"I'm missing one set of transponders."

I have been seeing this posted all over the place lately, mostly with DP or DPP type LNB's.

Here is what could be going on.

On the newer Dish network DP/DPP LNB’s, the transponder frequencies are “Band Stacked” as follows:

• 950-1250 MHz for Odd transponders (12239), or “L”, “H” polarity.
• 1450-2150 MHz for Even transponders (12224), or “R”, “V” polarity.

This enables the LNB to send all the transponders down a single coax at the same time, these LNB’s do not use the +13 volts or +18 volts DC to switch between the transponders from the DP or DPP LNB.

Legacy switches will not work very well with these types of LNB’s, this due to the higher frequency band used for the “Even”, “R” or “V” polarity transponders.
So for the receiver to properly detect the low and high band transponders, it must have the correct settings for this type of LNB, it is usually “OCS-DP” “11250”, the 11250 is the LO frequency (Local Oscillator) used by the LNB to convert a transponder frequency of lets say 12239 MHz, down to something that can be transmitted on a 75 ohm RG-6 coax, this coax must have a 2.5 GHz to 3 GHz frequency response, if not then you will loose out on the higher transponders.


This LO frequency is mixed with the transponder frequency to produce a 3^rd frequency called an IF (Intermediate Frequency), this IF frequency is what goes down the coax to the receiver, if you use the wrong LO frequency your receiver will not be able to properly receive and decode the channels on the transponder.
So lets look at this, take the TP frequency of 12239 MHz, mix it with the LO of 11250 MHz, you then deduct the 11250 from the 12239 (the mixing circuit dose this) to get the IF frequency of 989 MHz, well with in the frequency range of RG-6 coax.


Now for the trick with the band stacking.


With band stacking the even number transponders or the “R” polarities are all put in the higher band and transmitted down to the receiver, what is done is a second LO frequency is used, one that is 500 MHz lower then the first 11250 LO frequency, when mixed with the even numbered transponders you get the second higher band.


So take the transponder 12224R, mix it with the 10750 MHz LO you get 1474 MHz, again with in the range of the RG-6 coax.
The setting for “OCS-DP” or what ever your receiver requires for a DP type LNB, tells the receiver by a software subroutine the correct internal LO frequency to further down convert the IF signal of the selected transponder down to something that can be decoded as a channel or group of channels.


In some cases the use of “Universal” in LNB setting may work sometimes, as most universal LNB’s use two LO frequencies, however the universal LNB needs a 22 KHz tone to switch between the two LO frequencies, the DP type LNB’s do not, they are running both at the same time.


So for those having problems with missing transponders check the following.


Make sure your set to the right LNB type. (most of the time it's "OCS-DP")


Any switch used must be rated for DP Bell or EchoStar products.


Any coax used should be labeled “good to 2.5 GHz” or “Swept to 3 GHz”.


Any ground block needs to be rated to pass 2.5 to 3 GHz.


Any “F” type barrel connector used to connect two lengths of RG-6 coax needs to be rated to 2.5 to 3 GHz.


Any coax jumpers used to connect external or internal satellite equipment needs to be RG-6 rated to 2.5 or 3 GHz, RG-59 coax should not be used.


All outdoor connections and switches should be weather proof or water tight, water when it gets into the coax or connectors will do funny things, some cheap coax has a steel copper plated center conductor, when wet it can rust, this causes problems.


And lastly all systems should be properly grounded; this includes the dish, and any external switches.

And remember the #1 rule of satellite testing “If it ain’t broke, don’t mess with it”.