S Band And L Band Dishes for RUDAK Operations

at WD0E

This page provides an chronology of the development of L and S band capability for AO-40 RUDAK at WD0E, Colorado Satellite Services.

At the beginning of RUDAK operations in May 2001 we were using long loop Yagis for L and S band with RUDAK.  Finding the S Yagi wasn't working properly we switched to an old surplus 4' dish and were able to hear well enough to do a great deal of testing.  That dish was replaced with this 4.5' dish.

It was on a Kenpro/Yaseu G5400 rotor set along with an M2 UHF circular Yagi.  This is a single top section of Rohn 25 mounted on a tilt base that is bolted to a concrete pad.  The tilt base makes it possible to point the antennas up then lay the tower section over onto a saw horse to work on the antennas.  This tower is in the pasture about 40 feet from the operations room and lab.  The 10' dish in the background is for 4DTV TVRO.  The red tractor is a 1949 Ford 8N.

This dish comes in sections nicely broken down for shipping.  It is designed as a 'patio' satellite TV receive unit and includes a ring base and struts to hold it up at an adjustable angle.  The cables here are 9913 for the RF and zip cord for the 12V feed to the preamp.  This is the original S dish only arrangement.

The pedals bolt together and also bolt to brackets that mount on the square plate at the back.  I added a chunk of 1/4" aluminum plate about 18" X 4" to attach the dish to the boom with U bolts.  The angled struts sticking out the back are parts they give you to mount it as a TV dish.  They made a great way to attach a counter weight.  The Down East Microwave transverter was originally just taped to those struts and enclosed in a plastic bag.  The coax from the transverter into the lab is 9913 as well. 

Here is the 1/4" aluminum plate used to attach the dish to the boom.  The only thing I added that was not supplied with the dish is the plate and the U bolts.  The plate is bolted to the square back plate of the dish with bolts that hold the pedal tabs in place.  I added one more for extra stability.  Washers between the square plate and my mount plate were added as spacers to prevent anything from warping.  You can also see here the three tabs used to attach the struts or legs when the dish is used for TVRO.  I used two of those tabs (upper and left) and two of the struts to mount the counter weight.

The holes already in the struts were used to hold them together and mount the counter weight, which is half of an old microwave dish tower mount.  A 1/4" piece of all-thread was bent and used to bolt them together with stop nuts, then the counter weight was added on top.  This arrangement allows the weight position to be adjusted to balance the whole assembly.  The entire thing, less the transverter, weighs 30 lbs.

The dish came with three struts designed to mount a standard Ku TV feed at the focus.   The diameter of the standard TVRO feed is almost exactly the same as this helix feed.  The holes were even the same diameter.  Bolts supplied to mount the TVRO feed were used to mount this S three turn helix.  The Down East Microwave preamp is attached directly to the SMA connector on the feed for minimum loss.  A short jumper of semi-rigid was originally to get us to the 9913.  That cable is stiff enough to support the preamp so there is little stress on the SMA.  The white stuff is RTV to seal the joints.  This little helix feed from Dave Clingerman, W6OAL, the Olde Antenna Lab, on this dish provides enough gain to hear about an S unit and a half of sun noise on a IC-910.  The warm earth is also clearly audible when I drop the dish below about 5 degrees elevation.  Theoretical gain of this feed and dish is about 28 dBic.  Another data point for performance is that I can hear transponder noise on the AO-40 S2 downlink when the bird is at apogee, about 60,000 km range. The 'production' version of this feed has a raydome over it.  Dave built this one for me in a hurry when the loop Yagi wasn't getting the job done and RUDAK needed attention.  

Of course you don't need this much gain to have nice SSB or CW contacts through AO-40.   It is required here to establish solid links to RUDAK for things like loading software when conditions are less than optimum.

Needing more gain for a solid RUDAK uplink we added another identical dish with an OAL helix feed for  L band..

Here is the front of the pair of dishes.  S down on the left, L up on the right.   The nature of the area we live in is evident in this photo.  Properties are 5 acres, rolling hills, few trees except those we plant.  We are on top of a hill so the horizon is zero degrees nearly all around, 2 degrees in the NE quadrant.

This is the OAL helix feed.  It was about 1.5 inches too far from the dish when this photo was taken. This combination provides a theoretical 22 dBic gain.  The FT-736 puts 10W into about 75' of 7/8 heliax which ends at about the height of the az rotor.  That's enough to fully drive the 70W amp which is mounted right on the end of the heliax.  Output goes through about 6' of 9913 to the feed.

This arrangement survived thunderstorm wind gusts to about 40 Mph in bird bath.  However two straight days of 60 MPH winds in January 2002 pretty much destroyed the rotors and some mounting pieces.

June 2002:

Several changes have been made since the original arrangement above was put into service:

The original test feeds from the Olde Antenna Lab were replaced with new ones that include raydomes, both S and L.  The Down East Microwave Transverter has been moved into an electrical box mounted on the tower for weather protection.  The L amp is more or less permanently mounted on the end of the 7/8" hardline and has been sealed with silicon caulk.

The Yeasu rotors were replaced with a much heavier set from M2, the OR2800 and MT3000.

This is a view of the M2 MT3000 elevation rotor.  It's made for large EME arrays and similar antennas.  It appears to have more than enough strength to handle these two dishes.  The TVRO actuator style motor drives a sprocket through a gear box..   A chain wrapped around the D ring through the sprocket and two idler sprockets drive a box cross member to which the cross mast is bolted.  The drive ratio is about 3000 to 1.  Most of the structural pieces are made of 1/4" steal.   Note the double pivot points, one at each end of the horizontal box member.  The cross boom is a piece of 3" aluminum tube with a .25" wall.  The UHF Yagi is mounted on an extension detailed below.  The top of the other three towers at our lab can be seen in the background:  30' sat tower on the left, misc and ATV tower in the middle, HF on the right.

A couple of changes to NOVA were provided by Michael Owen and we are now autotracking LEO birds to less than 1 degree.   The S dish has a 3 dB beam width of about 4 degrees so we are adequately accurate.   The rotors have no trouble keeping up with the lowest elevation birds even on near over head passes.

This is the AZ rotor, an OR2800 from M2.  Very beefy rotor.  Note the thickness of the clamps that hold the vertical mast, a piece of 2" aluminum pipe with a 1/4" wall.  The OR2800 is mounted on a plate a bit stronger than the standard Rohn 25 rotor mount.  The molex connector for the EL rotor is also visible here.  We have pig tails on the rotors and matching ones on the M2 control boxes so we can test and calibrate from the base of the tower, then move the controls into the lab and just plug things together.

A piece of 1.5" fiberglass rod was used to extend the cross boom about 3' to make a mount for the UHF Yagi which is used for receive only.  Rings were machined out of 1" thick aluminum plate and attached to the rod with 5/16" set screws.   This assembly was slipped into the end of the 3" cross mast and secured with 5/16" bolts into holes tapped in the rings.

The extension in place.  I can't claim this as an original idea, M2 made one like it for our ground station at the Air Force Academy.  An extension has also been added to the other end of the cross mast and a Create VHF+ Yagi mounted on it (not shown).

A box was mounted on the side of the tower to contain the electronics in a weather proof enclosure.  It is a standard electrical breaker box with all the guts removed to make it just an enclosure with a handy lift up door.  All the holes in the top and back have been sealed with silicon.  A pair of box aluminum rails bolt to the back of the box and are bolted to cross rails that bolt to the tower with U bolts.  A piece of 3/8" plywood was mounted to the back of the box to make a handy surface for mounting equipment.  The DEMW transverter for S is the aluminum box.  It's powered with 13VDC switched from the shack on spare wires in the rotor cables.  We first tried the power supply for the L amp in the shack using #10 stranded wire to get the DC to the amp.  We found the voltage was about 10V when keyed and power out was only about 25W.  So we put this Astron power supply in the box and ran 110 VAC to the tower on that same #10 wire.  It's connected to an AC outlet in the lower left corner to power the Astron and other equipment or tools we might use in the area.  It's switched from the shack.  This gives us about 65W from the amp at the dish feed.   The box also currently contains the UHF preamp used for receive.

Hopefully this arrangement will survive whatever the Colorado weather has to offer.