LINDENBLAD CONSTRUCTION By Ron Herring W 7 HD

LINDENBLAD CONSTRUCTION By Ron Herring W 7 HD A PARASITIC LINDENBLAD for VERY easy construction. This version is for 70 cm. 1

Other types of Lindenblads What we describe in this presentation is the parasitic version of the Lindenblad. It consists of a vertical dipole surrounded by parasitic halfwave 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 for details: http: //w 7 hd. ddns. info/sats/building-the-70 cm-lindenblad. pdf The folded dipole version, although more complicated to build, is slightly better. More surface area – more signal capture is a familiar rule. See it here: http: //w 7 hd. ddns. info/sats/building-a-twinlead-lindenblad. pdf 2

BUILDING A LINDENBLAD What is a Lindenblad? It is a circularly-polarized antenna with an omnidirectional pattern. Gain is about 9 d. B 3

Lindenblads installed at FAA control tower in Merced, CA 4

WHAT IT TAKES A simple parts list with inexpensive parts Typically under $30 to buy new parts Simple hand tools PVC construction for low cost Paint to overcome weather effects (Arizona sun is hard on PVC pipe otherwise) Can use 3/4” PVC Schedule 40 pipe The restriction is the length of the L brackets used for mounting the dipole elements. A 1 -1/2” L bracket will need an additional hole drilled. 5

CALCULATIONS Using 3/4” PVC pipe and tee, you will see these characteristics: 1 -5/16” O. D. At 432 MHz 1” I. D. 5/8” insertion depth 1/2ƛ =13 -5/8” 1/4ƛ 6 -13/16” 1/3ƛ 9. 1126” So the parasitic elements need to be 13 -5/8” length and 4. 556” from center. So 4. 556”-. 625” insertion = 3. 931” from the end of the ferrule. The parasitic elements should be 1/3ƛ apart. So the driven elements need to 6 -13/16”. The coax will be centered on the tee, so allow 1 -1/2” of shield and center conductor for going around the tee. This may actually form part of the dipole. 6

CALCULATIONS Free space dipole lengths 1/2ƛ 5905/F 432 13. 6689” 1/3ƛ 3936/F 1/4ƛ 2952/F 9. 11266” 6. 83449” 3/4” PVC insertion depth = 0. 625” 7

Parts List One 10 foot 3/4” PVC schedule 40 pipe 4 feet of #6 copper or aluminum wire cut to 13 -5/8 for 432 1 foot length of thin-wall 1/2” aluminum pipe. 6 -13/16 bottom element, 6 -13/16 for top element 4 L-brackets (1 -1/2 x 1 -1/2”) (1”x 1” are better) 10 feet of RG-6 or RG-8 X cable for portable installation (or longer if you plan on putting it up high). Note that using RG-6 will increase the resonant frequency over RG-8 X. Misc nuts and bolts Ferrite bead for cable 8

PARTS PICTORIAL All of the parts that have to be cut to length. (old photo) 9

70 CM CHARACTERISTICS Right-hand circular polarization Relatively light weight Easy to construct Horizon-to-horizon copy One dipole with 4 parasitic elements RG-6 coax for low loss (a dipole is actually 75 ohms) – up to 50 feet has been tested RG-8 X okay for less than 20 -foot runs 10

70 cm EZ Lindenblad. This is a working version I used to make a contact on SO-50. 11

My homebrew twin-lead 70 cm Lindenblad 12

ASSEMBLY SEQUENCE [1] Cut the parts to size for 432 MHz: _ 4 ea 5” PVC ferrules _ 1 ea top driven element 6 -13/16” _ 1 ea bottom driven element 6 -13/16” _ 4 each #6 wire cut to 13 -5/8” [2] Next you will insert the parasitic elements into the ferrules and insert the 4 ferrules into the PVC cross. 13

ASSEMBLY SEQUENCE [3] Measure 4 -1/4” from the end of ferrule and mark as a reference point for the parasitic element. [4] Drill a 5/16” hole for the element. You will use the wood screws to hold the element in place. [5] Do insert the parasitic elements at this time. Then align them for 30° angle from horizontal. 14

ASSEMBLY SEQUENCE [6] Make sure all 4 elements are at the proper 30° angle. [7] Tap the ferrules to insert them fully. [8] Now mount the elements using L brackets. You will drill two 5/16” holes through the tee and each element, then insert the 2” screws. Try to get the elements to be vertical from the tee. [9] Next, you will attach the coax with the shield connected to the bottom element, and the center conductor to the top element. [10] Add the ferrite bead aligned with the bottom of the bottom element. 15

ASSEMBLY SEQUENCE This is how I attached my RG-8 X coax. Note the positioning of the L brackets at right angles for top and bottom. The ferrules are not inserted in this photo for clarity. 16

ASSEMBLY SEQUENCE This is how it should look with the ferrules, parasitic elements, tee, and top and bottom elements assembled. 17

TIME TO PAINT At this point, you will want paint the antenna. Take care NOT to cover the mounting hardware – I wrap them with tape before painting. Whether you paint the parasitic elements depends on your preference – they hold up well without it. The PVC parts DO need to be painted for U/V protection and protection from weathering, especially in Arizona. We get plenty of U/V, lots of wind, sandstorms, and even very occasional rain. If you hear the term Haboob, that is what the weather guys call the sandstorms. You may also wish to insert caps at the end of the ferrules. That is why I made them longer – to allow for end caps to eliminate wind whistle. 18

TESTING PHASE Now it's time to test it out. The desired goal is to get a resonance point with less than 2. 5: 1 at about 435 MHz. 19

MOUNTING TIME Now you will mount the antenna in its desired location. If you have to use a extender to make the cable long enough, you will experience a small amount of loss. Keep in mind that each additional length of cable will add more loss. If you make both a 70 cm and 2 M Lindenblad, whether you will need a diplexer will depend on your rig. Several factors influence what you will need. Rig is simplex; a simple tee for the two antennas will work. Rig is duplex with single VHF/UHF input; a diplexer is needed. Rig is duplex with separate inputs for VHF and UHF; no diplexer is needed. 20

ENJOYMENT TIME Okay, time to work satellites using your new antenna. I use a program called Gpredict to plan out satellite passes. It has the advantage of being very accurate. You can also manually add satellites. Gpredict versions are available for Linux, Windows, and Mac. It provides a listing of pass information, frequencies to use, and a polar plot to see the pass. Current easy-to-work FM satellites are SO-50 and Fox-1 A (AO 85). Easiest SSB satellite to work is FO-29. You should also be able to hear Funcube-1 (AO-73), and possibly work it depending on conditions. 21

GPREDICT. 22

My website http: //w 7 hd. ddns. info contains a large amount of information for the amateur radio operator. Our club website is maintained by Bob AF 9 W http: //tucsonhamradio. org ENJOY – Ron W 7 HD w 7 hd. [email protected] com The End 23