[Moon] Cabling a dish

[Edward R Cole]

To address the center feedline concept:  the difference in loss is 
negligible (0.36 vs 0.22 dB).  My focal distance is 8-foot so 
supporting with a single center support would be more difficult 
holding the large 23cm feedhorn.  Center feed support would be 
directly in line with center of beam which would be subject to 
scattering off the support.  So which is worse? Center or quad support?

Offset feed is ideal but not easy (cheap) to find larger than 
2.4m.  My surplus 4.9m dish cost me $200 (but don't ask how expensive 
to mount). The 2.4m dish was $100.  1.8m dish (free as it is my old 
sat-TV antenna).

73, Ed - KL7UW

At 12:11 PM 12/25/2015, Edward R Cole wrote:
>Merry Christmas to all eme'rs!  We've had a late Christmas breakfast 
>and my wife will begin making our Christmas Traditional Dinner, 
>soon.  It started our first Christmas of our marriage in 2003 - My 
>special-secret Clam Chowder recipe which was taught me by an old 
>eskimo (yes, there is a story but too long for here).
>
>To answer Sam, I can only tell how I did it on my 4.9m dish.  My 
>feed support is four arms made of 1-inch schedule-40 aluminum pipe 
>(not tubing which is thinner wall).  If doing it over it would be 
>1.5 inch diameter.
>
>I run about 13 foot (4m) of LDF4-50A (1/2-inch Heliax) up the lower 
>of one of the support arms to the W2IDU feedhorn.  I cannot detect 
>much loss at 1296 (theoretically its 0.36 dB or 8% power loss).  My 
>amplifiers are installed in wx-resistant (but not air sealed) boxes 
>on the lower back quadrant about 1.2m from the dish edge.  My dish 
>is solid aluminum sheet made of 16 segments with folded metal to 
>form ribs; each segment is bolted to its neighbor so provide a good 
>support for the boxes by use of short angle aluminum brackets:
>http://www.kl7uw.com/Dish_Oct20-2013.jpg
>http://www.kl7uw.com/Azimuth_Drive_New_2.jpg
>http://www.kl7uw.com/1296PA_withfans.jpg
>http://www.kl7uw.com/1296PA_enclosure_1.jpg
>
>I assume the coax runs do not add significant blockage being 
>attached to the support arms.  My Rx line is LMR-400 run on the 
>other lower arm along with power/control wire to LNA/TRswitch box:
>http://www.kl7uw.com/23cm_LNA_enc.jpg
>
>I have a 2.4m ku-band dish (solid fiberglass) that uses a shepherds 
>crook feed made from WR-90 waveguide with three support wires to the 
>dish to hold the feed centered.  I am not using this dish as no 
>current plans for 10-GHz.  Dish is for sale.  (I have a 1.8m offset 
>feed dish that is probably close to same performance since amp can 
>be located at feed).
>http://www.kl7uw.com/Dish_temp_location.jpg
>http://www.kl7uw.com/1.8m_dish.jpg
>
>I will install my 3400-MHz transverter and amplifiers on back of 
>4.9m dish in similar boxes with same feed line.  For me its easier 
>not to have so much weight at feedpoint and access to boxes is 
>simple for maint. LNA is direct mounted to VE4MA CP feedhorn which 
>will be mounted attached to top side of 23cm feedhorn (slight offset feed).
>
>73, Ed - KL7UW
>
>
>At 11:00 AM 12/25/2015, Sam Jewell wrote:
>>Hi everyone,
>>Please excuse this question, but as I sit here, digesting my 
>>Christmas dinner, I started to wonder about the effects of coaxial 
>>cables in front of a dish.
>>Many of us run dish feeds with the power amplifier behind the dish 
>>rather than at the feedpoint (23cm and 13cm typical). I suspect 
>>most of us then run the transmit feeder ( and receive feeder) down 
>>one of the support tripods to the rim of the dish and then either 
>>back to the centre of the dish rear or maybe away at an angle to 
>>wherever the PA connection is.
>>Clearly the route back to the rear centre of the dish is more than 
>>two times the dish radius and even in the case of my 2.3m dish is a 
>>fairly long run of what might not be the very lowest loss coax size 
>>because of weight constraints.
>>My question is:
>>Is it better to bring the transmit feeder back from the feed to the 
>>centre (hub) of the dish or to keep it off to one side where the 
>>effects of blockage and illumination level are lower, but longer 
>>coax than to the centre?
>>I'd be interested to know what others do before I cut any 
>>(inadvisable) holes in my 2.3m dish mesh?
>>
>>Ohh, and Merry Christmas, if it isn't too late!
>>
>>73 de Sam, G4DDK
>>
>>
>>Sent from my DDKpad
>>
>>g4ddk.com
>>g4ddk.blogspot.com
>>
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>
>73, Ed - KL7UW
>http://www.kl7uw.com
>     "Kits made by KL7UW"
>Dubus Mag business:
>     dubususa at gmail.com
>
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73, Ed - KL7UW
http://www.kl7uw.com
     "Kits made by KL7UW"
Dubus Mag business:
     dubususa at gmail.com