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Guest Message by DevFuse

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SWM LNB, No Power Inserter and works OK !


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20 replies to this topic

#1 OFFLINE   fo71

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Posted 16 July 2009 - 07:00 PM

Hi there... my brother recently moved to a new place and ordered DTV. He ordered two receivers, a simple HD and an HD DVR. The installer came and everything ok. I visited this last week and while there he realized DTV had quit working. We tried to troubleshoot. First I checked connections and cables all was as the installer had left them. I then decided to check if the power inserter was connected to power and to my surprise I couldn't find one, very strange. Where did the SWM LNB get power from?

After looking at all connections and cabling thoroughly his girlfriend arrived and said she had "unplugged" the non DVR receiver from the outlet to put a power strip in place, she needed extra outlets for a table lamp and the strip was off, meaning the H23 receiver wasn´t getting power. We´ll as soon as we turned the strip on, we heard noise from the set at the living room.

WOW, the H23 is not only a receiver but also serves as power inserter for the SWM lnb. Not convinced I unpluged the coax cable from the H23 and signal was lost at the living room, reconnected and came back.

What a neat surprise, has anyone seen this before?

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#2 OFFLINE   RobertE

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Posted 16 July 2009 - 07:13 PM

It's not going to last or work for long.

Seem as if the H23 is putting out just enough volts to power the SWiM LNB. Something is going to give up the ghost before long.
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#3 OFFLINE   carl6

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Posted 16 July 2009 - 11:04 PM

I agree. The H23 is capable of providing a limited amount of power, but I don't think it is designed to power an SWM LNB (although I don't know that for sure). I suspect the power draw of the LNB could result in premature failure of the H23.

#4 ONLINE   armophob

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Posted 16 July 2009 - 11:40 PM

But at least you know it is girlfriend proof now.:)

#5 OFFLINE   avmaster

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Posted 17 July 2009 - 12:00 AM

Your going to burn up either the reciever or the swm splitter, get that power inserter on there pronto.

these boxes put out either 13 or 18v dc, its getting powered up by that. The power inserter is 21v.

Guess what happens when you try to power something that calls for 21v off of something that puts out a lower voltage?

Your current increases. So the reciever is trying to push more current that its deisigned for. Its not if its going to fry it, but when.

#6 ONLINE   veryoldschool

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Posted 17 July 2009 - 07:38 AM

I agree with all, get the correct PI for the SWMLNB.
"I would guess" when receivers are tuned to channels that cause them to output 18 volts, that the SWM works. I'd also guess when they change to 13 volts, it will not.
The PI is rated @ 21 volts 1.2 amps/25.2 watts
Receivers are outputting 13/18 volts and about 450 ma.
A.K.A VOS

#7 OFFLINE   fo71

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Posted 17 July 2009 - 11:53 AM

Thanks for the advice guys, will till my bro to get a power inserter to put it in place.

Quick thought, looking at the specs you guys posted for the PI, I have in my old box of junk a power supply that came with an eagle aspen 4x8 multi switch. It is rated 24VDC at 1.2 amps Would that work if connected it to the power passing leg at the SWM splitter? I'd then just connecto both receivers to non-power passing legs.

Thanks !

#8 OFFLINE   jamesgangnc

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Posted 17 July 2009 - 12:09 PM

Actually when you power something with a lower voltage the current decreases. Review your ohms law. But I agree it should be set up as designed.

#9 OFFLINE   evan_s

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Posted 17 July 2009 - 12:31 PM

Thanks for the advice guys, will till my bro to get a power inserter to put it in place.

Quick thought, looking at the specs you guys posted for the PI, I have in my old box of junk a power supply that came with an eagle aspen 4x8 multi switch. It is rated 24VDC at 1.2 amps Would that work if connected it to the power passing leg at the SWM splitter? I'd then just connecto both receivers to non-power passing legs.

Thanks !


That would probably work. The early Power inserters for the swm8 were 27 volt and they work fine with the swm lnbs. I'd still probably buy the right one. They aren't that expensive and no reason to risk a problem.

#10 OFFLINE   RobertE

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Posted 17 July 2009 - 12:44 PM

Thanks for the advice guys, will till my bro to get a power inserter to put it in place.

Quick thought, looking at the specs you guys posted for the PI, I have in my old box of junk a power supply that came with an eagle aspen 4x8 multi switch. It is rated 24VDC at 1.2 amps Would that work if connected it to the power passing leg at the SWM splitter? I'd then just connecto both receivers to non-power passing legs.

Thanks !


It may or may not work, even if it does, who knows what sort of RF noise it may put on the lines.
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#11 ONLINE   veryoldschool

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Posted 17 July 2009 - 12:48 PM

Actually when you power something with a lower voltage the current decreases. Review your ohms law. But I agree it should be set up as designed.

I think when the load is doing work, you need to look at Ohm's law as it pertains to watts.
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#12 OFFLINE   fo71

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Posted 18 July 2009 - 05:56 PM

OK.. just to keep you updated...

...the Eagle Aspen power supply worked fine. Couldn't tell of any problem, however following your advice, I picked up a DTV power inserter last night at a local distributor. They explained there are two types of power inserters (PI) for SWM. The 21 volt version (PI-21) to power un SWM lnb's. There's also the 28 volt version (PI-28) to power SWM 8 switch.

This morning I headed out again to my brother's palce, put in place the PI-21and all is well. Thanks again for all your valuable insight and support.

Until next time, my best.

#13 OFFLINE   jamesgangnc

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Posted 20 July 2009 - 12:09 PM

The load, in this case the lnb, behaves like a fixed "resistance" to the flow of electricity. At a higher voltage more current will flow than at a lower voltage.

Watts is the current times the voltage. As the voltage increases over a fixed resistance the wattage will increase exponentially. As the voltage decreases the reverse happens.

volts ohms amps watts
10 1000 0.01 0.1
20 1000 0.02 0.4
30 1000 0.03 0.9
40 1000 0.04 1.6
50 1000 0.05 2.5
60 1000 0.06 3.6
70 1000 0.07 4.9

#14 OFFLINE   houskamp

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Posted 20 July 2009 - 12:11 PM

Simpler way to look at the overload:
legacy system only powers the switch and the one lnb it needs..
SWM has all the lnbs plus the switch powered at all times..

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#15 OFFLINE   hdtvfan0001

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Posted 20 July 2009 - 12:25 PM

Simpler way to look at the overload:
legacy system only powers the switch and the one lnb it needs..
SWM has all the lnbs plus the switch powered at all times..

A great way to explain it!
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#16 ONLINE   veryoldschool

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Posted 20 July 2009 - 12:34 PM

The load, in this case the lnb, behaves like a fixed "resistance" to the flow of electricity.

Guess I was getting lost thinking about "load/work" as it is in a motor where the resistance isn't fixed.
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#17 OFFLINE   evan_s

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Posted 20 July 2009 - 01:30 PM

The load, in this case the lnb, behaves like a fixed "resistance" to the flow of electricity. At a higher voltage more current will flow than at a lower voltage.

Watts is the current times the voltage. As the voltage increases over a fixed resistance the wattage will increase exponentially. As the voltage decreases the reverse happens.

volts ohms amps watts
10 1000 0.01 0.1
20 1000 0.02 0.4
30 1000 0.03 0.9
40 1000 0.04 1.6
50 1000 0.05 2.5
60 1000 0.06 3.6
70 1000 0.07 4.9


I assume that there is some sort of DC to DC regulated or at least semi regulated power supply in the LNB assembly. I highly doubt they are powering the ICs for SWM directly from the 20+ volt power the PI is providing. Assuming that is the case it would indeed draw more current at a lower voltage.

#18 OFFLINE   houskamp

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Posted 20 July 2009 - 01:38 PM

I assume that there is some sort of DC to DC regulated or at least semi regulated power supply in the LNB assembly. I highly doubt they are powering the ICs for SWM directly from the 20+ volt power the PI is providing. Assuming that is the case it would indeed draw more current at a lower voltage.

Actualy it would stay dead even (at least till VR circuit colapses) as the voltage it is actualy using would stay the same..
depending on the VR type, most likely a 7800 type (analog) regulator, 30v dropped thru VR to 5v at 500ma= 10v dropped thru VR to 5v ay 500MA..both would pull 500MA..

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#19 ONLINE   veryoldschool

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Posted 20 July 2009 - 01:41 PM

Actualy it would stay dead even (at least till VR circuit colapses) as the voltage it is actualy using would stay the same..
depending on the VR type, most likely a 7800 type (analog) regulator, 30v dropped thru VR to 5v at 500ma= 10v dropped thru VR to 5v ay 500MA..both would pull 500MA..

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#20 OFFLINE   cartrivision

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Posted 05 August 2009 - 03:39 PM

When I accidentally discovered the phenomenon of the SWM working without a power inserter, I pulled out my multimeter to do a little investigation. Here's what I discovered:

(+) The HR2x DVRs seem to always send about 13 volts up the coax when operating in SWM mode. They apparently never send 18 volts as voltage switching isn't done while in SWM mode.

(+) The SWM "seems" to operate without any issues from the 13 volts that is supplied by the DVR.

(+) The DirecTV SWM power inserter will block upstream DC so if you have a power inserter between the voltage supplying DVR(s) and the SWM, losing power at the inserter will shut down the SWM as none of the DC voltage coming from the DVR will get past the power inserter to the SWM.

(+) The "Ideal" brand 4-2300Mhz 2-way satellite splitters that are sold at Home Depot pass the DC voltage up the line to the input from BOTH outputs, despite markings on the splitter that indicate that only one output is power passing. They do however block power passing from output to output, which is necessary when the power inserter is not placed before the first splitter.


My next project is to measure the actual current draw when the DVR is powering a standard LNB vs. when it is powering the SWM LNB to see whether or not it looks like there is any need to be concerned about overloading the DVR's power inserter circuit if the SWM power inserter isn't supplying voltage to the SWM.

It seems to me that if powering an SWM with a DVR had the potential for creating an overload problem, DirecTV wouldn't (or shouldn't) be sending any DC up the coax line while a DVR is operating in SWM mode, as there is no way to guarantee that an SWM power inserter that is installed downstream from one or more DVRs won't lose power while the upstream DVR remains powered up and operating.




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