electronic guys chime in

[truckracer]

I just ordered a corotor for my 10 footer with c and ku lnbs. I know the servo should be controlled my my analog receiver but of course I would have to flip a channel when scanning with my pansat to get the other polarity.

do any of you guys have a schematic that would take the 13v 18v inputs and move the servo?

Does the servo work like this:

No volts - defaults to one polarity (ex Horizontal)
Full 5 volts would be 90 degrees to full Vertical.
any variation of 1, 2, 3, 4 volts would be any angle between.

Do I have this correct?

I can solder and build a circuit that may not reallygive me infinite control but would do the switching. I guess infinite control could be provided with a potentiometer somehow.

 

[Comptech]

I have been following your posts and I had a similar problem with my Ku band. I tried forever and finally gave up.What I wound up doing was putting a dual LNBF on my C-band dish and pulled my 1.2 meter out of storage with its HH120 and put a dual LNBF on it.I use the 922 to move the c-band and the Coolsat to move the ku. I stored all my Ku satellites in the 922 at the same position as G1 so the dish does not move when i switch Ku sats. Works much better than trying to get a good signal from the BCS lnbf.

 

[tvropro]

Study this page, some good basic information:
Servo Basics

Servo's work with a feedback pulse. Hook up a polorotor to an analog receiver and watch what it does when you change polarity and when you adj skew. It moves in steps (adj skew) or the full 90 degrees for V to H. This is all controlled by the feedback pulse width. The three wires are 5V - Pulse - Ground. Without the pulse it won't know where to go.

 

[Hermitman]

It sounds like you need a stepper motor to replace the servo and a control circuit to move it. Below is a webpage with info. I'm surprised someone hasn't already built something like that since many new receivers come without servo control. Maybe the manufacturers want everyone to buy voltage-controlled lnbs. Good luck.

Jones on Stepping Motors

 

[truckracer]

By looking at the schematic you could find the values of the pot or "P1" that sends the servo to either full position polarity and affix a resistor for each value on the circuit and then maybe use some pin diodes to distinguish between 13 and 18 volts. Maybe even keep a pot in the circuit for manual fine tuning.

I will have to think this through. I have an analog receiver to do the job, but I would like a "voltage switching" option.

 

[truckracer]

it seems that some people who have had good luck with the bsc-621 is the ones with smaller than 10 foot dishes. I would imagine maybe with the wider beamwidth maybe these units work better. I am just guessing without any proof or knowledge to back up my claim. Just a theory.

I have ku about as good as I can get it. It seems that as of right now the tp's that fall from 11.7-11.9 come in good. Anything higher than 11.9 the signal starts dropping off pretty fast. That's one reason I can't get the pbs feeds from amc-3ku on my 10 footer.

No amount of tilting, tuning, focal point, f/d adjustments will bring those tp's in any better than 38-40% quality.

On my 7.5' dish with my "frankensein lnbf" that I redneck manufactuered a ku lnbf in the back of an asc-421 c-band only lnbf works like a champ locking the amc-3 pbs tp's in the high 80's.

this 10 footer should do at least that. It has the same mesh. My 7.5' sami has an f/d of .375 where as my 10' has an f/d .38

I would expect the 10' to perform the same or better on ku.
I was attempting to make another ku lnbf mounted in the hole in the back of another asc-421 that i had laying around and damaged one of the probes with the holesaw (I should have paid attention). It works but the c-band part only has one polarity now since i knocked the probe loose and it won't go back in.

 

[truckracer]

I thought about strapping a ku lnbf on the side of my scalar ring and using ku "off axis" and see how that works. Just use some homemade bracket from the hardware store snd strap it on with a hose clamp in the sweet spot. I would have to save the positions for the ku band stuff a few clicks offset from the c-band signals on each bird.

 

[truckracer]

I found this kit online. Is it possible to take the voltage from the coax and apply it to this device maybe using a resistor to drop the volts down to a range of 0-5vdc?

since there are 5 volts difference between H and V line volts could this work?

Here's the link to the kit - Servo Motor Driver

When you flip channels it would move the servo from H to V and vice versa.

 

[tvropro]

I don't know if you want to take the voltage from the coax to achieve this.

Let's look at a few things:

Using a resistor does not always cause a constant voltage plus the load resistor could get quite warm depending in draw. A voltage regulator design is what I would use for a stable voltage.

Pending issues with the above suggestion. Extracting the voltage from the coax line would cause it's own headaches since you have not only voltage but RF on that line. I would think extracting it without a proper L/C design would cause a VSWR change that could cause quite a bit of loss or reflections on the signal itself. Which would kill your signal quality so you would be right back where you were or worse off then where you were with the LNBF.

While things may seem simple on the outside. There's more to it than meets the eye. Without looking at the signal without the proper test equipment it would be hard to design a circuit that is very low loss and achieve the proper isolation.

Now all electronic theory aside. You could give it a shot and see what happens. You could get lucky and be able to toss the textbook right out the window In all my years messing with electronics since I was a 9 year old kid (39 years now) I have found out one thing. Sometimes the simplest things work well.

 

[gabshere]

how about this servo tester

if you had this and a 5 volt battery could you switch the servo on the feedhorn

or a digital version servo tester with a external power adaptor

 

[truckracer]

that's what I was thinking

I figured trying to extract line voltage from the coax would be a real trick.
Not degrading the signal in doing so. Sounds like a simple servo controller with a 5 vdc cellphone ac adaptor and a pot would probably really be the simplest.

I was trying to think of a solution that would not require a large analog receiver. I have an analog receiver, but one day these things are going to be extinct and there are going to be those of us that have servo feedhorns that will need a way to control them.


Our voltage controlled lnbf's have pin diodes that switch the polarity. I do not have a very good understanding of pin diodes (getting ready to search now). I wonder if you could construct a circuit that mimicked the inside on an lnbf to extract the voltage.

 

[tvropro]

You could but it's easier said than done. Can you possibly use a 22k signal to control the servo driver circuit? Just a thought

 

[truckracer]

I wish my work schedule was not so full right now- I am curious and want to experiment.

 

[Hermitman]

Most of the lnbs I've torn apart have a voltage sensing/switching circuit where the coax enters the lnb. The circuit detects either 13 or 17 volts and switches on the appropriate probe circuit in the throat to pick up the signal. After that, there's usually an 8 volt voltage regulator IC that powers the LNB. If you really wanted to tap the lnb power (experiment), you could use a splitter where the coax enters the lnb. From there, have a circuit to block the RF output and feed the voltage to a 5 volt voltage regulator IC to power any switching circuit you want. Good luck.

 

[truckracer]

Thanks Hermit, That is some good info. I knew the lnbf's worked that way and have a good circuit design. I will have to hook one up, tear it apart and get out my digital voltmeter.