scanning / LNB / polarization

[gps]

Greetings,

I have a couple of newbie questions if y'all wouldn't mind. Any help would be greatly appreciated.

1. Is there any difference between a LNB and a LNBF?

2. I understand that signals can be vertically or horizontally polarized, and the LNB receives tones from the receiver to activate the individual pickup antenna for a particular polarization. When a scan (blind?) is perfomed, does the receiver sweep both polarizations from the satellite automatically, or must two separate scans be made with a change in polarization setting in between?

Thanks again,
GPS

 

[AcWxRadar]

Greetings,

I have a couple of newbie questions if y'all wouldn't mind. Any help would be greatly appreciated.

1. Is there any difference between a LNB and a LNBF?

Just a little. LNB = "Low Noise Blockdownconverter". LNBF = Low Noise Block Downconverter w/feedhorn.

If you are referring to the assembly on, let's say a DN pizza dish, the part that actually picks up the signal and processes it to be sent to the IRD (Integrated Receiver/Detector) or the STB (SetTop Box) then the part should be referred to as an LNBF because it has a "feedhorn" built into the assembly. It is all one piece, one assembly, so the feedhorn comes with the block downconverter.

For many C-band components, the two are sold separately. So you have the LNB (Low Noise Blockdownconverter) as one part and the F (feedhorn) as the other part. Once you assemble them together they make up the LNBF.

You can generally refer to either component as the same (the terminology is loosely used), but now you understand the technical reference to each. Of course, you cannot refer to the feedhorn alone as either the LNB or LNBF. Alone, the feedhorn is just the "F".

RADAR

 

[Jim S.]

1. An LNB, properly, doesn't have a feedhorn permanently attached. Generally you'll only find these in old and/or professional installations, and mostly C-band.

2. The receiver will scan both polarizations automatically, unless you tell it to only scan one. (Some receivers, you can't.)

 

[AcWxRadar]

Greetings,

I have a couple of newbie questions if y'all wouldn't mind. Any help would be greatly appreciated.

2. I understand that signals can be vertically or horizontally polarized, and the LNB receives tones from the receiver to activate the individual pickup antenna for a particular polarization. When a scan (blind?) is perfomed, does the receiver sweep both polarizations from the satellite automatically, or must two separate scans be made with a change in polarization setting in between?

Thanks again,
GPS

This depends upon the receiver (the IRD or STB) that you have. Most FTA receivers will scan (sweep) one first, then the other automatically. You should NOT have to scan for one then change the selection and scan for the other. Most receivers actually offer the option to scan only one polarity at a time, user selectable, if you wish. But, in auto - scan modes, the receiver will scan both of the polarities without requiring your input or guidance, they do it all for you.

RADAR

 

[RT-Cat]

Greetings,

I have a couple of newbie questions if y'all wouldn't mind. Any help would be greatly appreciated.

1. Is there any difference between a LNB and a LNBF?

2. I understand that signals can be vertically or horizontally polarized, and the LNB receives tones from the receiver to activate the individual pickup antenna for a particular polarization. When a scan (blind?) is perfomed, does the receiver sweep both polarizations from the satellite automatically, or must two separate scans be made with a change in polarization setting in between?

Thanks again,
GPS

First off, WELCOME to satguys. A place where information is just a question away.
.
Most generally the polarity change is a different voltage from the receiver. There may be some LNB's that take tones to change, but I have not run into any yet.

 

[migold]

Polarotors attached to LNBs are controlled by 22KHz signal (Tone), previously used on C-Band by the IRDs. You can still get this type, but most now are using the voltage-controlled LNBFs.

 

[SatelliteAV]

Polarotors attached to LNBs are controlled by 22KHz signal (Tone), previously used on C-Band by the IRDs. You can still get this type, but most now are using the voltage-controlled LNBFs.

I have never seen a 22KHz tone controlled polarotor. Maybe a specialty item? Mechanical polarizers typically are controlled by a variable duration low voltage 5vdc pulse.

 

[RT-Cat]

......Mechanical polarizers typically are controlled by a variable duration low voltage 5vdc pulse.

SatAV, is that how a 920 changes the polarity? I have/use one and was wondering.
RT.

 

[FaT Air]

how to control an analog servo: Supply 5volts to its red wire. The black wire is the negative, and also the common for the control pulse on the white wire. To rotate the output shaft of the servo, supply the white wire with a pulse train with the + pulses duration of anything between 1ms and 2ms. A ~1ms pulse will run output shaft one way, and stop. Supply a ~2ms pulse and the shaft will rotate ~90° from the position it stopped at with a ~1ms pulse and stop there. The timing of the pulse train is a + pulse approximately every 100 to 125ms
___?--?______?--?______?--?___ ~2ms pulses
___??______??______??___ ~1ms pulses
A 1.5ms pulse places the rotation at mid-rotation, 1/2(half) way between where it is with a 1 or 2ms +pulse
Most of the later analog receivers would shut off the pulse train and/or 5v after 5 to 10 seconds to stop servo hunting, "Buzzing" which could/would introduce noise.(Sparklies)
I said an analog servo above, not because they were popularized in the analog video era, but for how their "feedback" is generated to determine it's rotational position. The output shaft is, or is connected to, a potentiometer. (typical analog servo IC: NJM2611)
The R/C enthusiasts are now also using DIGITAL servos where a digital "word", that represents a specific position, is sent to the servo. (only has to be sent once) I think some have 2048 positions in 180° of rotation.
Sorry that got this long, I don't know any way to explain it in just a few lines.
I've heard it said that "The more you know, the more dangerous you are."
Hope this doesn't make any one dangerous in a bad way, lol.