Octagon Optima OTLSO PLL Slim Twin Review

In the previous post I reviewed a single output PLL LNB, the Sharp BS1K1EL100A. Today we are going to review a dual output universal PLL LNB, the Octagon Optima OTLSO PLL Slim Twin.

As the name implies, this is an LNB with two outputs, which means you can connect two receivers and tune the same or different transponders on the same or different polarity on the same or different band. This is the LNB type to buy if you want to feed two receivers from a single dish.

The product name says this is a slim LNB. Well, there is nothing particularly slim about this LNB. It uses a standard size feed horn. If you need to place two or more LNB's very closely, it may not be possible with this LNB. To get an idea of what true slim LNB's look like, please take a look at my Inverto Multiconnect LNB solution review.

Dual or twin output LNB's are naturally more complex than single output LNB's. After the low noise amplification stage for both polarities the signal is split and down-converted to individual outputs by two separate mixer, IF amplification and LO circuits. In the following picture one of this circuits is shown, the other one is located below, but the connection to both LNB's is visible. Being a PLL solution, the circuit is very simple with the usual crystal (27Mhz) and IC (RDA3565ES) which incorporates the mixer, IF amplification and  local oscillators. The first stage low noise amplification is done by NE3512S02 HJ-FET transistors which have a NF of 0,35 dB @ 12Ghz. Like most brands, Octagon claims this LNB has a NF of 0.1 dB which simply is impossible to obtain under normal operating conditions. Gain is claimed to be 60-65 dB.

Opening the feed horn I got a bad surprise. As it can be seen in the close-up image, it appears to be oxidation on the signal probes! The tear-down was done with a newly bought LNB shortly after performance tests where carried out. A perfectly sealed LNB should never exhibit signs oxidation. Usually the signal probes are gold coated to prevent any oxidation and signal degradation. After carefully cleaning the probes a new test was carried, but no significant performance difference was observed. This was not unexpected because it is very difficult to measure very small variations of NF.

Tests

The Octagon Optima OTLSO PLL Slim Twin is a good performer. It does not appear to favour a particular part of the Ku band. However, disassembly showed a potential weakness point in the probes. On can only guess if with time this could become a problem.

Sharp BS1K1EL100A PLL LNB Review

The Sharp BS1K1EL100A is a special LNB. Like all universal LNB's, this LNB receives the 10.7-11.7Ghz and 11.7-12.75Ghz Ku bands and looks like a normal single output universal LNB. But inside it hides two characteristics that make this LNB "special". For one thing, this is a PLL LNB. PLL LNB's, as I explained in my previous post, have much higher frequency stability than the more common DRO LNB's. This makes them specially suited to receive low symbol rate transponders. Marketing claims this LNB has an NF of 0.4 dB, 58 dB gain, 25 dB of cross polar discrimination and current consumption between 80-120mA.

To my knowledge this was the first mass market LNB with PLL technology. According to Sharp this is the first LNB in the world with a unique SoC (System on Chip) that integrates in a single IC the mixer, IF, amplification, PLL and LO. Also according to Sharp, this technology allows decreasing the Noise Figure and increasing the Gain linearity. The two local oscillator frequencies needed to receive the full Ku band are generated from a 25Mhz crystal. Inside the IC this 25Mhz frequency is multiplied by 390 (for 9.75Ghz low band) and 424 (for 10.6Ghz high band).

Teardown

This LNB is easy to open. As you can see, it's really small and short. It may be difficult to adjust signal focus on some dishes.

But another difference separates this LNB from the rest. This is due to its unique waveguide geometry. To my knowledge this is also the first universal LNB to use a square waveguide. Until this model came along all universal LNB's have been using a circular waveguide.

Inside the LNB we don't find the common NE3503M04 HJ-FET transistors (typical NF of 0.45dB @ 12 Ghz), but the newer NE3513M04 HJ-FET with practically identical specs. The mixer, IF amplification, PLL and LO IC is marked C520. PCB and component soldering are top quality as is usual with Sharp LNB's.

Tests

This LNB performs well, but apart from the good frequency stability it doesn't really stand out. I noted that it slightly favours reception of the mid to upper part of the Ku band. If you want to receive very weak signals on the lowest frequencies this may not be the best LNB for that purpose, but it's perfectly adequate under "normal" reception conditions. This LNB was sold very cheaply (< 5 Euros). For the price and build quality it's a good LNB.

To learn more about LNB's and PLL technology, please read my previous post on the subject: PLL vs. DRO LNB - Which is better?

PLL vs DRO LNB - Which is better?

LNB's, every satellite TV system uses them. Universal, Ku band, C band, Ka band, single output, dual output, four outputs or even eight outputs, there are lnb's for every need. But essentially, little has changed in lnb technology for almost twenty years. 

One new development has materialized however, the massification of PLL (Phase Locked Loop) oscillator technology. Before we go further let me quickly explain about this oscillator stuff.

LNB's are electronic devices whose purpose is to amplify and convert the extremely weak and extremely high frequency satellite signals into stronger and lower frequency signals capable of being carried over a coaxial cable to the satellite receiver inside your home. To convert a frequency to another frequency an oscillator circuit is required.

Most lnb's use what is called DRO (Dielectric Resonator Oscillator) oscillator technology. And PLL oscillators in lnb's are nothing new, but until about five years ago use of PLL controlled oscillators was restricted to professional use (and expensive) LNB's. This has changed, and now PLL technology can be found on many low cost mass market lnb's. But is it worthwhile? Let's compare both technologies.

DRO technology lnb

Conventional LNB's use dielectric resonator oscillators (DRO) to generate the local oscillator frequencies necessary to down-convert the satellite signal (Ku, Ka or C band) to the IF band used by satellite receivers. These DRO's use pill-like ceramic components glued to the lnb board as part of the oscillator circuit. If the lnb is dual band it will have two DRO's, one for each band. The DRO oscillators are tuned when the lnb is assembled but they are affected by temperature and can drift in frequency. In a mass market lnb, this frequency drift (up or down) can be as high as 3Mhz.

PLL technology lnb

Unlike conventional DRO lnb's, PLL lnb's use a digital (PLL) circuit to generate the local oscillator frequencies needed to down-convert the satellite signal (Ku, Ka or C band) to the IF band. An lnb down-converter PLL circuit is comprised of a chip (IC) and a crystal oscillator. The IC generates the oscillator frequencies from the crystal and then mixes, down-converts and amplifies the resulting IF signal. Commercial mass market PLL lnb's have local oscillator frequency drift from 300Khz to 500Khz.

Benefits of PLL lnb

The main benefits of PLL oscillator technology are frequency accuracy and stability. Since a PLL oscillator is much more accurate than traditional dielectric resonator oscillators (DRO), a receiver connected to an PLL lnb can lock (tune) to a particular signal faster. And while a DRO frequency may drift +/- 3Mhz with temperature, a mass market PLL lnb will usually reduce this drift to a much smaller 300Khz. That's ten times less! 

Local oscillator frequency stability can be an issue when receiving signals. This is specially true when receiving narrow bandwidth low bitrate digital satellite broadcasts. Receivers struggle more to tune (lock) to such transponders, specially ones that use DVB-S2 and low FEC rates. 

For example, assuming your receiver accepts bitrates as low as 1Mbit/s, reliably locking to a 1Mbit bitrate transponder may prove difficult or impossible with a "traditional" DRO lnb. If the receiver is even able to lock to such a signal (probably only after a few good seconds) it will keep loosing signal lock. A PLL lnb will enable the receiver to tune and lock to such a signal reliably, provided the signal is strong enough.

Another benefit of PLL technology is size. Since PLL circuits don't use the relatively big dielectric resonators, the down-conversion circuitry is greatly simplified and much smaller, leading to smaller and lightweight lnb's.

Is it worthwhile to exchange a DRO lnb for a PLL lnb?

It can be, but not always. A PLL lnb is not necessarily better than a DRO Lnb. There are excellent DRO lnb's. You must be aware that other factors besides oscillator stability affect signal quality. For example, it can happen that you install a more stable PLL lnb but its frequency response is not as good as the previous DRO lnb. If you are having trouble receiving low bitrate transponders (like SCPC) then, a PLL lnb could indeed improve reception. However, if all the channels you are interested in are being broadcast in wide bandwidth transponders with high symbol rates (for example 15Mbits or more), then likely little improvement would be gained with a switch to a PLL lnb.

If you would like to share your experience with PLL lnb's please leave a comment!