Help with Blonder Tongue LDA-50

[mjahall]

Hello,

I have a small hospital group with 5 patient rooms that each have a digital receiver off DirecTV. Seems any time two TV's are on, all is fine. When the third or fourth go on, others drop out. DirecTV was out and said it was due to the legnth of cable between the roof (14 floors of RG-11) and receivers, and were receiving a -60 at the splitter outside the first patient room. They said I needed an Amp.

Blonder tongue rep sold me an LDA-50, L-band amp. WHen I installed it up at the roof level, nothing worked. I was then told it was because I needed a Power Inserter, as the LDA-50 did not pass power to the LNB's. DirecTV came out and moved the Power Inserter (PI -21), to the LNB side of the amp and we still had no signal at all down at the receivers, (whereas we had some signal with no amp). 120VAC Power to both the PI and amp is good.

I noticed that the antenna had 3 LNB's attached. DirecTV said this is to get multiple satelites. Yet I saw only one trunk cable. Does this sound right? Can anyone offer any advise on what I can try next?

Thanks!

Joe

 

[Joe Diamond]

The single line from the Dish / LNB indicates a Single Wire Multiswitch as partof the dish equipment. The single line is ok.

What else is installed between the first receiver and the dish?

That Blonder Toung is a top quality cable splitter...what are its' characteristics?

Fourteen floors of RG11 exceeds the capacity (cable length) of the SWM equipment. You might want to take this question to the the MDU (Multiple Dwelling Unit) forum or contact Sonora Equipment...they do this stuff all the time.

Also Joe

 

[mjahall]

Thanks Joe. There is an eight way splitter between the first receiver and the dish. as I go up from the receivers, there is the PI and then the dish.

If I take the amp and install this where as the output looks toward the receivers and the input faces the PI. The swm side of the PI then faces the dish. I get no signal.

 

[Bob Nielsen]

Will that amp pass the 2.3 MHz SWM control signal (reverse direction)? The specs don't mention it. Here's one which does: http://www.techtoolsupply.com/ProductDetails.asp?ProductCode=LA141R

 

[jjnemoiii]

LA141a
I use the Sonora LA141a, works great for me, although it previously was made in the USA. Works great for DirecTV, including HD.

 

[AntAltMike]

The Blonder Tongue amp does NOT pass the return signal, but it does have a lot more gain than does the Sonora amp, and a higher maximum output level.

If you want to use the Blonder Tongue amp, you can use two STD-9501 NAS diplexers to loop the return signal around it, but you might still be overloading it.

Roughly speaking, the SWM LNB has an output signal level of -31dBm with 15 dB of AGC to keep it relatively stable eve3n during rain fade. A well designed system delivers at least -55 dBm to each receiver. You lose around 12dB through the eight way splitter, and then you have your cable losses to factor in.

The LDA-50 has a gain adjustment of 37 to 52 dB at 2GHz, and a maximum output of 1dBm, so even if you put it at the bottom of a 200' RG11 trunkline, you will need to turn the amplifier gain all the way down and you still might wind up overdriving the receivers, since they probably will not perform reliably if their input is stronger than about -20dBm. Basically, the Blonder Tongue has so much gain that it presents an engineering challenge for you that may be too much of a nuisance for you to deal with. If it were mine, I'd put it at the bottom of the trunline, loop the sub band return signal around it, and put a 10dB pad on the input and another 10 dB pad on the output.

The Sonora amp only had about 14dB of gain and a maximum output level of about -14dBm. You can probably drop it in anywhere. If it were mine, I'd put it at the bottom of the trunkline rather than at the top, but before you buy one, do the loss arithmetic for your RG11 trunkline at 1,800 MHz, plus the published splitter loss, plus the RG-6 drop line loss to make sure you are still above -55 dBm at each receiver. If you are not, then you may need to use two of them: one at the rooftop and one near the splitter.

 

[jjnemoiii]

"If it were mine, I'd put it at the bottom of the trunkline rather than at the top"

AntAltMike, I guess I do not understand amps as well as you. I always thought you were to put the amp as close as possible to the antenna or dish, thus amplifying the strongest signal you have, rather than trying to amp up a weaker signal down below. I assume I am missing something or misread something in the past...

 

[AntAltMike]

"If it were mine, I'd put it at the bottom of the trunkline rather than at the top"

AntAltMike, I guess I do not understand amps as well as you. I always thought you were to put the amp as close as possible to the antenna or dish, thus amplifying the strongest signal you have, rather than trying to amp up a weaker signal down below. I assume I am missing something or misread something in the past...

The advice of putting a preamp as near as possible to the antenna applied to most off-air, analog reception situations, where all of the signals were weak and we were trying to maintain a signal to noise ratio above 45dB. With digital signals, they already are preamplifed about 50dB by the LNB, and are about a thousand times as strong at that point as they need to be to adequately supply a DBS receiver, and also we are only trying to maintain a signal to noise ratio of about 8dB. As you increase an amplfier's load, the intermodulation distortion increases as the square of the increase in load, so basically, if you put the -31dBm signal coming out of an LNB into an amplifier with 50 dB of gain, the output of that amplifier will approach 20dBm, which is a hundred times the maximum rated output level of that amplifier, and it will be so distorted that is will no longer be processible.

The Sonora amp has been engineered so that it can be placed right after the LNB, but I prefer to put it downstream to reduce the intermodulation distortion.

 

[jjnemoiii]

Thanks for the lesson!