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Aerial confusion

FrankieM

Standard Member
I have just moved into a house and found that no terrestial aerial sockets are working indoors. Looking at the existing set up there are 2 seperate aerials on the same mast which is attached to the side of the house. They are both pointing in the same direction. They have some sort of Labgear distributor equipment attached at the bottom.
Each aerial mast has its' own lead and they both go into the Labgear equipment. Inside it is marked up as Model CM7272
Can anyone help me understand this setup and would it be possible for me to "fix" it so everything is working. I have never seen an aerial set up with 2 seperate aerials being used.
Based on the bit of knowledge gained in these forums, do I need a diplexer to join the 2 aerials and then go through some sort of distribution system inside the house ?
Thanks for any help offered
 

Gavtech

Administrator
The CM7272 is a masthead amp that requires a 12V supply for it's operation.

That would normally be fed in [ via the coax] from some additional internal pass-thro power supply unit or an additional distribution amplifier.

It may also be supplied by equipment connected at the down end- if the equipment has the capability... but I think you will need to check what happens to the internal wiring first to find out if there are any more boxes.

More info on the CM7272 here.
 

FrankieM

Standard Member
Thanks GavTech
Can you do me qa favour please and translate "......from some additional internal pass-thro power supply unit or an additional distribution amplifier......" into simple speak.
I am not a technocrat by any stretch of the imagination, just someone who is trying to understand someone else's strange set up
 

MarkE19

Moderator
The passthrough power supply is This unit. You plug the unit into the mains and the coax cable from STB/TV in one RF conmnection and the feed from the amp to the other. The power is fed up the coax to the amp from close to the TV so no power supply is required at the actual amp in the loft/on roof.
Some PVR's etc can also supply the power via the coax so no additional PSU is required.

Mark.
 

FrankieM

Standard Member
OK chaps - phase 2 now underway.
Thanks to your help I now know where to buy the PSU but I think I now need to know what sort of cable to buy.
I need to add a TV in a loft bedroom which will act as the power supply for the system and this will require a new length of cable.
Do I use standard brown cable (which I have) or like many things nowadays is this a banned article.
Reading the forums some people suggest that it is unsuitable for digital.
If I have to buy a reel can you tell me the part number I will need and I will order from the same shop as the PSU
Cheers
 

Gavtech

Administrator
OK chaps - phase 2 now underway.
Thanks to your help I now know where to buy the PSU but I think I now need to know what sort of cable to buy.
I need to add a TV in a loft bedroom which will act as the power supply for the system and this will require a new length of cable.
Do I use standard brown cable (which I have) or like many things nowadays is this a banned article.
Reading the forums some people suggest that it is unsuitable for digital.
If I have to buy a reel can you tell me the part number I will need and I will order from the same shop as the PSU
Cheers

There are millions of installations using ordinary UHF coax that work completely satisfactorily for UHF digital applications.
Only in extremely challenging situations is it necessary to use better.

However, I'm puzzled regarding what exactly is planned - because if the CM7272 is a two outlet masthead amp... then it will be a three hole device presumably: One input , two outputs... but currently two holes are already being used for the two aerials... [I daren't imagine how these are wired. I presume they are just in parallel. Using two aerials to work together is often very tricky.] ... so you only have one outlet hole available.

If so, you may have to think about further distribution amplification if you are planning more than one outlet in the house... and if so, then the amp can supply the masthead power and the power supply unit is unnecessary.

As this installation, and what it is capable of, is a complete unknown at present [ are the aerials the correct group for now and the future?... for example ] it may be worth checking all the equipment you have, to see if any are capable of sending the 12V @ 25mA required by the masthead amp so you could perhaps test to see what you can receive and how well... before making further and perhaps mistaken investment.
 

FrankieM

Standard Member
GavTech - you must have been reading my mind. I was about to put electronic pen to paper when I saw your reply.
I was going to ask does anyone know why there are 2 seperate aerials.
I don't think the people who installed this knew exactly what they were doing because there are 2 aerial sockets inside the house but neither work.
I would like to get these working by the simplest (and cheapest) method.
I don't think there is anything wrong with the aerials, its just the cables that are coming out of them.
If I continue to use the CM7272 does this accept the 2 incoming seperate aerial leads - I assume not
 

Chris Muriel

Distinguished Member
The current installation just doesn't make sense.
The CM7272 should have 1 input (from a single aerial) and 2 outputs (to 2 separate wallplates or flying coax leads).
The 2 aerials could have been originally intended to be used stacked or bayed, I suppose - i.e. working together either side by side or 1 above the other. However, when stacking or baying the distance between the 2 aerials is also critical and they then require an appropriate passive combiner unit which has a single output to be fed to a unit like the CM7272 (at its input).
Are both aerials identical ? It is also possible to combine 2 different aerials each optimised for different UHF channel groupings with a (slightly different type of) combiner.

Just my thoughts on this puzzle....

Chris Muriel, in Boston, Mass this week but normally....
 

grahamlthompson

In memoriam
There are millions of installations using ordinary UHF coax that work completely satisfactorily for UHF digital applications.
Only in extremely challenging situations is it necessary to use better.

However, I'm puzzled regarding what exactly is planned - because if the CM7272 is a two outlet masthead amp... then it will be a three hole device presumably: One input , two outputs... but currently two holes are already being used for the two aerials... [I daren't imagine how these are wired. I presume they are just in parallel. Using two aerials to work together is often very tricky.] ... so you only have one outlet hole available.

If so, you may have to think about further distribution amplification if you are planning more than one outlet in the house... and if so, then the amp can supply the masthead power and the power supply unit is unnecessary.

As this installation, and what it is capable of, is a complete unknown at present [ are the aerials the correct group for now and the future?... for example ] it may be worth checking all the equipment you have, to see if any are capable of sending the 12V @ 25mA required by the masthead amp so you could perhaps test to see what you can receive and how well... before making further and perhaps mistaken investment.

This sounds to me like a diplexer rather than a straight amplifier. Read the section about diplexers here

Television/FM/DAB Aerial Amplifiers, Splitters & Diplexers
 

Gavtech

Administrator
This sounds to me like a diplexer rather than a straight amplifier.

I'd expect something of that nature... but going by the units model number given by the OP, it is specified simply as a a 2 outlet mast amp. :confused:
 

Gavtech

Administrator
The current installation just doesn't make sense.
The CM7272 should have 1 input (from a single aerial) and 2 outputs (to 2 separate wallplates or flying coax leads).
The 2 aerials could have been originally intended to be used stacked or bayed, I suppose - i.e. working together either side by side or 1 above the other. However, when stacking or baying the distance between the 2 aerials is also critical and they then require an appropriate passive combiner unit which has a single output to be fed to a unit like the CM7272 (at its input).
Are both aerials identical ? It is also possible to combine 2 different aerials each optimised for different UHF channel groupings with a (slightly different type of) combiner.

Just my thoughts on this puzzle....

Chris Muriel, in Boston, Mass this week but normally....

I agree... It's not right.

It is problematic not knowing whether this original installation has been done professionally [ and may have some additional provision inside the box for using two aerials ] or whether a second aerial has simply been bolted on by, perhaps the previous house owner in a misguided attempt to 'double the signal' ... or even perhaps by a cowboy flogging gear to a householder.

It's one of the reasons I was suggesting some attempt at a trial run, with a power supply from a piece of equipment ... in it's current condition to see if it has any performance at all.

That there are two aerials suggests that reception is going to be problematic in this location.

Frankie M - Do you know the transmitter these aerials will be receiving from? Are the elements horizontal or vertical? ... and is it possible to see how the aerials are internally wired in the masthead box?
 

FrankieM

Standard Member
Ok chaps here we go - when I first checked the aerials, only 1 was actualy connected inside the CM7272 - the second aerial lead was loose and hanging by the side.
The set up itself looks a bit amateur as the labgear unit was taped to the mast head by black gaffer tape and the mast unit is screwed into the wooden fascia.
Both aerials point in the same direction, are horizontal but one has more elements than the other.
I cannot tell which lead comes from which aerial but what I did was to connect each of them in turn to the CM7272 input and then checked a TV connecetd to one of the sockets inside the house.
One of the aerials gives me some channels on DVB with a certain strength and the other aerial gives a different selection of aerials with a stronger signal.
Is this what you mean by them both doing different jobs ?
At this stage I have not connected the CM7272 to any power unit, it is only being fed from the TV itself.
What is my next option - is it to add a diplexer so I can use both aerials at the same time ? and then connect the CM7272 to a power supply ?
 

Gavtech

Administrator
Ok chaps here we go - when I first checked the aerials, only 1 was actualy connected inside the CM7272 - the second aerial lead was loose and hanging by the side.
The set up itself looks a bit amateur as the labgear unit was taped to the mast head by black gaffer tape and the mast unit is screwed into the wooden fascia.
Both aerials point in the same direction, are horizontal but one has more elements than the other.
I cannot tell which lead comes from which aerial but what I did was to connect each of them in turn to the CM7272 input and then checked a TV connecetd to one of the sockets inside the house.
One of the aerials gives me some channels on DVB with a certain strength and the other aerial gives a different selection of aerials with a stronger signal.
Is this what you mean by them both doing different jobs ?
At this stage I have not connected the CM7272 to any power unit, it is only being fed from the TV itself.
What is my next option - is it to add a diplexer so I can use both aerials at the same time ? and then connect the CM7272 to a power supply ?

Yes you need a power supply... A power supply can be a separate unit or can be within an active splitter or distribution amplifier also so the only problem in that regard is if you get a standalone power supply unit and then subsequently require an amplifier, you will have wasted money on the PSU.

If two outlets is all you are going to need, then the existing Mast amp can provide that and so you only need a PSU. If you think at any time your configuration will require more outlets then you may as well get an active splitter now which can provide the required 12V power.

It's encouraging that you can get anything at all without a power supply to the mast unit.

It's also a relief that there is only one aerial connected inside the unit.

The aerials may be different groupings so it is difficult to know what is best done in that regard... especially given all the changes occurring in the transmission infrastructure. It may be you will be able to get the main muxes but not all. It is geographically dependent.

If you wish to send me the postcode by PM I will look into what can be expected to be received at the location.
 

FrankieM

Standard Member
If the 2 aerials are doing different jobs, should I buy a diplexer which combines them so they become the single input and then a power supply for the CM7272. This means I can then have 2 outputs and if necessary split into one of them inside the house if necessary ?
 
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Gavtech

Administrator
Post Code is IP21 4DR
If the 2 aerials are doing different jobs, should I buy a diplexer which combines them so they become the single input and then a power supply for the CM7272. This means I can then have 2 outputs and if necessary split into one of them inside the house if necessary ?

I've sent you a link via PM.

As you will see , you should receive from Tacolneston transmitter and only one aerial is required [a Group CD aerial].

This should give you all the current muxes provided it is sensitive enough.

Using two aerials is to be avoided if at all possible.

The only implication is that after June 2011, after the DSO [ digital switch over ] the muxes will be reorganised and increased and two of the muxes will then fall outside your aerials receptivity... [albeit they will be mostly garbage muxes]

If you really want them you could change to a wideband aerial... Indeed it is possible that one of the aerials fitted on the mast is already a wideband...but you will get better receptivity from a grouped aerial.

So - No you don't need two aerials and I cant see that you ever will.


Given your last question, if you are considering splitting the signal further then I suggest you get an active splitter a.k.a. a distribution amplifier, rather than a power supply.

The distribution amp will [ or can ] have provision to provide the 12V required by the mast amp. [ ensure it is capable of delivering 12V at 25mA]
 

radioredcat

Active Member
Those amps pass a signal with no power obviously not amplified so if you put power to the amp the signal will improve.

As for the two aerials only one is being used so just ignore the other one and try it.

andy
 

mike7

Distinguished Member
Yes you need a power supply... A power supply can be a separate unit or can be within an active splitter or distribution amplifier also so the only problem in that regard is if you get a standalone power supply unit and then subsequently require an amplifier, you will have wasted money on the PSU.

If two outlets is all you are going to need, then the existing Mast amp can provide that and so you only need a PSU. If you think at any time your configuration will require more outlets then you may as well get an active splitter now which can provide the required 12V power.

It's encouraging that you can get anything at all without a power supply to the mast unit.

It's also a relief that there is only one aerial connected inside the unit.

The aerials may be different groupings so it is difficult to know what is best done in that regard... especially given all the changes occurring in the transmission infrastructure. It may be you will be able to get the main muxes but not all. It is geographically dependent.

If you wish to send me the postcode by PM I will look into what can be expected to be received at the location.

I've sent you a link via PM.

As you will see , you should receive from Tacolneston transmitter and only one aerial is required [a Group CD aerial].

This should give you all the current muxes provided it is sensitive enough.

Using two aerials is to be avoided if at all possible.

The only implication is that after June 2011, after the DSO [ digital switch over ] the muxes will be reorganised and increased and two of the muxes will then fall outside your aerials receptivity... [albeit they will be mostly garbage muxes]

If you really want them you could change to a wideband aerial... Indeed it is possible that one of the aerials fitted on the mast is already a wideband...but you will get better receptivity from a grouped aerial.

So - No you don't need two aerials and I cant see that you ever will.


Given your last question, if you are considering splitting the signal further then I suggest you get an active splitter a.k.a. a distribution amplifier, rather than a power supply.

The distribution amp will [ or can ] have provision to provide the 12V required by the mast amp. [ ensure it is capable of delivering 12V at 25mA]

If Gavtech lives in central Norwich there is an area which is something of a 'black spot' and is served by a low power transmitter (has vertical polarisation). There are some people that have used a mix of signals from this and Tacolneston. Might be behind the problem. I'm assuming this transmitter will switch off in 2011.
 

FrankieM

Standard Member
Thanks to everyone - now to the details
I will leave the aerial as it is and only use 1.
I want to use the CM7272
So, can anyone recommend whar PSU I need and what active splitter I need (with part numbers). I can then order them from 1 place
 

Gavtech

Administrator
Thanks to everyone - now to the details
I will leave the aerial as it is and only use 1.
I want to use the CM7272
So, can anyone recommend whar PSU I need and what active splitter I need (with part numbers). I can then order them from 1 place

This, or similar, may be suitable.

It will provide power for the masthead amp, and has an option for four outputs for distribution elsewhere.
 
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FrankieM

Standard Member
Gavtech, I wonder if you can give me some more advice
I have been offered a PHILEX SLx4 4 WAYAERIAL AMPLIFIER (for TV, VCR & Satellite or FM receivers) to do the job I require.
It has an auto line powering on the UHF socket
Spec is as follows:-
Gain: 10.5dB
Noise Figure: < 4dB
Line Power: 12v
Isolation: >22dB
Rated power: <5W
Impedance: 75 Ohms
Frequency: VHF 47 - 230 MHz
UFH 470 - 863 MHz
FM 88 - 108 MHz
Is this OK for the job I want do you think - I wouldn't like to open the plastic cover and then discover it was not what was needed.
Thanks
 

Gavtech

Administrator
Gavtech, I wonder if you can give me some more advice
I have been offered a PHILEX SLx4 4 WAYAERIAL AMPLIFIER (for TV, VCR & Satellite or FM receivers) to do the job I require.
It has an auto line powering on the UHF socket
Spec is as follows:-
Gain: 10.5dB
Noise Figure: < 4dB
Line Power: 12v
Isolation: >22dB
Rated power: <5W
Impedance: 75 Ohms
Frequency: VHF 47 - 230 MHz
UFH 470 - 863 MHz
FM 88 - 108 MHz
Is this OK for the job I want do you think - I wouldn't like to open the plastic cover and then discover it was not what was needed.
Thanks

I was concerned about the line power current capability because it is not specified above... so started to look around for specifications.

In doing so, I became additionally concerned that many specifications say there is 12V line power available on all outputs....which makes no sense as it is the 'input' that requires to send line power.

However, going to the 'horse's mouth' - Philex - I found more categorical specs. http://technical.philex.com/downloads/rf/SLx4.pdf ... which shows that the line current rating is adequate [ 25mA] and comes from the correct port.

Note that there is another version of this amp with a 'B' suffix which includes a bypass for skybox control signals - Not applicable in your case as I understand it... but for others - here's a link to info here.

So - Yes. All the other specs are OK. I believe that amp is suitable.
 

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