Troubleshooting AFN Broadcast Reception on 4.5 Meter Dish

[Redbull-wings-]

Hello,

We are attempting to get the AFN broadcast on a 4.5 meter (14.7') dish using the following equipment:

- Challenger Communications Prime Focus 4.5 Meter dish (manual Az-El mount)
- Harvard Scientific HS-200 Dual C-Band Feed Horn
- NORSAT 8520 C-Band LNB
- Cisco 9865H Signal Decoder

We've identified two satellites that have footprints that cover our location and are carrying AFN feeds, they are listed below with their respective azimuth and elevation points as calculated by dishpointer.com:
- SES-5 (5.2E): El 44.1, Az 266.9
- NSS-12 (57E): El 75.3 Az 102.3

When we point and attempt to fine-tune the dish for SES-5 we are able to get a signal level of approximately 76-77 and an unstable lock and signal quality of 5-22 which is enough to receive time and the guide but no video/audio.

Pointing at NSS-12 gives similar signal levels of 70-73 but no lock or signal quality.

We're at a bit of a loss on how to proceed, we've spent a lot of time making small adjustments to both azimuth and elevation but haven't been able to significantly increase the level or quality past what's listed above. We have attempted to make adjustments to skew as well by turning the feed horn in its mount but haven't seen any changes in the signal.

Any advice at all on how we might be able to get a stable signal would be very much appreciated, if you have any questions or if I've left any critical information out please query and I'd be happy to provide what I can. Thanks for your time and help!

 

[a33]

So I guess you are in Georgia, Europe, not in Georgia, USA?
Still, for an elevation of >75 to the clarke belt, you would be nearer to the equator than latitude 13 degree.
So that part of your situation is pretty unclear to me...

By the way; Welcome to the forum, Redbull-wings- !

Greetz,
A33

 

[Redbull-wings-]

So I guess you are in Georgia, Europe, not in Georgia, USA?
Still, for an elevation of >75 to the clarke belt, you would be nearer to the equator than latitude 13 degree.
So that part of your situation is pretty unclear to me...

By the way; Welcome to the forum, Redbull-wings- !

Greetz,
A33

Thank you! Good to be here as I learn more about how to get this system working.

To help clear up the confusion, my permanent home is in Georgia, USA but the dish I am working on is close to the equator in Africa. Hopefully, that explains the large elevation to hit NSS-12.

 

[TRG]

Signal levels or quality levels? Signal levels generally don't mean anything. Are you using a meter or a receiver and TV out at the dish?

 

[Titanium]

Is the correct polarity selected? Is the dielectric slab inserted? Fixed or motorized dish?

 

[TRG]

Circular?

https://media.myafn.dodmedia.osd.mil/bulletins/NSS12_CISCO_INSTRUCTIONS.pdf

 

[Redbull-wings-]

Thank you both for your replies!

TRG,
The signal level spikes to about the mid-70s when we start to get a quality level above 0. If quality level is the only figure that matters, we've only seen quality levels above 0 when aiming for SES-5, and even then nothing above about 22. Any quality reading we do receive fluctuates drastically.

We are measuring using the receiver at the dish. I bought a cheap signal meter from Amazon, but we've found using the receiver to provide better feedback. Is this the best way or would you recommend another method?

--------------

Titanium,
The signal from the satellite is LHCP and from my limited understanding, the dielectric plate in the feed horn should convert this to a linear polarized signal for reception by the LNB. We have 18H selected on the receiver and think the skew is set correctly, but it's possible we've set it incorrectly. How do we best check that the skew is properly aligned?

The dish is not motorized and we manually turn and tilt the dish on a pole/hinge for aiming.

The feed horn is a Harvard Scientific HS-200 pictured below:

Edit: Here is the link to the SES-5 parameters and setup as well:

https://media.myafn.dodmedia.osd.mil/afnhd/SES-5_Atlantic_SATNET_Cisco_9865_Settings.pdf

 

[Titanium]

Please take a photo of the feedhorn, the waveguide that the LNB is connected and the dielectric slab as it is inserted into the feedhorn. Do you have one or two LNB connected to the feed? You may be receiving the opposite polarity.

 

[TRG]

Quality is EVERYTHING. Signal only indicates that you have a LNB attached in my experience. According to the documentation this signal is Left-hand circular. In that case you don't need to worry about skew. That's only for linear polarized signals.

 

[Redbull-wings-]

Please take a photo of the feedhorn, the waveguide that the LNB is connected and the dielectric slab as it is inserted into the feedhorn. Do you have one or two LNB connected to the feed? You may be receiving the opposite polarity.

I'll upload the photos tomorrow once I have a chance to take some. I'll be sure to capture the feedhorn, waveguide, and dielectric slab.

We currently have two LNBs connected and have swapped between the two. From our testing, it appears the one that is mounted 90 degrees off from the direction of the waveguide receives the best signal with the other unable to receive any signal quality.

Does having two LNBs connected reduce the signal quality at all? Would it be better to replace one with a metal plate instead?

 

[Redbull-wings-]

Quality is EVERYTHING. Signal only indicates that you have a LNB attached in my experience. According to the documentation this signal is Left-hand circular. In that case you don't need to worry about skew. That's only for linear polarized signals.

Good to know! We'll pay more attention to quality to determine success going forward. Also happy to learn that skew is of no concern when receiving a circularly polarized signal! Do you know if the direction the LNB is mounted matters? i.e. is the relative angle between the LNB antenna and dielectric slab important?

 

[Titanium]

An orthomode feed has a transducer which directs a polarized signal to a specific waveguide (output). Some feeds allow the dieletric slab to be inserted in either left or right hand polarity, while others only allow the dielectric to be inserted into one slot and the LHCP signals are directed to one waveguide output and the RHCP signals are directed to the other waveguide output.

Signal quality is not affected by installing two LNBs, but do not leave an open waveguide. Adding elbows to a waveguide will introduce loss,

 

[Redbull-wings-]

An orthomode feed has a transducer which directs a polarized signal to a specific waveguide (output). Some feeds allow the dieletric slab to be inserted in either left or right hand polarity, while others only allow the dielectric to be inserted into one slot and the LHCP signals are directed to one waveguide output and the RHCP signals are directed to the other waveguide output.

Signal quality is not affected by installing two LNBs, but do not leave an open waveguide. Adding elbows to a waveguide will introduce loss,

That makes sense, in this case, I believe we have the slab glued in place in a slot which explains why one of the LNBs appears to be receiving the correct signal and the other the wrong signal as the polarization is being directed to different waveguides. I'll confirm by uploading some pictures tomorrow.

Really appreciate your willingness to explain these concepts as they've been difficult to find straight answers for online!

 

[Redbull-wings-]

Good morning,

I've attached photos of the feed horn, a shot down the waveguide with a view of the dielectric plate, and a shot of the assembly on the mounting arms of the dish. Of note, the sideways or lower LNB is the one we've had success getting some quality from.

 

[Titanium]

First I will say that it has been years since I worked with circular polarity signals and rarely a Scientific Harvard. Maybe someone else can verify my observation. WIth the dielectric insert installed in this orientation, the rear waveguide output should be receiving a LHCP signal.

Have you checked to see if opposite polarity RHCP signals are being received on either waveguide?

Have you received other transponders? If so, swapped the LNBs to test that both are working?

 

[Redbull-wings-]

First I will say that it has been years since I worked with circular polarity signals and rarely a Scientific Harvard. Maybe someone else can verify my observation. WIth the dielectric insert installed in this orientation, the rear waveguide output should be receiving a LHCP signal.

Have you checked to see if opposite polarity RHCP signals are being received on either waveguide?

Have you received other transponders? If so, swapped the LNBs to test that both are working?

Interesting, sounds like maybe we have a bad LNB in the rear waveguide and the signal we are receiving from the side waveguide is the incorrect polarity and thus reducing our quality. Is there any way to check the polarity received by each waveguide other than seeing which has higher quality for the expected signal?

We've only received from the SES-5's hemi transponder. Is there a way to find others to test with?

 

[Titanium]

Polarity testing and optimization is performed with a live signal. I wouldn't expect to see decoding or a Signal Quality meter reading of a specific on the opposite polarity.

Here is a list of SES 5 transponders and services: SES 5 at 5.0°E - LyngSat

 

[Redbull-wings-]

Polarity testing and optimization is performed with a live signal. I wouldn't expect to see decoding or a Signal Quality meter reading of a specific on the opposite polarity.

Here is a list of SES 5 transponders and services: SES 5 at 5.0°E - LyngSat

Okay, looks like there are a few right-hand polarized signals on SES5 that we should be able to test. I'll let you know what we find as it should help us determine which polarity is connected to which waveguide and whether or not our aiming of the dish is the issue or if a bad LNB is causing our problems.

 

[primestar31]

Okay, looks like there are a few right-hand polarized signals on SES5 that we should be able to test. I'll let you know what we find as it should help us determine which polarity is connected to which waveguide and whether or not our aiming of the dish is the issue or if a bad LNB is causing our problems.

Just swap the lnb's physically between the rear and the side, by unbolting and rebolting. IF one is bad, it should follow to wherever you move it.

 

[arlo]

I see something that may or may not be a problem. But playing around may increase your expected performance.
If in fact your feed is focused for the best possible signal. The throat is very close to the scalar surface plane.
If I were you I would pull the scalar mount and bolt it on top of the extension arms.
That would give a touch more feed throat "stick-out".
It might give you a bit more dish illumination and better signal strength. Worked for me.
Take a gander at the pic. Excuse all of the misalignment. That was all in the process of tweaking for best signal.
I'll guarantee everything is as straight and aligned as can be. Sans the sidecar ku lnbf.

Mine is mounted with a buttonhook feed. So there was a bit of a learning process.
If I were you while moving the scalar to the top of the arms. I would grab some stainless hardware and thin jam nuts. Some bolts long enough to allow moving the scalar in/out.
Start out with the feedhorn pointing directly at the dish center. Pointed at a known transponder.
There are a lot of tricks but I used a couple of paint can tops that telescope into each other. With one that just slips into the feedhorn throat. And use the dimples on the tops to drill holes for a wood dowel. Which ends up with your feed being able to point right at the center of the dish.
Then adjust your dish geometry to get the best signal. It could be as easy as steering the dish E-W a touch or the declination up/down (at zenith).
Then of course a series of feed tweaks and moving the scaler closer or further from the dish.
The scalar plate mounting bolt jam nuts will then let you make tiny adjustments for best signal.

If you are as you describe. On the fringe of the footprint. Perhaps my rant will help you get every last 0.1 dB of signal.
I performed all of the f/D, f, f-this and f-that calculations for my dish.
However a scalar actually functions is all over the place. The rings on a scalar focus and reflect this and that and end up in phase with the feedhorn throat. The rings keep the feed assembly from "looking" beyond the dish rim.
Yeah. I gave up on the theory and concentrated on what works best for me.
Scalar a bit too far in and you get good but a very tight focus and the dish becomes very sensitive to movement.
A bit too far out and the feed assembly loses signal and the signal versus dish movement becomes "muddy" and vague.
My feeble mind relates it to a Newtonian reflector telescope. The diagonal mirror that reflects light from the mirror into the eyepiece needs to be precisely positioned in order for the eyepiece to see all of the mirror and none of the telescope tube. There's your scalar and feedhorn, Mr.

Maybe give it a shot. Can't really hurt. And is definitely reversible.