Noob in the deep end. Some help here? ;)

[jugghedd]

I wanted to try and do some C band and already had the BC621 2D so I decided to post an ad to see what I could find. Long story short, I got an 8 foot andrews solid dish with some sort of feed arm on it. Sorry for my lack of proper terminology. But, its a long arm thats shaped like a shepard's hook.
The exact one in the picture. Dish and arm. So, I'm wondering if I could buy something that goes on the back to receive the signal fed through the arm or if I need to remove it and mount the 621 LNB on some sort of tripod setup. I obviously need to mount it still. But, I have diagrams how to do that. Im wondering more how that arm functions and if it can be used with C band. Seems sad to trash the original setup unless I have to. That arm is all copper and looks really cool too.

 

[Anole]

I think that's a terrestrial microwave dish.

There are a lot of us who can give you great suggestions on retrofitting it with three or four arms and a scalar.
However, if you hold off, maybe one of our guys with commercial experience might have pertinent advice.

Another area of concern is the back side.
You would be best served if you can mate it to a polar mount.

 

[jugghedd]

After looking at the whole thing again, I realized I have the original catalog the guy gave me. Its from 1976 but has all the parts shown. I think that arm is called a waveguide? and possibly the part I need is a transition to type N jack. Feel free to correct me. I feel a little lost

 

[Anole]

Yes, it's a waveguide.
Does it mention what frequency or band it's designed for?

Technology has progressed a bit in the ensuing 3-4 decades.
We no longer pipe our microwaves around any more than necessary - too much loss.
Now we put the whole receiver front end right at the focal point of the dish!
N-connectors are only part of history.

 

[SatelliteAV]

The unit is for terrestrial microwave and the model number will reveal the operating frequency range. The arm is likely an integrated feedhorn and waveguide that directs the signal to the electronics located on the back of the dish. It would be a single polarity and cut for a frequency that is likely outside of the desired satellite frequencies.

The dish is probably best suited for a fixed az/el mount and retrofitted with legs and either a feedhorn/LNBs or a LNBF.

Edit: The thread grew after I walked away from the desk...

 

[jugghedd]

it just says TYPE F8A. Still looking for it in the catalog for more info on it.

 

[jugghedd]

So one more question I think I know the answer to. Could I use the arm as a mount instead of the tripod? Its really stable. I wonder if it would interfere. I would think the focal point is right at the plastic lense on the hook and could maybe mount it there or cut it off so it could be centered well somehow. Sorry for so many possibly dumb questions and thanks for all the quick help. Im definitely gonna find a signal on this puppy somehow.

If by polar mount you mean on a pole, that was my plan. Up on the hill in the back of my property sorta low to the ground but high enough to clear most angles on the dish

 

[SatelliteAV]

Sorry, Andrews Type F8A doesn't mean anything to me (or Google)! Maybe someone else might recognize this.

Purposing the existing arm for hanging a feedhorn or LNBF might be a good idea. Figure out the FD and verify that it is in the correct sweet spot.

 

[FaT Air]

Should be able to see if the waveguide will operate at satellite frequencies. http://www.rfcafe.com/references/electrical/waveguide-chart.htm
If it's WR229 waveguide a standard C band lnb should 'bolt right on'. (but not the BSC621)
NOTE: An LNB will only get you one polarity.
Off subject:

We no longer pipe our microwaves around any more than necessary - too much loss

Not true. A waveguide has the lowest loss possible to 'guide' rf from somewhere to somewhere else. But technology has progressed to a point it's no longer necessary to do that. Receiving electronics are now so physically small, it can be placed right behind the focal point, with the antenna [probe] in a short waveguide placed optimally at the focal point. (Transmitters normally still employ waveguides, especially high power ones)
BACK on:
Mount the BSC621 so the throat of the feed is about 1/4 inch closer to the dish that what's calculated for focal length. Set the scalar to what's calculated for F/D ratio. Note: may have to adjust closer/further from the dish as there's measurement errors / manufacturing variances. But should be close enough to 'get going'.
http://www.satellite-calculations.com/Satellite/reflector.htm
Electrical conduit for legs?

 

[KE4EST]

Wow N-Connectors have not messed with those in years.

 

[jugghedd]

Goin out to play! I'll send updates later or tomorrow. Thanks a lot guys! I have a lot to try, and learn.

 

[ZetaMale]

I wanted to try and do some C band and already had the BC621 2D so I decided to post an ad to see what I could find. Long story short, I got an 8 foot andrews solid dish with some sort of feed arm on it. Sorry for my lack of proper terminology. But, its a long arm thats shaped like a shepard's hook.View attachment 87081
The exact one in the picture. Dish and arm. So, I'm wondering if I could buy something that goes on the back to receive the signal fed through the arm or if I need to remove it and mount the 621 LNB on some sort of tripod setup. I obviously need to mount it still. But, I have diagrams how to do that. Im wondering more how that arm functions and if it can be used with C band. Seems sad to trash the original setup unless I have to. That arm is all copper and looks really cool too.

It is a button hook style feed. It is a waveguide coming out of the center of the dish to the feed point. The orientation of the waveguide determines polarity. You won't be able to change polarity with an LNBF or LNB due to the fixed polarity of the waveguide/feed orientation - you would have to rotate the entire dish 90 degrees to change polarization. Someone mentioned electronics on the back of the dish but I have never seen any electronics on the back of this dish in my 30+ years of microwave radio service. Only waveguide, elliptical or rectangular, from the back of the dish to the radio is what you will usually find but transitions can be used to change from waveguide to coax. Waveguide will have less loss though. But, there may be modification kits to do things with this dish that I'm unaware of. But, I would imagine that such mods won't be cheap.

 

[ZetaMale]

Should be able to see if the waveguide will operate at satellite frequencies. http://www.rfcafe.com/references/electrical/waveguide-chart.htm
If it's WR229 waveguide a standard C band lnb should 'bolt right on'. (but not the BSC621)
NOTE: An LNB will only get you one polarity.
Off subject:Not true. A waveguide has the lowest loss possible to 'guide' rf from somewhere to somewhere else. But technology has progressed to a point it's no longer necessary to do that. Receiving electronics are now so physically small, it can be placed right behind the focal point, with the antenna [probe] in a short waveguide placed optimally at the focal point. (Transmitters normally still employ waveguides, especially high power ones)
BACK on:
Mount the BSC621 so the throat of the feed is about 1/4 inch closer to the dish that what's calculated for focal length. Set the scalar to what's calculated for F/D ratio. Note: may have to adjust closer/further from the dish as there's measurement errors / manufacturing variances. But should be close enough to 'get going'.
http://www.satellite-calculations.com/Satellite/reflector.htm
Electrical conduit for legs?

Waveguide is unnecessary because the LNB/LNBF block converts the microwave freqs down to around 900 MHz where waveguide isn't required.

 

[jugghedd]

So my experimentation ended pretty quickly. I had trouble trying the 621 on a small dish. Im having the same problem. Seems like my SAT meter just screams even on low sensitivity. And it doesnt change much with angle or anything else. I may just try a c band only LNBF. That thing just doesnt act right unless Im missing something. I should be able to use the same meter I use for Ku right?

Also, I think I may just use the arm for the mount. It does appear to clamp nice at where it needs to be and I wont have the polarity problems.

 

[jugghedd]

I made some progress slowly this morning. Still not all the way there. But, a little closer. I think the lead on my meter was way too short. Around 3 foot. I noticed that moving my hand or the wire or anything made the signal jump. I put a longer lead on and now Im getting more consistent results. I guess I underestimated the background signals. They seem to be everywhere with the big dish. Or just "noise" of some kind in general affecting the meter.

So the next question (sorry) I have is: Should I use the conical scalar with a prime focus setup like Im trying to do or is it only intended for offset? I have both a flat and conical scalar ring.

 

[Lak7]

Should I use the conical scalar with a prime focus setup like Im trying to do or is it only intended for offset? I have both a flat and conical scalar ring

Flat Scalar for Prime Focus.

Try to get meter behind the dish.

 

[truckracer]

I remember seeing those wave guide pipes flanged together

 

[SatelliteAV]

Someone mentioned electronics on the back of the dish but I have never seen any electronics on the back of this dish in my 30+ years of microwave radio service. Only waveguide, elliptical or rectangular, from the back of the dish to the radio is what you will usually find but transitions can be used to change from waveguide to coax.

Isn't the transition device from wave guide to coax electronic?

 

[jugghedd]

after reading through the old catalog I don't think I can use the waveguide. its a rectangular one and I think thats single polarity if I understand right.

 

[SatelliteAV]

The shape of the waveguide and feed is tuned to a specific frequency range. This is a limiting factor for the band that the dish is currently able to efficiently receive .

The orientation of the feedhorn / waveguide assembly determines the polarity. The entire dish would be rotated to adjust the polarity or skew. You are correct, as we previously pointed out, the feedhorn design only supports a single polarity.