would be pretty unlucky if you were to align your aerial like that !
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Accessing the hidden service menu, used for switching on RF2, and/or, altering the frequency/channel of the RF2 output.
Be very careful what options you change in these menus, particularly the satellite dish settings !
Standard box = (press) Services > 4 > 0 > 1 > Select
Sky HD box = Services (options menu) > (highlight “Settings”) Select > (highlight “Picture”, then
press) 0 > 1 > RF Outlets > Select
The modulated output (from RF2) on most Sky boxes is about 70 dBμV, which equates to a medium strength signal, and as such it can often feed two points with a passive splitter, provided the cable runs aren`t too long. Note that if the Digi Link system is required this will not usually work through a splitter, even one with power pass, see below.
The “loop through” RF (from the aerial) is usually amplified slightly, about 4 dB, which is about the loss you`d get through a 2 way splitter. Thus if the output from the RF2 is fed into a 2 way splitter you`ll end up with what you had at the input to the Sky box, this obviously excludes any losses in the cable run(s).
The 9v (and, often, the IR return path signals) from the RF2 output on the Sky box will pass
through a spitter with power pass, but only from the output to the input, i.e. not in the direction required to actually use the splitter as a splitter !
If you need to feed more than one point and require Digi eyes to work use a Digilink amp.
If using a diplexer to add a Sky (or CCTV) signal to another UHF/VHF signal [e.g. from your TV aerial] a diplexer (of the type we sell) will pass the Digi link / IR return path signal and its accompanying 9V, but only on the low leg, not if the Sky output is connected to the high leg.
In addition, the power pass switch on the diplexer must be set to “on”.
So long as the low frequency leg is used (and the power pass switch is on), the 9V from the Sky box will also pass through and work this remote powered Digilink amp.
FM and DAB signals as well as TV can also be looped through the Sky digibox, as they can through Digilink amps.