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Residential Loop-trough wiring and the DSWM13 w/taps

dswm13 loop-through wiring

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28 replies to this topic

#26 ONLINE   HoTat2


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Posted 21 February 2014 - 07:55 AM


... Channel 1 is the same for "all" @ 974 MHz.

Channel 9 is 1790 MHz, while channel 14 [DSWM] is 1637.39 MHz

Wow ...


Digital SWM technology must really be much more frequency stable than analog.


Doing the math on these numbers, and assuming you can't reduce the necessary transponder bandwidth below the standard 40 Mhz, means a SWM carrier spacing of half that for the ASWM at 51.03 Mhz.  With only 11.03 Mhz of that spacing as guard band as opposed to the 62.06 Mhz spacing needed by the ASWM.


A some 82% reduction in guard band spacing!


Overall in comparison then with only 9 SWM channels into 856.48 Mhz total bandwidth needed for the ASWM, compared with 14 channels into a lesser 703.39 Mhz used for the DSWM, means an almost 90% increase in spectral efficiency for the DSWM!  :)


Very impressive for the DSWM in this respect and surprised DIRECTV wouldn't want to ultimately convert to this technology for LNBFs in the mainstream residential installs.


Anyhow, based on VOS' mention of the DSWM hi-lo SWM carrier frequencies here, it ("finally") looks like the answer to the DSWM13 center carrier frequencies are;


Ch. 1) 974 Mhz

Ch. 2) 1025.03 Mhz

Ch. 3) 1076.06 Mhz

Ch. 4) 1127.09 Mhz

Ch. 5) 1178.12 Mhz

Ch. 6) 1229.15 Mhz

Ch. 7) 1280.18 Mhz

Ch. 8) 1331.21 Mhz

Ch. 9) 1382.24 Mhz

Ch. 10) 1433.27 Mhz

Ch. 11) 1484.30 Mhz

Ch. 12) 1535.33 Mhz

Ch. 13) 1586.36 Mhz

Ch. 14) 1637.39 Mhz

DIRECTV sub. since Sep. of '95

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#27 OFFLINE   slice1900


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Posted 21 February 2014 - 09:43 AM

Here is something that you can do:

Start with a SWiM output fully loaded.

Change all receivers/tuners to the DSWMLNB setting.

If the receivers have actually changed, you will lose one or two tuners.

Channel 1 is the same for "all" @ 974 MHz.

Channel 9 is 1790 MHz, while channel 14 [DSWM] is 1637.39 MHz


An interesting experiment, and one I'll try when I have the chance (though I have only 7 H24s) but I don't think there's a possible scenario where you would lose tuners. Here's why: we don't know how SWM assigns channels to receivers.


There are two possibilities I can think of. It assigns the receiver a SWM channel number (2-9 for ASWM, 2-14 for DSWM13) or it assigns the receiver a specific frequency. Let's assume for the purpose of illustration that setting the receiver for a DSWM LNB makes it really "believe" (act as if) it is connected to one.


If it assigns by channel number, and the receiver was for example assigned channel 3 by the ASWM, since it thinks it is connected to a DSWM it tunes 1076.06 MHz where both DSWM channel 3 and ASWM channel 2 are located. Obviously, it would be unable to change channels since it would be tuning a frequency assigned to another receiver. Since I was able to change channels when I tried this, it is impossible for the receiver to both be assigned by channel number and "believe" the DSWM LNB setting. Thus in this case your test would not lose tuners, because the receiver doesn't the setting.


If it assigns by frequency, then the receiver would work perfectly whether or not it "believes" it is connected to a DSWM. It wouldn't know/care that the channel spacing is different, it would just tune to the frequency provided to it. In this case, your test also would not lose tuners, but unfortunately that would tell us nothing.


So can we tell whether SWM assigns frequencies or channel numbers? I can think of a way, but can't test it myself since it requires access to a DSWM. You'd connect a receiver that has nothing in the firmware for the DSWM and see if it works (either one with old firmware, or perhaps a H20 which "probably" doesn't know about DSWM since it has no setting for Slimline-3DS in current firmware) If it works, and can change channels, SWM must be assigning by frequency. If it fails, it is either assigning by channel number or the firmware refuses to work with a SWM that reports a rev it doesn't recognize.

SL5, PI-6S, SA-6AL, 3xSWM16; 23 H20-100, 7 H24-700/AM21

#28 ONLINE   HoTat2


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Posted 21 February 2014 - 10:31 AM

Well, if DIRECTV's implementation of SWM essentially follows the same channel assignment protocol as outlined in CENELEC's EN 50494, which Entropic uses for the European SWM systems.


The receiver checks with the ODU by submitting *both* the SWM channel number it calculates and frequency it's actually receiving it on for comparative accuracy.


If the ODU responds back that the pairing is incorrect the receiver aborts the process and starts the SWM channel assignment procedure with the ODU anew.  

Edited by HoTat2, 21 February 2014 - 10:34 AM.

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#29 OFFLINE   Stuart Sweet

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Posted 21 February 2014 - 10:36 AM

Veryoldschool is right here, Slice. (Not surprised.)

The only thing you've discovered is that the residential software lets you set the dish type to DSWMLNB when you don't actually have one. The most logical explanation is, as he said, that the multiswitch selection is overriding certain parameters of the LNB selection.

As this thread is just turning into a rerun of this one: http://www.dbstalk.c...nd-speculation/

I'll close it and ask you to direct "theory and speculation" back to that other thread, which is its intended use.
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