Netcom 9th ASC Antenna Course

7/31/2019 Netcom 9th ASC Antenna Course

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G3/TE/09JAN04/JKS/HFTNG

NETCOM/9th Army Signal Command


Coverage Desired (< 30km,30-300 km, long-haul)

Selected Mode of Propagation

Directional orOmnidirectional

Polarization

Availability of good grounds

Ease of camouflage

Space availability (clear ofobstructions?)


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Ideal solution depends onwhether antenna is balancedor unbalanced in design

Use coax for unbalanced

designs (one side grounded)Use open-wire line forbalanced antennas (ideal) ORcoaxial cable with a balun(balanced-unbalancedtransformer) (best) or by

winding a coaxial choke toprevent ground currents

Use an appropriate cable forthe power level and loss(length)

7-8 turns, approx 10 ft of cable


7/39G3/TE/09JAN04/JKS/HFTNG

NETCOM/9th Army Signal CommandNETCOM/9th Army Signal Command

Feedline Loss (Matched)

0

0.5

1

1.5

2

2.5

0 10 20 30 40

Frequency, MHz

Loss,

dB/100ft.

Belden 9913

RG-8

RG-58




Ratio of the voltage of the reflected wave at any onepoint on the feedline to the voltage of the forwardwave at that same point.

Ideal SWR (Matched line) is 1:1

The higher the SWR, the more power is lost in thefeedline and more power reflected back intotransmitter finals

Many radios reduce power automatically at 2:1 or 3:1SWR to save final transistors from overheating(automatic fold-back)




20516900.7 dB10.1 dB65:128.4

15636300.4 dB5.2 dB18:124.9

23067570.8 dB9.8 dB73:121.1

20737800.6 dB9.0 dB65:118.1

18635300.5 dB1.9 dB6:114.1

28699670.9 dB10.4 dB134:110.1

19649810.3 dB5.8 dB49:17.1

318811810.9 dB5.7 dB63:13.8

7640164012.1 dB25.9 dB1818:11.8

MaxVoltage450

MaxVoltageRG-8A

Loss, 100ft450 Line

Loss 100 ftRG-8A

SWRRG-8A Coax

MHz




Frequency range: 2 to 30 MHz

Polarization: Horizontal andvertical simultaneously

Power capability: 1,000 watts(CHECK MOUNTING PLATE

some are limited to 50 wattsby the baluns!)

Radiation pattern - NVIS

Azimuthal (bearing):Omnidirectional




Ubiquitous in the mobileenvironment

Majority of energy is radiatedabout 45 degrees to the

horizonPattern strongly affected byvehicle body

Good grounding is critical

OK for ground wave comms

over short distances (< 30km)16/32 ft transportable unitswith ground radials (AT-1011/U)

Requires tuner




Figure A-15. Radiation pattern of a whip antenna.


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Less gain than a dipole, butonly requires one support

Combination of vertical andhorizontal radiation


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At least 1/2 in length,preferably 2 or more

Longer wire, lower takeoffangle, more gain

To make it directional, add a600 resistor (rated at halfthe xmit power)

Works best with a 12:1 balunif using coaxial cable feedline


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Ground wave and short-rangeskywave

Omnidirectional

Quite adaptable with existingtuners and 35-40 ft verticalheight


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Medium- to long-rangeskywave propagation

Antenna should be at least 1in length, 2 or more better

To make directional, add 600resistors on each leg.


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45 to 500-foot wire (longer isbetter)

Poor performer at shortlengths

Can be terminated withresistor for improved tuningand directivity


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Medium- to long-rangeskywave

500 to 1000 ft lengths of greatvalue

Can be terminated fordirectivity


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Feedline3 x 100 ft. RG-8X coaxial cable w/N-M connectors

2 F-F N adapters

Adapters 2 ea. Of N-N Female, N-Female to UHF Male, BNC-Male toN Female

Lightning/NEMP Protector w/N Female connectors (Polyphaser orHber-Suhner)

Grounding

1 inch copper braid strap, 10 ft w/lugs (PRC-150 ground)1 inch copper braid strap, 6 ft w/lugs (amplifier ground)

Ground rod kit

MK-2551 Surface Wire Grounding Kit


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Netcom 9th ASC Antenna Course