DG7YBN / 403 MHz / GTV RS-19m
  Last Update Dec. 31th 2014


.......



Performance Data and Geometry
Pattern and VSWR
Download Area
Mounting long vpol Yagis
Bill of Materials / Shopping List
Stacking


GTV RS-19m   Yagi with bent DE for reception of  Radio Sondes


This Yagi is designed to give Radio Sonde Hunters a very clean pattern, high performance Long Yagi with the necessary
bandwidth for monitoring the 402 - 404 MHz core part of the Radio Sonde band. It is 50 ohms direct feed, the coax cable
can be connected as is. A ferrite core added on the fed line is welcome but not essential.

This design is derived using the GTV 70-19m 432 MHz Low Noise Yagi as baseline.

Now with full building plan (Download Area) including the 'Blade DE' as introduced in Dubus 4/2014


Current distribution



Performance Data
 

                       402 MHz        403 MHz       404 MHZ
Gain vs. isotr. Rad.  17.8 dBi       17.8 dBi      17.8 dBi
Gain vs. Dipole       15.5 dBD       15.6 dBD      15.6 dBD
-3 dB E-plane                        25.0 deg.
-3 dB H-plane                        26.0 deg.
F/B                  -34.6 dB       -30.9 dB      -28.1 dB
F/R                  -29.1 dB       -29.1 dB      -28.1 dB   
Impedance                              50 ohms
Mechan. Length                       4413 mm
Electr. Length                       5.93 λ

Stacking Dist. h-pol.
top-to-bottom                        1.65 m or 5.4 ft
side-by-side                         1.72 m or 5.6 ft

Geometry

Element Diameter = 1/4 in = 6.35 mm, DE = 3/8 in = 9.525 mm (Update: 8 mm ele., see down the page)

Runnig an SWR plot with EZNEC Auto Segmentation (11 to 8 segm.) results in 405.5 MHz.
Applying the SBC factor of 1.02 mm/MHz tells us that the SBC to be added to the BC must be
(404.7 - 403.2) MHz x 1.02 mm/MHz = 1.53 mm


Boom Correction for mounting elements on boom with standard plastic insulators

Segmentation BC and Base BC (see below) must be added.



Remember - this is UHF. Cut elements very precisely. Use a large calliper gauge if you can get one. Make a mark
for final length, saw about 0,5 mm in front of the mark and grind down to final measure. Below you find BC numbers for
other boom dimension 

Data for 1/4" = 6.35mm elements:

             Tube dim.          BC            SBC          BC+SBC
Boom        20 x 20 mm        7.1 mm    +   1.53 mm   =    8.63 mm
Boom        25 x 25 mm       10.4 mm    +   1.53 mm   =   11.93 mm
Boom         1 x 1  in       10.7 mm    +   1.53 mm   =   12.23 mm

Elements on-boom-with-standard-insualators cutting table (corr. 2014.11.27) 

        Pos.      Full Length   Full Length    |   Pos.       Full Length      Full Length      Full Length
                   in NEC      on 20x20 Boom   |                in NEC        on 20x20 Boom     on 25x25 Boom
                               (7.1 + 1.5 mm)  |                              (7.1 + 1.4 mm)   (10.4 + 1.4 mm)
Refl.      0.0      356.5           365.1      |      0.0        355.0           363.5            366.8
DE(b)     97.0     97-343.0         351.6      |     97.0      96.5-342.0        350.5            353.8
DE(a)    112.0      0-97             96.0      |    112.0        0-96.5           95.5             95.5
D1       163.5      336.0           344.6      |    164.0        332.5           341.0            344.3
D2       264.0      330.5           339.1      |    264.0        327.0´          335.5            336.8
D3       459.0      319.0           327.6      |    459.0        314.5           323.0            326.3
D4       687.5      312.5           321.1      |    687.5        308.3           316.8            320.1
D5       952.0      308.0           316.6      |    952.0        304.0           312.5            315.8
D6      1235.0      306.0           314.6      |   1235.0        301.0           309.5            312.8
D7      1528.5      302.0           310.6      |   1528.5        296.3           304.8            308.1
D8      1830.5      296.0           304.6      |   1830.0        292.0           300.5            303.8
D9      2136.0      295.0           303.6      |   2136.0        290.0           298.5            301.8
D10     2434.5      294.0           302.6      |   2434.5        287.5           296.0            299.3
D11     2729.0      292.0           300.6      |   2728.5        286.5           295.0            298.3
D12     3021.5      291.0           299.6      |   3021.5        285.5           294.0            297.3
D13     3302.5      290.0           298.6      |   3302.5        283.0           291.5            294.8
D14     3585.5      288.5           297.1      |   3585.5        283.0           291.5            294.8
D15     3868.5      286.5           295.1      |   3868.5        279.0           287.5            290.8
D16     4163.5      282.0           290.6      |   4163.5        276.5           285.0            288.3
D17     4413.0      280.0           288.6      |   4413.0        272.5           281.0            284.3
       ele. 1/4"   ele. 1/4"      ele. 1/4"    |  ele. 8mm     ele. 8 mm       ele. 8 mm        ele. 8 mm


(*) Note: element lengths for Ø 8 mm fit 5/16" too

The Drivers diameter is 3/8" for 1/4" elem. and 10 mm for 8 mm elem. design.
Use EZNEC's Auto-Segmentation at 1050 MHz.

SBC 8 mm model: the 8 mm models f_res at given high segmentation is 403.1 MHz.
At conservative auto segmentation on 403 MHz it lands in at 404.5 MHz
Delta is 1.4 MHz with a factor of 1.02 mm/MHz this results in 1.448 extra mm.

Element through boom - with numbers derived using SM5BSZ's BC.exe applied

Ready to saw and drill" data for mounting elements on boom with standard insulators on 20 x 20 mm boom including a 30 mm offset from boom ends:
Insulators Ø_outer = 6 mm, Ø_inner = 4 mm press fit, booms wall thickness = 2 mm



SBC 4 mm: (404.3 MHz - 403.1 MHz) x 1.02 mm/MHz = 1.224 mm plus 0.7 mm on top to compensate insulators influence
makes a total of 1.224 + 0.7 mm = 1.924 mm

The Drivers diameter is 10 mm for the 4 mm elem. design.
Use EZNEC's Auto-Segmentation at 1050 MHz.

Find a technical drawing of this Yagis boom and strut in the Download section

Advanced feeding & symmetrising

Placing a ferrite an the feeding coax as close a possible to the dipole connection will do for any reception purpose
However - here is an advanced methode:
A simple symmetrising member may be made from a 3 x 1/4 Lambda line grounded at the far side with
N-flange-bushing and an aluminium plate and ferrite added as close as possible to the DE, see below.







Pattern and VSWR Plots

Elevation and Azimuth plot at 432.1 MHz (horizontally polarised - for vertical polarisation swap views)

 

SWR plots - inner band and full band

   

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Downloads - file update 2014-11-29

EZNEC file of this Yagi with 4 mm elements  

EZNEC file of this Yagi with 1/4" elements    

EZNEC file of this Yagi with 8 mm elements  

Drawing of boom of this Yagi in 2 sections     

Drawing of boom of this Yagi in 3 sections     



Drawing of this Yagis 'Blade' Dipole in 2 mm aluminium sheet metal  








Mounting a long vertically polarised Yagi

An ordinary boom strut may be used to produce a fixed distance to the pole. Which ideally should be a fiberglass
one. With help of a traverse and V-shaped kevlar, aramid or polyester guy ropes one can avoid boom sag
and add additional stability as now the supporting structure becomes 3 dimensional.

Place strut ends and guy rope fastenings as far away from elements as possible.








Bill of Materials

On-Boom-Builds

Element mounts

18 pcs: insulator 25 mm square boom (WiMo #23042.25)
18 pcs: stainless screw M3 x 40 for 25 mm boom (or 45) mm
18 pcs: M3 washers, large (Ø 9.1 mm)
18 pcs: M3 washers, ordinary (Ø 7 mm)
18 pcs: M3 self locking nut

Quarter Wave Line

1   pc: RG - 142 B/U, 400 mm (trimm to resonate at 403 MHz as 3 x 1/4 λ, approx. 373 mm)
1   pc: N-cable-flange-bushing

Boom Connnector

1 (2) pcs: Boom connector 25x25 mm boom (WiMo #23033)
2 (4) pcs: screw M6 x 35
2 (4) pcs: nut M6
4 (8) pcs: M6 washer

Other

6 pcs: Screw M3 x 8
4 pcs: M3 washers, ordinary (Ø 7 mm)
4 pcs: M3 nuts

... will be continued








Stacking


    For Stacking Pattern Data and Plots on the GTV RS-19m => see GTV 70-19m








Symmetrising 50 to 50 ohms Feedline

The principle is similar to the 1/4 Lambda coax. Adding 2 x 1/4 Lambda or a half wave line does not change anything but allows
to form a gentle bow below the boom or until behind the Reflector. Follow practical construction hints on "Building a Yagi" page.

    Attenzione!     Take care when lengthening the coax, measure the right length instead of refering to given v-factors only.
    A good choice may be the diam. 5 mm PTFE coax RG-142 B/U: real resonate length (403 Mhz as 3/4 Lambda) shield-shield
    is around 373 mm.



    Find more information  about getting the coax stub right on my Phasing & Matching Lines page








73, Hartmut, DG7YBN


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