Aerial problem upgrading to a Sagem PVR

Discussion in 'Freeview & YouView' started by Phil_L, Jan 9, 2008.

  1. Phil_L

    Phil_L
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    I have been using a Philips Freeview box with an aerial located in the loft without any problems for several years and it gives a good picture on all the Freeview channels. I recently decided to upgrade to a Sagem PVR, but when I connected it up I found that the only watchable channel was BBC1 with most other channels giving picture problems which kept caused the Sagem box to switch itself off.

    The high street store where I purchased the Sagem, refuse to take the box back and refund my money as they say that the problem is solely due to my loft aerial which I need to upgrade to a roof top one.

    If my loft aerial is good enough for my current Philips box, then should it not also be adequate for the Sagem PVR or any other Freeview box?

    If "all boxes are not the same" and retailers refuse to take boxes back which are unsuitable, then how can I tell which Freeview boxes are likely to work with my aerial prior to purchase?

    However, as I really do not wish to upgrade my aerial at this time (and would not have bought the Sagem box if I had known I would need to), then am I now stuck with a PVR which is effectively useless to me?

    I would be grateful for any advice!

    Thanks
    Phil
     
  2. LV426

    LV426
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    The difference in signal level between "just good enough to be perfect" and "not good enough for stable reception" and "not enough for anything at all" is tiny. A miniscule difference in tuner sensitivity, with a marginal signal to start with, may well produce the effect you describe.

    Loft aerials are better than in-room aerials (generally) but are nowhere near as suitable as a proper outdoor installation. The building materials used for roofs are partly opaque to radio waves and can reduce your strength by 50% give or take.

    This is, it seems, wholly a matter for you to resolve. It's unrealistic to expect a digital receiver to receive with an inadequate signal; it's unrealistic to expect a loft aerial to produce an adequate signal (except in a minority of "lucky" locations) and it's unreasonable to expect a remedy from a retailer or manufacturer for a non-faulty piece of equipment.
     
  3. mrfreeview

    mrfreeview
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    Receiver Sensitivity is the reason why some STB work and others don't with a low level signal strength.

    The receiver sensitivity may be quoted by a manufactuer in their handbook. (Then again it may not!)The figure should be quoted in dBm. Some are as poor as, typically -78dBm. However this figure varies from manufactuer to manufactuer and some have produced STBs that will work down to as low as -90dBm

    You should also note that an extra 6dB of signal strength is required to decode a 64QAM MUX over that required for a 16QAM. So when a manufacturer quotes a sensitivity figure and then does not quote the QAM to which is refers you have to assume worst case.

    So what is the difference between -90dBm and -84dBm (6dB!)

    And a change of 3dB = half / twice power. So 6dB is 1/2 of 1/2 = 1/4 (or 4 times if going up in power not down)

    So for a decoder that specifies a minimum signal strength of -84dBm then 4 times more signal strength (signal power) is required by this decorder than the decorder specified at -90dBm.

    Hope my post makes sense and has been of use :)
     
  4. Phil_L

    Phil_L
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    Thank you both for your helpful and interesting responses.

    As I was not convinced that the Sagem box was entirely fault free, I tried it out at a friend's house (fitted with a new roof top aerial). My hunch proved correct - after 2 hours of use, the Sagem box failed completely and since then has refused to start up (suspected hard drive failure).

    I took it back to the store today, reported it "dead" and got a refund without any further hassle.

    So I guess that solves the problem for now!

    Phil.
     

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