DL7APV

128yagi on 432MHz, Why?

I started 432MHz EME in Berlin, 1983 with 4x21el. F9FT. After the wall came down I was able to buy

farmland outside Berlin with enough space for all future crazy ideas. I started there with 8x21el. F9FT, later

8x13wl 9BV design was set up and then 16x13wl 9BV. I thought I had a great antenna. But the mechanical

structure was not strong enough and the booms 20x20x2 (later 25x25x2) were far too small for 9.2m long

antennas. So once the 16 yagis were ready in 2008 I immediately started to think about a stronger antenna.

As often happens in life a 'happy accident' helped to bring the idea closer to reality. One of my neighbours

found big rotating assembly with ball bearing from a T174 GDR backhoe on eBay. We organised the

transport to my QTH and a few days later it was stored in my barn.

The picture shows the rotating assembly with 1.6m diameter & about 500kg weight with lots of rust. After

sandblasting, adding lot of grease and some paint it was like new.

But next decision was WHICH antenna should be

mounted? Before deciding that, the mast height was

defined as 5m, to allow for a 10m dish as well as other

possibilities (and support when getting older).

Before the antennas can be calculated the foundation had to be made. I assumed 10 tonnes of concrete

would be sufficient. On top of the foundation comes the weight (3.1 tonnes) of the whole construction.

Again with help from my neighbours and some heavy machinery this was finished by a morning. A farmer’s

concrete mixer (1m³) and the steam shovel did a good job.

The rotating assembly was placed in position by a crane, then adjusted until it was under 0.2° out of balance,

the ball bearing was like new, and it was so free that even my wife Astrid could turn it by hand!

Then the decision WHICH ANTENNA had to be made? There are only 2 possibilities: Dish or yagi?

Pro Dish Pro Yagi array

Many bands possible Lower wind-load at same gain

Easy polarity rotation No permission needed

Low losses between feed and preamp Open feed lines can have also low losses

Can grow slowly

Nobody tried such a big array

Only NC1I has 48 yagis and so the performance of a larger array is unknown, so from a technical perspective

it was a challenge. Next decision was which yagi would be the best fit for such an array? To save feed lines

the first idea was to use long boom yagi. But the horizontal boom for elevation would be very heavy and first

simulations showed some influence of the support structure on the antenna pattern. Even a 9m long yagi

with a stacking distance of more than 2m showed pattern deformation due of the structure which I had

assumed would be 50x50cm (in reality this became 70x75cm). The only solution was to use foremast

mounted antennas. The maximum practical length of such a yagi without support booms is around 3m.

Others such as KL7WE have tried this approach in the past. With a height of 5m and width of Nx6m the

maximum possible size for the support structure was 10x18m. Any bigger would not be tolerated by the

neighbours.

With these restrictions 128 yagis with an as yet undetermined number of elements was the only practical

solution. After careful consideration, numerous calculations and simulations the GTV-70-11w by DG7YBN

was selected. This antennas produces an optimal G/T for the boomlength and is unaffected by rain due to its

wideband design. Longer antennas would be understacked and even though the first lobe would be lower

the overall G/T is worse.

Single 11el. YBN dry (above) and wet (below) 427-437 MHz

Figure 1 Single GTV 70-11w VSWR measured when dry

Figure 2: Single GTV 70-11w VSWR measured when wet

The main structure was welded at home and the horizontal boom for elevation was obtained from local

supplier of flat conveyor belt systems. This was the single most expensive part in the entire system. The

horizontal boom dimensions are 70x75cm and 18m long and comprises of 3 x 6m parts. The main structure

was fabricated from steel square section tube section 80x80mm and 100x100mm.

Figure 3: Vertical support with 1 boom

Figure 4: Closer inspection of the elevation rotator with chain drive fitted

The gears for the

elevation system were

taken from a fertilizer

spreader, already in stock

and therefore cheap! The

main gear wheel was

made from stainless steel

in an apprentice

workshop for 1kg of

coffee. The 2nd gear

wheel is held in a block

which takes all the axial

forces to relieve the next

worm gear. The motor is

from a cable winch for a

jeep, 12V.

The horizontal rotor includes the original drive gear, the same worm gear as used in the elevation system as

well as a 12V motor.

Figure 5 the main axis with gear wheel and gear rim

The outer two horizontal booms were mounted using a crane, and then some FM DX antennas were

mounted above the array. FM DX is great with an antenna of only 10° beam width.

The 60x5mm tubes were slotted at the end to

receive the 48x4 extender tubes and fixed with 2

screws. No backlash!

The total tube mast length is 8,5m and for the eight

FM DX antennas 9m. There is no degradation in

pattern due to the upper 8 FM antennas.

US digital encoders for vertical & horizontal, both encapsulated

firstly in a metal box to protect from RF and then plastic for

weatherproofing.

The dipole bending machine saved a lot of time, my brother in law helped with the 128 dipoles.

The bench shears were invaluable when cutting the 1280 Elements to within +1…2mm which were then

hand filed to +/-0.2mm (I needed several long winter evenings with many glasses of red wine). The 35cm

sliding Vernier calliper was mandatory!

The 20x20x2 6m (standard

supplied length) booms were

cut in two and then the holes

were marked and drilled in

the barn.

After press fitting 2560 shoulder washers and adjusting 1280 elements the barn was used as storage for the

partially completed antennas.

Next task was to pre-stretch the 4mm diameter insulated copper wire from the roll to make the feed lines.

40m lengths were installed between two towers and in the middle we pulled with a rope as hard as we

could. The end result was perfectly straight feed lines. The pre-stretched feed lines were then cut to length,

stripped in the middle and at the ends and then put into the bending jig. Finally the crimp type sockets and

PTFE spacers were added.

Next was to solder the dipoles in correct position, any wrong 180° turn would cause big problems later on.

Soldering to the dipoles was no problem, the dipole had mounting holes. The Copper dipoles were all

painted with a waterproof lacquer later on.

The joints to the combine to next feed line need some mechanical help in the form of crimp-type sockets.

Some additional details, every 2nd tube has another tube in parallel at the opposite face of the horizontal

main boom. These tubes are also fitted with a mast clamp. This adds a lot of stiffness to the array and

prevents individual antennas from twisting in the wind.

At 45° elevation there is less than 6cm of sag in the tubes over 8m

The booms of the antennas were extended so that the antenna boom is either connected to the 2nd tube

with another mast clamp or to a support structure. This gives excellent stability even at high wind speeds.

The aluminium feed lines needed extra support. The support was fabricated using PTFE spacers clamped to

the support boom.

A 4-bay sample array was SWR tested and optimized with the copper feed lines. All the aluminium feed lines

were calculated and tested when the array was complete. Previous tests have shown that the length is not

very critical. A velocity factor is 0.98 or 0.96 is not significant because the transformation is very wide band.

This was be proven when the final array was tested. The VSWR is <1.2 with a simple slug tuner made from 4

rolls of PTFE which were clamped over the ends of the feed line close to the sleeve balun.

The sun noise Azimuth plot shows a little asymmetry, but I also observed this on the old system. Maybe this

is a problem caused by the central balun as the feed lines are exactly the same length. The vertical diagram is

as expected.

More info on my homepage and on DG7YBNs page

Results

DL7APV comparison of new and old

system Old 16x13wl DJ9BV design

New 128x11el.DG7YBN

design

Antenna length 13wl / 9,2m 3wl/2m

Number of antennas 16 (4x4) 128 (8x16)

Stack hor./vert. 2,16m / 1,97m 1,20m / 1,09m

Gain 29,7 dBD 33,7dBD (+/-0,3)

Pointing Accuracy +/-5° at windy wx,

not usable above force 5

H: 0,35° backlash, V no

backlash

Tested at 120km/h

beamwidth H/V 4° / 4° 1,8° / 3,8°

Losses Dipole – preamp, total 0,2 dB 0,32 dB

6mm Aluminium open feed lines 200 Ohms

4mm copper feed lines 200Ohms 10m 0,1 dB

12m 0,12dB

1,2m 0,022dB

Relais/relay HF4000 7/16 0,02 dB 0,02dB

Balun & 3 Adapter 0,08 dB 0,13dB

Antenna temperature 50K 26K

1rst preamp DJ3FI 0,35dB NF /20dB 0,25 NF / 24dB

2nd preamp 0,4dB NF (micomm) 0,6dB / 20dB PGA103

both preamps together 0,31dB NF 43dB Gain 0,26dB NF 43dB Gain

RX path 100m aircom+

Filter + preamp in shack

abt. 10dB

NF<2dB

abt. 10dB

NF<2dB

TX R&S SSPAs 750W at feed 750W at feed

TX line under ground

Cable around rotor

45m 1 5/8" 0,7dB

6m ecoflex15 : 0,4dB

PA-Wattmeter 0,3dB Total 1,4dB

55m 1 5/8" 0,7dB

10m ecoflex15 : 0,7dB

PA-Wattmeter 0,3dB Total 1,7dB

TRX Drake TR7 + DB6NT Transverter

(unchanged last 10years)

Tracking manual F1EHN system

Read outs US Digital ENCODER US Digital ENCODER

Measured values:

sun noise at F=70 (F=28@432) 18 dB when antenna was new, at

the end 17dB with bended booms 21.7 dB!

Echoes CW at 5W in JT at 0,5W CW at 200mW / JT 100mW

Smallest station worked MX0CNS 2el. & 60W We will see!!

Fun factor Very high Much higher now!!!!

Used material: All in mm All in m Total weight / kg

Steel:

18m horizontal arm 750

Big ball bearing 500

Double T beam 120x120x12 21.4 440

Square tube section 80x80x4 31,3 292

Square tube section 100x100x6 25,6 427

=2409

ALU Round pipe 60x5 159 385

Round pipe 48x3 76 87

Square tube section 20x20x2 384 154

Square tube section 20x20x1 18 10

Square tube section 18x18x1 124 25

Round pipe 6x1 223,6 10

=671

Copper Round pipe 6x1 89,6 18

CuL wire 4 224 28

=46

=3126kg!

Other material qty

PTFE Spacer 3mm for CuL feed line 384m

PTFE Spacer 3mm for alu. feed line 158m

Cross clamps 60 to 60mm 42pc

Cross clamps 60 to hor. Main boom 6pc

Cross clamps 60mm tube to 20mm boom 220pc

CuPal washer to connect copper to aluminium without corrosion

66pc

Plastic nipple for element fixing 2560pc

Dipole holder made of PP 128pc

crimp-type socket 192pc

MS tube 40x0,5 1

Rope 3mm 300m

Epoxy glue

MANY screws, nuts, spring washers all stainless steel M3 to M16 up to 12.9 stability! And the dozens of screws and nuts (mostly M3) which slipped through my fingers and are in the grass / Soil now forever.

Big thankyou to Hartmut, DG7YBN who helped with material/Ideas and lots of simulations; DL7SI, DL7ZN,

DL7ON, DL7AIG, DJ3FI, my neighbours and of course my XYL Astrid who always supports my crazy ideas.

73 Bernd DL7APV@gmx.de / www.DL7APV.de