Is a Stacked LNBF better than a Quad LNBF (1 Viewer)

Register Today to see less ads! It's Free!
Status
Please reply by conversation.

Cband55

Thread Starter
SatelliteGuys Pro
May 14, 2008
202
1
I just had a agrisous time with a installer that insisted that I had to change my quad LNBF for a Stacked one, he said if he was not able to install the Stacked LNBF he would not leave the IRD, i let him but as soon as he left I changed the stacked LNBF back to the quad LNBF.

In tech terms

My FTA did not work on the Stacked LNB but did on the quad

I would like to know if a stacked LNBF has any disadvantages
thanks
 
Last edited by a moderator:
Register Today to see less ads! It's Free!

Cband55

Thread Starter
SatelliteGuys Pro
May 14, 2008
202
1
Ku LNBF the Quad is in the backgorund,
 

Attachments

  • Imagen55 045.jpg
    Imagen55 045.jpg
    19.6 KB · Views: 189
  • Imagen55 043.jpg
    Imagen55 043.jpg
    49.5 KB · Views: 203
  • Imagen55 046.jpg
    Imagen55 046.jpg
    29.6 KB · Views: 206

USDownlink

SatelliteGuys Pro
Mar 19, 2008
352
16
Oregon
I am seeing an apples/oranges problem here. Stacked or not is only tangentially related to the number of independent outputs on a particular LNB.

Someone please correct me as I've no experience with one, but a stacked LNB eliminates voltage polarity switching in favor of one polarity being shifted up in L band frequency, above the other polarity. A multiple output LNB allows multiple receivers to attach to the same LNB and treat it as if it was the only receiver connected.

I guess a stacked LNB, assuming an independent power source and probably a fixed dish, could be split with high frequency splitters and work with multiple receivers. A rather atypical installation, but possible.

CBand55: My question is what kind of receiver was the installer leaving behind? You mention an FTA receiver, but I read your post as you wanting to use the LNB/dish on an existing FTA system.

Incidentally, even if an FTA box doesn't natively support a stacked LNB, it usually possible to fool it into tuning stacked frequencies.
 

Tron

SatelliteGuys Master
May 6, 2005
6,599
33
Metro New Orleans, LA
Disadvantages of stacked LNBFs are:

- One polarity will be stacked above the other, therefore the TP frequencies will be off on the polarity that is stacked. No big deal, simple math or a blind scan receiver will find them.

- Since stacked LNBFs stack frequencies above the commonly used L-Band frequencies, all components (cables, switches, ground blocks, amps if applicable) must be able to pass at least 2.1 ghz (preferably 2.2 or higher, depending on rolloff).

Other problems may be present, depending on what kind of system you are using. Most, if not all, FTA receivers should have no additional issues.
 

B.J.

SatelliteGuys Pro
Oct 15, 2008
2,029
1
Western Maine
Disadvantages of stacked LNBFs are:

- One polarity will be stacked above the other, therefore the TP frequencies will be off on the polarity that is stacked. No big deal, simple math or a blind scan receiver will find them.

- Since stacked LNBFs stack frequencies above the commonly used L-Band frequencies, all components (cables, switches, ground blocks, amps if applicable) must be able to pass at least 2.1 ghz (preferably 2.2 or higher, depending on rolloff).

Other problems may be present, depending on what kind of system you are using. Most, if not all, FTA receivers should have no additional issues.

The fall-off at higher freq would be the main reason that I'd never go for a stacked LNBF. With my ~250' coax run, I can see a drop in signal when I get to the upper end of the band. If I had to go up another 500 MHz, I don't think I'd have much signal left.

However another possible disadvantage is that by sending both polarities over the same band at once, unless the lnbf has a very sharp band-pass filter, you're going to get interferrence from circular DBS freqs in the upper band. Also, on sats where there are signals below 11700, you'll get interferrence from the lower band on the other polarity. It COULD be that they have a very good bandpass filter, but I doubt that it's possible for a consumer priced lnbf, and even the best bandpass filter would have interferrence on one or two transponders.

Anyway, no way would I ever consider using a stacked system.
 

pendragon

SatelliteGuys Pro
Oct 13, 2008
1,100
63
I use both stacked and non-stacked LNBs throughout my system. They both work fine, performance-wise. If I have a long cable to a stacked LNB, I employ an amplifier with some slope compensation. I see no difference in quality compared to a non-stacked LNB in that situation.

In terms of interference, I have also found no issues with stacked LNBs. One acid test is using a Superdish stacked FSS LNB at 111.1W for Shaw Direct. 111.1W is nowhere near the power of Dish Network's 110W, here. If there was insufficient filtering in the stacked LNB, 110W would cause a LOT of interference because the FSS LNB uses an inverted spectrum for the horizontal polarization (1650-2150 MHz). That means 110W's frequency spectrum maps directly into both the H & V polarizations of 111.1W.

The same sort of thing happens at 72W & 72.7W. I've tried similar quality stacked and non-stacked LNBs on toroids and 1.2m offsets for both of these orbital pairs. In my limited testing, the stacked LNBs always had at least the CNR as the non-stacked LNBs, and often better. The bandpass filtering is more than adequate on the stacked LNBs, and because the non-stacked LNBs might not have as much, it's possible they are more susceptible to saturation from the higher frequency, higher powered signals.
 

Tron

SatelliteGuys Master
May 6, 2005
6,599
33
Metro New Orleans, LA
I personally prefer stacked LNBs. While I don't have an extremely long cable run, I've never seen performance problems, and the advantages are considerable. Having both polarities always available is worth the extra trouble IMO. It is almost like having orthomode feeds.
 

classicsat

SatelliteGuys Pro
Nov 28, 2009
195
0
Ontario, Canada
I have a dual stacked Shaw Direct/Starchoice dish used for that service, and it works just fine. It only requires me to run two coaxes into the house, which is split there and sent to my 2x2 tone switches to feed my Shaw Direct receivers, which are soft programmed to tune Stacked LNBFs.
 

pendragon

SatelliteGuys Pro
Oct 13, 2008
1,100
63
In terms of interference, I have also found no issues with stacked LNBs. One acid test is using a Superdish stacked FSS LNB at 111.1W for Shaw Direct. 111.1W is nowhere near the power of Dish Network's 110W, here. If there was insufficient filtering in the stacked LNB, 110W would cause a LOT of interference because the FSS LNB uses an inverted spectrum for the horizontal polarization (1650-2150 MHz). That means 110W's frequency spectrum maps directly into both the H & V polarizations of 111.1W.

The same sort of thing happens at 72W & 72.7W. I've tried similar quality stacked and non-stacked LNBs on toroids and 1.2m offsets for both of these orbital pairs. In my limited testing, the stacked LNBs always had at least the CNR as the non-stacked LNBs, and often better. The bandpass filtering is more than adequate on the stacked LNBs, and because the non-stacked LNBs might not have as much, it's possible they are more susceptible to saturation from the higher frequency, higher powered signals.

I was messing around with dishes and got to thinking about this a bit more. I figured it might be interesting to take some spectrum analyzer shots comparing a bandstacked LNB to a normal North American Ku LNB. To be frank, I was a bit lazy and the results suffer a bit from comparing apples to oranges, but the difference is striking enough that the point is still valid.

The first shot is looking through a Dish Network Superdish FSS bandstacked LNB with a DN DP feed on a Wave Frontier T90 toroid at about 15 degrees off-axis. The feed is adjusted for Shaw Direct's 111.1W bird and I'm picking up the horizontal polarization via a DishPro legacy adapter to invert the spectrum and place it at a 950-1450 MHz IF. The center frequency in the shot is 12185 MHz, which is the highest frequency transponder on 111.1W. The stuff above is caused by Dish Network's 110W bird. These signals are circularly polarized and one gets a mixture of L & R through the linear LNB.

The second shot is looking through an Invacom QPH-031 quad LNBF using its horizontal output on a GeoSatPro 1.2m offset pointed at 111.1W. There is a lot more cable and switching involved in the signal path, leading to some high frequency roll-off not present with the bandstacked LNB.

One would expect the 1.2m to provide a noticeably better CNR than a 90cm equivalent toroid off-axis by 15 degrees and that is obviously the case. One might also expect a narrower beamwidth on the 1.2m, leading to better rejection of the 110W orbital position. Nevertheless the internal filtering in the bandstacked LNB is much better at attenuating the 110W signals than the non-stacked LNB. Filtering is critical in this particular bandstacked LNB because the out-of-band, higher frequency signals overlap and could easily interfere with both the H & V in-band polarizations.

Pictures are great but there is also real-world comparison. I didn't do this today, but a couple of months ago I did when I was setting up our first SD subscription receiver. I first tried the same Superdish FSS LNB on the T90 and got pretty good reception on 111.1W. However I was concerned with rain-fade and curious how a "higher-end" LNB like the Invacom would do by comparison. So I swapped one in on the T90. The reception was measurably worse on the SD receiver via the Invacom. Back went the bandstacked LNB, and now it may be clearer why this was the case.
 

Attachments

  • 111.1-110W H Bandstacked.gif
    111.1-110W H Bandstacked.gif
    14.9 KB · Views: 161
  • 111.1-110W H NA LNB.gif
    111.1-110W H NA LNB.gif
    15.3 KB · Views: 122
Register Today to see less ads! It's Free!

Tron

SatelliteGuys Master
May 6, 2005
6,599
33
Metro New Orleans, LA
Noise figures don't always tell the whole story. I have a .9 Norsat with a high L.O. stability rating that performs as well as my Invacom .3 Quads. On my 1 meter Channel Master, the Eagle Aspen stacked FSS LNB easily performs as well as a .4 Fortec FSKUV universal LNBF I had on there a long time ago.

Remember, these stacked FSS LNBs were used to receive linear Ku on an undersized dish (the Superdish), and they worked adequately.
 

Mr Tony

SatelliteGuys Pro
Supporting Founder
Nov 17, 2003
291
39
Mankato, MN
I agree Tron
I have an old ExpressVu LNB (when they were linear) that is probably a .7 or .8 and it did better than some so called .3 LNB's ;)
 
Register Today to see less ads! It's Free!
Status
Please reply by conversation.

Users who are viewing this thread

Users Who Are Viewing This Thread (Total: 0, Members: 0, Guests: 0)

Latest posts

Top