power levels are not perfect
the technician said my power levels are not perfect but it will do. he put a 3db attentuator on
gaming feels sluggish, if i restart the hub it feels more responsive but after 24 hours it feels sluggish again.
Forum Discussion
The power levels only need to be within acceptable norms to deliver a reliable service.
The preferred range for Downstream power levels are -7 to +7 with +10 dBmV as the absolute max, some of the power levels exceed the maximum. Replacing the 3dB attenuator with a 10dB attenuator should bring the Downsteam into the preferred power range.
We are an RFoG installation and we have had a 10dB attenuator since day one.can you link me to the correct attenuator i need to purchase please?
RFOG will usually need an attenuator because the signal power source is at the house and it is supposed to put out 15dBmv.
In the OP’s case, the downstream SNR whilst within specs, isn’t the best and a high downstream power will amplify the noise. Hence the poor experience. Client62’s advice is sound and you get those attenuators in eBay if the VM bods won’t send you a tech.
so which forward path dB attenuator I need to purchase? 10db? 12db? 15db?
Sephiroth wrote:RFOG will usually need an attenuator because the signal power source is at the house and it is supposed to put out 15dBmv.
In the OP’s case, the downstream SNR whilst within specs, isn’t the best and a high downstream power will amplify the noise. Hence the poor experience. Client62’s advice is sound and you get those attenuators in eBay if the VM bods won’t send you a tech.
I've been studying the RFOG subject and I think I may have got my earlier post wrong. Have a look at this: chrome-extension://efaidnbmnnnibpcajpcglclefindmkaj/https://www.antronix.com/pdf/DS-1214-FF-A02_R-ONU.pdf
The key information is that the ONU outputs 17dBmv @ 860MHz when converting from fibre into the downstream. The return path (upstream) is put out at a nominal 33dBmv. So, nothing needs attenuation if the ONU used by VM operates to similar parameters.
Anyone seriously disagree with that?
Looking at your screenshots, the power levels are fine. The downstream SNR is a bit low. Also the upstream transmit levels are way lower than ideal.
My recommendation would be to definitely increase the 3db to a 10db attenuator. This will lower the DS levels, and the CMTS will instruct the modem to increase the upstream to around +38dBmV.
Sorry to argue. The upstream levels are fine. Your hub is just a few feet away from the media convertor, the low power is all it needs for the CMTS to read the upstream and in any case that is the commanded value.
If the OP is rebooting the Hub, I would question the large numbers of PostRS errors, as these will not be cumulative? Maybe some noise ingress as well as the power levels being a bit high?
We have a 10dB Wideband Attenuator it was fitted by VM during the RFoG install in 2017.
could you show me what it looks like, or link me to one on the internet?
This 6 dB attenuator is identical in appearance the technetix 10dB Wideband Attenuator on our line :
Whilst some may argue that the upstream levels are fine, it does depend what the HFC architecture is like between the CMTS and the RFOD Inverted Node. I personally re-aligned a service area near Newbury a couple of years back because the amplifiers were wrongly configured. This caused less than optimum levels in both directions & hence the amps were effectively degrading to noise performance by around 8-12db.
The modems used by VM all have similar sweet-spot for best performance. Downstream spec is indeed -7db to +7db, but they work best with downstream signal between 0db to 10db across the entire frewuency band. Max to Min difference should be << 3db, although it's common to see more than this.
Upstream depends on the SNR at the CMTS. Sweet spot for the transmit on the modem is 40-44dBmV, but between 38-52dBmV is probably ok. Most CMTS have around +15dBmV as the target receive with SNR >>38db. The only way to reliably achieve this is with decent transmit power from the modem.
Consequently using 6dB attenuator at the modem, will push the DS down to around 3-4dBmV, and the US will rise and improve the SNR at the CMTS.
OP. Make sure you use a wideband attenuator (not a forward path atten).
i am struggling to find a wideband attenuator 10dB.
Could you link me to ebay or anywhere on the internet please
I did purchase this one on amazon: https://www.amazon.co.uk/dp/B001C6K2FY?psc=1&ref=ppx_yo2ov_dt_b_product_details
but it sounds like its the wrong item.
Forcing the modem to transmit higher: You need to look at where you place the attenuator and where the (increased) noise floor is coming from. Between the home and the tap is usually what matters, so at the tap is where the attenuation makes most sense.
If you put the attenuator next to the modem, it has little/no impact on received SNR, because the signal is back down to the previous level right there.
In any event, it has no impact on the signal that hits the amplifier/node/R-ONU (RFoG).
