Signal Level and Ingress Guide

[weesteev]

Hi Guys

Here is the first in what will be a few helpful posts which should answer a lot of questions that pop up on this forum time and time again. The main reason for collating this information is to ensure that people aren't inadvertently creating issues on the VM network through Ingress (noise) which can impact their connection (and potentially everyone else on the same node!).

Please note - This information is provided from a personal point of view and is not an indictment of service from Virgin Media. Your first port of call for any signal/connection issues should be Virgin Media technical support.

Virgin Media Support Forum - https://community.virginmedia.com
0845 454 1111 or 150 from your Virgin Phone line.

Ingress

Ingress is the leakage of RF signal into the Virgin Media network from the customers premise/street cabinet. This causes a variety of issues from individual speed and connection issues for the customer impacted, to an entire node of customers being impacted (up to 500 customers) depending on the severity of the ingress.

The primary causes of Ingress from the customers property are...

• Unnecessary / un-terminated splitters
• Loose connectors
• Poorly fitted connectors
• Damaged cabling
• Unnecessary / unused / disconnected cabling
• Customer installed cabling & connections
• Faulty CPE device

Many of these issues can be resolved by engineer callout but again the majority of issues are caused by either damage to cabling within the property or improperly installed cabling... usually by the customer themselves.

I will never suggest that customers carry out their own connections/extensions at home but its hard to prevent this happening. Using the best quality materials, compression coaxial fittings and making sure that connectors are tightened properly is the best advice in the short term. Don't leave splitter ports or drop cables connected and un-terminated, this can cause a huge problem with noise on the local network and may inadvertently affect your connection.

In all circumstances where you require a connection moved or extended, please speak with Virgin Media in the first instance for advice and to arrange a Virgin Media engineer to carry out works.

Isolators

Isolators are used to block low frequencies associated with AC and DCmains power but allow the higher frequencies of the CATV network to pass.Isolators also protect CPE (customer premised equipment) from surges from the network and protects theVM network from power surges from the customers home.

Isolators perform to standards of EN-60728-11 – To withstanda continuous DC test voltage of 2120v for a period not less than 1min andmaintain an insulation resistance of 3MΩ.

In the UK, the use of fully isolated system outlets forevery piece of CPE is obligatory under the terms of the cable operating licence(as defined as EN-60728-11). Isolators must be fitted a wall entry point aswell as any additional room in the property not covered by the cable ingresspoint and the primary isolator. These are fitted only by Virgin Media engineers.

Please note - There will be a large number of customers that don't have conforming isolator installs due to legacy install issues and the varying install methods of cable companies in the past. This is something that will be rectified over time with service and install visits are undertaken, general maintenance is carried out at the same time. It is very unlikely your property will not have an isolator at the primary ingress point (either in an external ETB or internal wall mounted isolator housing),

Signal Levels

These signal levels are provided for information only, they can be used to quickly identify if there is a signal fault on your line (line stats are found on each devices administration pages). The Signal levels listed are the ideal frequencies expected at the customer equipment, there are varying levels at the ETB and ONU which will specify the line capabilities but these cannot be measured by the customer so will not be listed here.

Downstream Signal Levels @ CPE
QAM64 – Min -11dB, Max +5dB
QAM256 – Min -6dB, Max +10dB
Upstream Signal Levels @ CPE (64QAM, 4 bonded upstream @6.4Mhz)
FTTH – Min 27dB, Max 51dB
HFC – Min 33dB, Max 51dB

Signal Slope and Conditioning

Where the signal is either too high or too low, the line can be conditioned by either a simulator (reduce signal) or equaliser (increase signal) to bring the line quality back within specification. The options to use these are limited in 2018 as current CPE has better capabilities to handle a variety of signal ranges, but the following highlights when conditioning is required by a Virgin Media engineer...

Slope (CPE) -8 TO +8db

+9db use a 4db simulator reducing to +5db
>+9db – Network or install issue - Virgin Media networks input required.
-9db or -10db use a 2db wideband equaliser
-11db or -12db use a 4db wideband equaliser
<-12db – Network or install issue - Virgin Media networks input required.

These figures are very standard within the cable industry around the world on systems running up to 1200Mhz using DOCSIS 3.0. The migration to DOCSIS 3.1 in the long term will provide an option for wider frequency ranges so these figures will be reviewed as the network evolves.

Signal conditioning is only to be used when the drop cable is not faulty or damaged (no gel splices or barrel connectors in use).

Line Length

There is no standard line length specified by Virgin Media, the actual distance achievable will vary depending on the local network build and available tap ports in the cabinet/slot box. Not every tap port is the same with a range of signals catered for in the cabinet. The highest signals should be reserved for the longest drop cables where more power will be required over a longer cable length.

Generally, Virgin Media work to 100m drop cable lengths on average (either from slot box or cabinet). Cable lengths up to 100m will be RG6 whereas depending on port capacity RG11 may be used up to 150/200m at a push.

HDU - Home Distribution Unit

The HDU is a mains powered (DC) in home amplifier which helps reduce the loss generated by splitters and excessive cable runs within the customers home. The HDU will not boost the signal to the home but allows the received signal to be amplified around the in home wiring more effectively. If the customers home has 3 or more devices, long internal cable runs and has an incoming signal which is close to either the highest or lowest specification, then an HDU will be used to boost the signal within the home. These are fitted by a Virgin Media engineer and will only be fitted after signal tests within the property.

...

Hopefully this has been helpful, if anyone has any comments or questions please drop me a line.

[SnoopZ]

This is a great post, can we make it a sticky?

[weesteev]

Thanks Snoopz, have a few more guides in the pipepline. Also have some images to add to this one as well which should add a bit more value.

[weesteev]

Mods, any chance of a sticky on this one before I issue my next guide?

Stuck!

[SnoopZ]

If someone has 4x 16QAM upstreams are the recommended levels the same as 64QAM in the first post?

[vm_tech]

You can go a little higher with 16QAM, but for uniformity and future plans 51 is the defined specification.