uhf amplification kills skynews/mtv/setanta

Synkro

hi,

We have Ntl cable (analog) coming into our house. The connection on the roof has 4 ports. (in & out & 2 for our house). When the signal is fed directly to the tv ie no splitting, we get ALL channels almost perfectly. However as soon as the cable is split or sent throught a distributing amplifier, the tv channels are very poor.

I have tried with different amplifiers and was almost about to give up until i experimented with an 8way dual uhf & vhf input amp. This amp has specific uhf and vhf inputs. when i connect to the vhf only input all tv channels are perfect expect skynews/mtv/cnbc. This is because these three channels are broadcast on uhf.

I then plugged into the uhf input and naturally enuff all vhf reception is blocked and only uhf is passed and amplified, BUT the 3 uhf stations are very poor and unwatchable.



To summarise...

#1
The direct NTL is perfect.

#2
The vhf part of the signal is perfect when amplified and split.

#3
Any attempt to amplify the Uhf band results in the 3 uhf channels being lost.

This is my theory and any other opinions would be really appreciated.

Could it be possible that there is some noise/interference on the uhf band that normally doesnt cause a problem when the ntl cable is fed directly to the tv (ie no splitting) BUT when i attempt to send the signal thru my 8way amp whatever co-channel noise that is on the cable is amplified to such an extent that it wipes out the 3 uhf channels i want?

Would this be a solution...

install 3 bandpass filters/tuned filters in parrallel before the amp in order to ONLY pass the 3 uhf tv channels, and then the amp will have a clean/noise free uhf source to amplify?

Many thanks for any feedback in advance.

Adrian

Frequencies for Dublin Cable


The Discovery Channel 48 MHz
Channel 4 56 MHz
E4 64 MHz
Network 2 176 MHz
TV3 184 MHz
RTE 1 192 MHz
UTV 200 MHz
TG4 208 MHz
BBC 1 216 MHz
BBC 2 224 MHz
Sky One 232 MHz

*Nickelodeon/Paramount 264 MHz
*MTV 256 MHz
*Sky News 280 MHz
*CNBC 408 MHz
*Setanta Sports 248 MHz

The Discovery Channel 575 MHz
Channel 4 543 MHz

bazzer

The only way to be sure when dealing with amplifiers is to ensure that they are specified to cover the entire VHF and UHF ranges from 40MHz to 860MHz with NO interruptions in between. This means VHF bands 1, 2, 3, Superband, Hyperband and UHF Channels 21-69. The problem with many amplifiers imported from the UK is that they cover only Bands 1 and 3 on VHF, which is totally useless for Irish cable installations. In addition, they're mostly the non-screened type, which is just asking for trouble.

Another thing to consider is the gain properties of the amplifier. Variable attenuators will help, but if the gain is too high, you will create harmonics of the channels all beating against each other and causing interference, such as that you are seeing on the NTL channels on UHF.

Bottom line: get rid of your existing amp and start again. Steer clear of the likes advertised in Argos, go to a specialist TV equipment stockist.

To correct you, Sky News, MTV and CNBC are not on UHF, Sky News and MTV are on the VHF Superband and CNBC on VHF Hyperband.

watty

45 .. 70 is band I (approx)
170 .. 275 is Band III VHF

275 to 460 is hyperband (cable only for TV)

470 to 890 is UHF.

Try a VHF/UHF diplexer to split the cable signal and feed its two outputs into your amp.

The tax man

Too many crap amps being sold that stop around the 230mhz range.
See them every week.
As Bazzer said get rid of and start with a decent amp WITH gain control.

Synkro

Thanks Bazzer & Watty!

This is the amplifier I am using.
http://www.maplin.co.uk/Module.aspx?ModuleNo=29416&criteria=tv%20amplifier&doy=2m1
I purchased it from Maplin so no doubt it is UK destined.

I read the datasheet and as you said it stops just short of the channels i want to amplify.

VHF: 45 - 230 mhz
UHF: 470 - 860 mhz



Here is the datasheet.

http://www.maplin.co.uk/Media/product_pdfs/KR20.pdf


Could you recommend something suitable and or somewhere to buy it?

Many thanks.

Adrian

Synkro

Was onto electroplus thismorning. their amps only seem to go as far as 400mhz which unfortunatly stops short of CNBC on 408mhz. Its rated at 20db with variable gain and has a single input & output. I plan to feed the ntl cable thu the 3 modulators first then into the amp and then through an 8way splitter (40-2050mhz) and finally at the unused tv points I'll plug in 75ohm terminators. Hopefully that will work!

thanks for help

Synkro

I have just realised that the amlifier I mentioned in my last post will not pass the 3 uhf signals from the modulators (ch 21 - 69, 471.25-855.25mhz).

I have rung around and apparently wideband amplifiers are very hard to get hold of.

Im looking for a fully screened amp with variable gain and a freq range of 40-800mhz.

Does anybody know of any dublin based suppliers?



Thanks

adrian

watty

408MHz will work on a "400MHz" amp.

The modulators are often high level and thus it doesn't matter if they are attenuated a little. That Electroplus amp might work.

Use a splitter to combine the Cable TV and the modulators as the "pass through" may not be great at VHF or Hyperband.

It might be a good plan.

Alternatively combine the "modulators" after the VHF/Hyperband amp. If the 8 way passive splitter attenutes the modulators too much use a variable gain UHF amp on the output of them to feed the 2 way passive splitter used to combine the Hyperband electroplus amp and the UHF amp.

Synkro

Hi watty,

Picked up a TRIAX 20db screened amp, with freq resp. 47 - 850mhz. Also has variable gain. It only has a single f-connector output so I have an 8way splitter and some 75ohm terminators for the unused tv points. Hope to get it installed tomorrow evening and will post back with results.


btw, I rang through the list of suppliers on your wiki page, and Zintek were the only ones to stock the wideband amp.


tnx for help.

adrian

Sparky

jesus its a pitty i didnt see this page sooner.
I was in electroplus thismorning also, (John in sales) gave me a televes MATV amp, and i used my incoming feed and splitted it into the UHF VHF connectors, now the wierd thing is in the output, if i have one tv on its picture is perfect but if i have 2 tv with a 5-1000mhz splitter the picture goes crap, so as a matter of interest i connected the other tv into the -30db test outlet which gave a clearer picture than the normal output and with the inclusion of CNBC, which i was informed would not be amplified.

So rang around and the best amp ive been told to get is a labgear 8way amp, i know the ref code, just dont have it at the moment.

All this is a replacement for the old Wosley amp.

Ive seen the Triax amp, its black afaik with a bright blue led, am i right?

Oh and can i get some report on how the triax amp works as ive already spent €147 on a televes amp thats doing no good, cheers