LINDENBLAD CONSTRUCTION SEMINAR FOLDED-DIPOLE LINDENBLAD VERSION By Ron Herring W7HD Version dated 23-Oct-2016

BUILDING A LINDENBLAD What is a Lindenblad? It is a circularly-polarized antenna with an omnidirectional pattern. Gain is about 9 dB

Lindenblad Characteristics With most of its gain at low elevation angles, it is ideal for accessing low earth orbit (LEO) Amateur Radio Satellites. It is also a good general purpose antenna for FM/repeater and SSB or CW operation. This type of antenna was devised by Nils Lindenblad of RCA around It's purpose was to provide solid copy of a weather satellite.

Lindenblad description What is it? The Lindenblad antenna consists of four half-wave folded dipoles slanted 30 degrees to the horizon, oriented 90 degrees to each other in azimuth, spaced 0.3 wavelength apart. They are tied together by four half wave 300 ohm twin-lead lines that divide the folded dipole's impedance by four where they connect to the coax feed line.

Radiation pattern EZNEC radiation pattern of Lindenblad antenna.

Radiation pattern Since the Lindenblad has the most gain (about 9.7 dBi) from about 5º to 35º above the horizon, it is perfect for most satellite passes. Although it has 0 dB gain vertically, that is offset by the signal strength of the satellite, so the net result is good copy almost from horizon to horizon. It is also good for SSB/CW and FM repeater operation. My 2M Lindenblad works well for the nearby repeaters within 60 miles, including the 440 repeaters!

Lindenblads installed at FAA control tower in Merced, CA

Other types of Lindenblads What we describe in this presentation is the folded-dipole version of the Lindenblad. There is also an EZ Lindenblad that consists of a vertical dipole surrounded by parasitic half-wave elements arranged in the similar 30º offset pattern. It is very easy to build and has less wind loading, hence its name. See my website article: lindenblad.pdf I have built several of those, too, and they work well, although my experience has been that the folded-dipole version, although more complicated to build, is slightly better.

70cm EZ Lindenblad. This is a working version I used to make a contact on SO-50.

My homebrew twin-lead 70cm Lindenblad

2M Lindenblad parts

70cm Lindenblad parts

The differences between the two The only difference between the two antennas is the length of the PVC pipes. Estimated cost for all the parts at your local hardware store is about $30. I used 3/4” Schedule 40 PVC parts. Making the dipoles consists of taking 4 FM Dipoles (about $4-$6 each) and cutting them to length and marking the right-hand lead of each.

Parts List 8 ea 6” element support for 70cm or 18” for 2M 4 ea 3-1/4” spacers for 70cm or 10-1/8” for 2M 4 ea 3-way tees 1 ea 5-way cross 8 ea end caps 1 ea PVC coupler to connect the support pipe 1 ea PVC support pipe of your desired length (mine is 12”) 4 ea FM dipoles (or make your own) 1 ea female bulkhead F-connector Suitable length of RG-6 coax

How to build it First cut all the parts to length. Make sure to remove any burrs or sharp edges. Next, cut the dipoles to length. Make sure to put a spot of glue or epoxy in the center tee of the dipole to hold it in place. Give it time to dry. They will easily pull out if you're not careful. 11-1/8” for 70cm and 33-3/8” for 2m. Place a paint dot on the right side of the twin- lead at each end. 70cm element covers are 6” length and 2M element covers are 18” 70cm spacers are 3-1/4” and 2M spacers are 10-1/8”

Assembly Method Cut dipoles to length, adding about 1/4” at the end for stripping and soldering them together.

Assembly Method Cut phasing lead to length.

Assembly method First, you will insert the dipole element in a tee with the phasing lead out the center and one element support pipe. Leads are not yet cut in this photo. You will want that done beforehand.

Assembly Method Then, add the second element support pipe.

Assembly Method Route the phasing lead through a spacer pipe.

Assembly Method Add the 5-way cross

Assembly method Repeat for each folded-dipole element until all four are attached with the phasing leads coming out of the center of the 5-way cross.

F-connector wiring Now connect all the marked dot leads to one lead of the female F-connector. Connect the remaining leads to the ground side of the female F-connector.

Final assembly Put a small amount of Penetrox or DeOxit on the F-connector threads to insure good contact, then connect the RG-6 cable and route it through the support pipe that you will now insert into the center of the 5-way cross. Insert the end caps on each element. Rotate each element to 30° off horizonal before fastening. Far end down for right-hand circular, up for left-hand circular polarization. Add the PVC support pipe (mine is 12” long), finish painting it, and let it dry! You may wish to use a small #6 x 1/4” sheet metal screw to hold each PVC connection in place for stability instead of gluing them. Be sure to tap the ends to insure they are fully seated before fastening or when gluing. Mount the support pipe using a pair of u-bolts to a mast or pole, connect the RG-6 to the radio using a F-male to BNC or PL259 adapter and let the fun begin.

THANK YOU You can download my PDF of the assembly instructions at this URL: lindenblad.pdf And the presentation powerpoint here: You may wish to check back now and then, since I do update my instructions as I discover ways to improve it.

My website contains a large amount of information for the amateur radio operator. Our club website by Bob AF9W URL: ENJOY – Ron W7HD The End