On 21 Sep 2006 17:04:32 -0700, "Mark" <makolber@yahoo.com> wrote:

>> > You can sometimes get a bit better ISI with a bit of equalisation as the
>> > channel filter often puts a bit of  slope at the band edges and this isn't
>> > always equalised in the uplink.
>> >
>> > Best of Luck - Mike
>> >
>> >
>>
>> By the way IF you do need an equalizer it probably doesn't have to be very
>> long (4-5 symbols) so the answer may be better safe than sorry since it
>> won't cost you much.
>>
>> -Clark
>
>There are many things in the system that could put some slope in the
>system, for example  the transmission lines feeding the antennas may
>have some mis-match and can cause ripple in the passband.  Adaptive EQ
>will improve that.  You may not NEED to have adaptive EQ to close the
>link,   but adaptive EQ in the receiver will help to keep the
>implementation losses in the overall system at a minimum.
>
>Mark

Yeah, that's generally right by my understanding, i.e., the only
reason to use an EQ in a satellite link is to correct for tilt or
other non-flat signal pass behavior in the transponder.  This usually
only comes into play when trying to use higher-order modulations like
16-QAM or higher.

There's no multipath to speak of in satellite systems as there are no
significant reflectors along the signal path and the antennas are
highly directive.

Eric Jacobsen
Minister of Algorithms, Intel Corp.
My opinions may not be Intel's opinions.
http://www.ericjacobsen.org

> > >>
> > You can sometimes get a bit better ISI with a bit of equalisation as the
> > channel filter often puts a bit of  slope at the band edges and this isn't
> > always equalised in the uplink.
> >
> > Best of Luck - Mike
> >
> >
>
> By the way IF you do need an equalizer it probably doesn't have to be very
> long (4-5 symbols) so the answer may be better safe than sorry since it
> won't cost you much.
>
> -Clark

There are many things in the system that could put some slope in the
system, for example  the transmission lines feeding the antennas may
have some mis-match and can cause ripple in the passband.  Adaptive EQ
will improve that.  You may not NEED to have adaptive EQ to close the
link,   but adaptive EQ in the receiver will help to keep the
implementation losses in the overall system at a minimum.

Mark

"Mike Yarwood" <mpyarwood@btopenworld.com> wrote in message
news:Fe6dnZRMZrFeU4_YRVnytQ@bt.com...
>
> "Anonymous" <someone@microsoft.com> wrote in message
> news:owyQg.32477$Md4.26578@tornado.southeast.rr.com...
> >
> > "tmoshe" <moshe.twitto@horizonsemi.com> wrote in message
> > news:Q6-dnQlzfN_tL4_YnZ2dnUVZ_vudnZ2d@giganews.com...
> >> Thanks guys,
> >>
> >> I would like to reffer to some of your comments.
> >>
> >> Howard: Of course I use matched filter. But with fixed coefficients, I
> >> forgot to note that.
> >>
> >> Clark: I'm running agc over each channel (about 40Mhz), after I got it
> >> from the tuner. Is that enough or there is possibility that there will
be
> >> varations in the gain INSIDE a channel??? If so I think that equalizer
is
> >> obligatory.
> >>
> >
> > PSK is fairly immune to small gain changes. If your matched filter
undoes
> > the ISI then you can probably live without the EQ. In my product I don't
> > know the shaping ahead of time so I need an equalizer to determine the
> > matched filter for me.
> >
> >> Vladimir: to my opinion, due to the directionality of the sat-antenna,
> >> the
> >> multipath are very week (less than -20dBc in most cases).
> >>
> You can sometimes get a bit better ISI with a bit of equalisation as the
> channel filter often puts a bit of  slope at the band edges and this isn't
> always equalised in the uplink.
>
> Best of Luck - Mike
>
>

By the way IF you do need an equalizer it probably doesn't have to be very
long (4-5 symbols) so the answer may be better safe than sorry since it
won't cost you much.

-Clark

"Anonymous" <someone@microsoft.com> wrote in message 
news:owyQg.32477$Md4.26578@tornado.southeast.rr.com...
>
> "tmoshe" <moshe.twitto@horizonsemi.com> wrote in message
> news:Q6-dnQlzfN_tL4_YnZ2dnUVZ_vudnZ2d@giganews.com...
>> Thanks guys,
>>
>> I would like to reffer to some of your comments.
>>
>> Howard: Of course I use matched filter. But with fixed coefficients, I
>> forgot to note that.
>>
>> Clark: I'm running agc over each channel (about 40Mhz), after I got it
>> from the tuner. Is that enough or there is possibility that there will be
>> varations in the gain INSIDE a channel??? If so I think that equalizer is
>> obligatory.
>>
>
> PSK is fairly immune to small gain changes. If your matched filter undoes
> the ISI then you can probably live without the EQ. In my product I don't
> know the shaping ahead of time so I need an equalizer to determine the
> matched filter for me.
>
>> Vladimir: to my opinion, due to the directionality of the sat-antenna, 
>> the
>> multipath are very week (less than -20dBc in most cases).
>>
You can sometimes get a bit better ISI with a bit of equalisation as the 
channel filter often puts a bit of  slope at the band edges and this isn't 
always equalised in the uplink.

Best of Luck - Mike

"tmoshe" <moshe.twitto@horizonsemi.com> wrote in message
news:Q6-dnQlzfN_tL4_YnZ2dnUVZ_vudnZ2d@giganews.com...
> Thanks guys,
>
> I would like to reffer to some of your comments.
>
> Howard: Of course I use matched filter. But with fixed coefficients, I
> forgot to note that.
>
> Clark: I'm running agc over each channel (about 40Mhz), after I got it
> from the tuner. Is that enough or there is possibility that there will be
> varations in the gain INSIDE a channel??? If so I think that equalizer is
> obligatory.
>

PSK is fairly immune to small gain changes. If your matched filter undoes
the ISI then you can probably live without the EQ. In my product I don't
know the shaping ahead of time so I need an equalizer to determine the
matched filter for me.

> Vladimir: to my opinion, due to the directionality of the sat-antenna, the
> multipath are very week (less than -20dBc in most cases).
>
>

Thanks guys,

I would like to reffer to some of your comments.

Howard: Of course I use matched filter. But with fixed coefficients, I
forgot to note that.

Clark: I'm running agc over each channel (about 40Mhz), after I got it
from the tuner. Is that enough or there is possibility that there will be
varations in the gain INSIDE a channel??? If so I think that equalizer is
obligatory.

Vladimir: to my opinion, due to the directionality of the sat-antenna, the
multipath are very week (less than -20dBc in most cases).

tmoshe wrote:

> Does signal from geostationaric satellite need to be equalized?
> I'm talking about static receivers, not mobile.

There could be a need for the equalization because of the multipath 
propagation.

Vladimir Vassilevsky

DSP and Mixed Signal Design Consultant

http://www.abvolt.com

"tmoshe" <moshe.twitto@horizonsemi.com> wrote in message
news:4tudneFujZKIo4_YnZ2dnUVZ_tCdnZ2d@giganews.com...
> Does signal from geostationaric satellite need to be equalized?
> I'm talking about static receivers, not mobile.
> Because as far as I understand this channel, except for non-linear
> distorion due to high-power amplifiers, which does not affect M-PSK
> modulations, there are no other distortions that require equalization.
> Please help me with this!!!
> Thanks,
> Moshe
>

Well you need some equalization just to undo the ISI caused by the symbol
shaping filter. Depending on the roll off factor it can be pretty distorted
even direct from a signal generator. However, I think you're right the delay
spread should be very minimal since there's really nothing to reflect off
of.

I would google: "delay spread" "satellite channel" and see what pops up.

-Clark

"tmoshe" <moshe.twitto@horizonsemi.com> wrote in message 
news:4tudneFujZKIo4_YnZ2dnUVZ_tCdnZ2d@giganews.com...
> Does signal from geostationaric satellite need to be equalized?
> I'm talking about static receivers, not mobile.
> Because as far as I understand this channel, except for non-linear
> distorion due to high-power amplifiers, which does not affect M-PSK
> modulations, there are no other distortions that require equalization.

If we are talking about a non-regenerative transponder channel that is 
sub-divided into smaller FDMA uplink sub-channels using the same HPA, then 
equalization across the entire transponder channel passband would be 
beneficial in order to ensure that one uplink does not use more HPA power at 
the expense other uplinks.

It is possible (indeed highly likely in practice) that one uplink will be 
stronger than another for many reasons such as off-pointed antennas or 
polarization mismatch.

Typically correction can be achieved by providing frequency specific AGCs 
across the transponder's passband using a dynamically calculated custom 
filter.

Cheers, Howard 

Hi Particlereddy,
Thanks!
Of course that there is fading but I think that it is very slow, so 
again, no equalizer is needed.

>hi tmoshe,
>              quite interesting question you asked. Regarding
>satellite, their antennas will be pin pointed towards receiver earth
>station antennas (powerfull directioned antennas).
>if it is perfectly so
>1. no question of multipath.
>
>2. regarding fading, definately it will be there..
>
>3, since you told it is static, no doppler effect.
>
>hope, there are many greats here in this group.they will come up with
>very good answers
>:)
>
>regards
>particlereddy
>
>
>tmoshe wrote:
>> Does signal from geostationaric satellite need to be equalized?
>> I'm talking about static receivers, not mobile.
>> Because as far as I understand this channel, except for non-linear
>> distorion due to high-power amplifiers, which does not affect M-PSK
>> modulations, there are no other distortions that require equalization.
>> Please help me with this!!!
>> Thanks,
>> Moshe
>
>