Chaparral C orthomode feed How-To

[Magic Static]

When it comes to C-Band I may be old but not "Old School" So I'm looking for old knowledge about using Chap ortho feeds. When you mount the LNBs is there a particular orientation. They can be mounted one way or 180° the other. Also when orienting the ortho feed on the dish is one polarity always in the center and the other offset? I've noticed things put together in different ways and wondering is there a wrong way and a right way?

 

[Radioguy41]

Go to the FTA manuals section and download the Chaparral manual.

To the powers that be, I have a better copy of the manual and also a printable alignment template for the Chaparral if you want to add it to the repository.

 

[Magic Static]

Go to the FTA manuals section and download the Chaparral manual.

To the powers that be, I have a better copy of the manual and also a printable alignment template for the Chaparral if you want to add it to the repository.

Well I don't see anything about an ortho feed unless it's misfiled somewhere. There's a CoRotor II manual which has nothing to do with my questions.

 

[Radioguy41]

Then I don't understand the question. Your feed is mounted in a Co-rotor scalar and you asked about aligning on the dish and the alignment instructions are in the manual.

 

[Magic Static]

That's an Orthomode feed not a CoRotor if you look closer.

 

[waylew]

I don't believe either case really makes any difference.The LNB probe is going to be vertical or horizontal either way you mount it.The feed orientation shouldn't matter either,either one can be the H or V,just make sure that whichever one is H is attached to the H input and the V goes to V.
The only concern I may have is that the elbow is on top or side to prevent water from being trapped in it.

 

[arlo]

I have a c band ortho here. Pretty much the same orientation as with a 'normal' lnbf. One lnb is H, the other V and so you align it in the scalar with one dead nuts straight up with dish pointing at zenith and go from there like normal. They can work just fine 180 degrees oriented to straight up. Isn't there a zero index and f/D scale on it?

 

[lost_mesa]

IMHO it doesn't matter which way you mount the LNBs to the waveguide on the feed. Either way should give the same results.

For mounting the whole assembly on the antenna, orient it so that the probe in one LNB is exactly parallel to the dish axis (N-S), that will be your vertical polarity. The other LNB probe will be oriented E-W, that will be the horizontal polarity.

One detail, at least on my ortho feed. One LNB is looking directly down the throat of the feed. For the other polarity, there is a probe in the feed throat that picks up the signal and re-radiates it into the second waveguide. I've always assumed that there would be very slightly more loss to this LNB, but don't have anything to back that up. But it doesn't matter which feed port you use for which polarity.

 

[Cham]

On one of mine I installed the LNBs on the feedhorn so the cable connections are closer together for neater cable routing. LNBs are old and the "short" type but likely would mount the same way with the longer "Norsat" types like you have. As Lost_mesa says likely doesn't matter.
I use this feed on a stationary 7' dish but would install the same on a movable one too I suppose.

 

[mr3p]

May I inquire why use a Chaparral orthomode rather than PLL LNBF?

 

[arlo]

Good question. Let's hear it. There's just a ton of Norsat lnbf's and selecting them becomes confusing.
Is it the quest of getting the most sensitive and wide frequency coverage?

 

[Magic Static]

Well to make a short story into an epic:
I've stepped up my interest in FTA with the pandemic and everything. I procured a TBS6903 tuner for the PC and I have learned to use a lot of DVB programs I never used before. Some of the blind scanning I have done with both my C-Band dishes has revealed that my Pinnacle could be a way better dish than it is now. It had a Bullseye II feed on it. It worked OK for what I used it for, my wife actually. It currently has a Titanium PLL LNBF on it, which as far as C-Band goes was a huge improvement over the Bullseye. Of course with a F/D ratio of .286 even the "Fits-All" Titanium LNBF cannot accommodate these deep dishes like it does the not so deep dishes. Yeah the dish with an C-Band Ortho and two $500 Norsat PLL LNBs out performs the Pinnacle with a $40 LNBF on it. Go figure. Since I have access to all kinds of feeds and LNBs for nothing the only thing that's an issue is I can't fiddle with the feed and LNBs while it's on satellite. I need to set everything right to begin with. I noticed the LNBs and ortho feed are not symmetrical in the way they bolt together. SO it brought to mind the question. Is there a right way and a wrong way? I'm not knowledgeable about wave guides and I thought somebody would know more about that than I do. I have an ortho equipped with an optional Chaparral Golden Ring. This ring changed the aperture of the feed opening and was designed for deep dishes. I was thinking of trying it,but I'd like to make sure this is all put together right. That said: I've been reading FAQs at Norsat. Of all the problem solving and tuning issues no mention of how the LNB was oriented to the feed was found. Which supports the findings of many here, it makes no difference in our experience.

 

[mr3p]

I would love to see some data comparing the actual differences between Norsat PLL and Titanium PLL LNBF. I don't doubt the Norsat is better the question would be how much? Maybe Brian has done some comparisons.

 

[MikeI]

Are these orthomode feedhorns for sale? If so, where?

Sent from my LM-G710VM using the SatelliteGuys app!

 

[solarvic]

I used an ADL ortho feedhorn before with good results. It came with a radio shack satelite system I bought that had never been installed. What I wanted was the 100 foot of wire that came with it and I gave the rest to my brother. It worked real well.

 

[Chnlsrfr]

Well to make a short story into an epic:
I've stepped up my interest in FTA with the pandemic and everything. I procured a TBS6903 tuner for the PC and I have learned to use a lot of DVB programs I never used before. Some of the blind scanning I have done with both my C-Band dishes has revealed that my Pinnacle could be a way better dish than it is now. It had a Bullseye II feed on it. It worked OK for what I used it for, my wife actually. It currently has a Titanium PLL LNBF on it, which as far as C-Band goes was a huge improvement over the Bullseye. Of course with a F/D ratio of .286 even the "Fits-All" Titanium LNBF cannot accommodate these deep dishes like it does the not so deep dishes. Yeah the dish with an C-Band Ortho and two $500 Norsat PLL LNBs out performs the Pinnacle with a $40 LNBF on it. Go figure. Since I have access to all kinds of feeds and LNBs for nothing the only thing that's an issue is I can't fiddle with the feed and LNBs while it's on satellite. I need to set everything right to begin with. I noticed the LNBs and ortho feed are not symmetrical in the way they bolt together. SO it brought to mind the question. Is there a right way and a wrong way? I'm not knowledgeable about wave guides and I thought somebody would know more about that than I do. I have an ortho equipped with an optional Chaparral Golden Ring. This ring changed the aperture of the feed opening and was designed for deep dishes. I was thinking of trying it,but I'd like to make sure this is all put together right. That said: I've been reading FAQs at Norsat. Of all the problem solving and tuning issues no mention of how the LNB was oriented to the feed was found. Which supports the findings of many here, it makes no difference in our experience.

FWIW, Chapparal offered in the mid to late eighties , plastic templates which would attached to the lnb flange end of the feed and had embossed into them the proper axis to align the feedhorn to so that the probe ( for polarotor feed) and/or the main axis for ortho feeds was "optimized" in relation to the polar axis of the dish mount. I'll see if I can dig one up and upload a pic.