Propagation and Antennas Net Frequency Selection

Antenna Contest Cook-Off

Tony FuscoAFE3TM/AFA3TF

Illustrations from open internet sources

Some MARS Tales? “RC” always works. A low antenna is good for NVIS. Verticals make good DX antennas. Your tuner tunes your dipole. A feed-line can be any length. Low SWR indicates a good antenna. The propagation is going long.

What’s going on up there?

How do you know?

Millstone Hill Digisnode

The numbers that matter most foF2 F2 layer Critical Frequency, MC (FOT <10-15%) foF1 F1 layer Critical Frequency, MC (FOT <10-15%) foE E layer critical frequency, MHz fmin Lowest frequency at which at which echoes are

received MUF(D) Maximum Usable Frequency for D=3000 km C-level Confidence level: 11=very good, 22=good, 33=

moderate, 44=questionable, 55=bad D 100 200 400 600 800 1000 1500 3000

(km)MUF-AM 4.5 4.5 4.7 5.1 5.6 6.3 8.4 13.9 (mc)MUF-PM 7.8 7.8 8.2 8.7 9.4 10.5 13.7 21.8 (mc)

When selected net frequency is below the Critical Frequency (foF)

When selected net frequency is above the Critical Frequency (foF)

This is what happens when we operate our station above the foF (FOT)

SSN Graph

Net Frequency & Propagation Lets go to our VOACAP crystal ball to see how

critical frequency and antenna selection can affect our nets.

J0G VM HD RC “ “ RB “ “ RA “ “ Note: VOACAP area plots represent 10% of

month days. Actual conditions will be much worse for the 90%.

Ant & Prop Summary

Station Examination: Where do I go from here? Am I ready for the Solar Minimums? Money, time and space constraints?

“Space” the last frontier!

A dipole is a dipole until it meets mother earth!EZ-NEC - a 65 ft dipole for gain and impedance

7.30 mc Gain 2.04 dbi / 73.4 ohms J 0 - ½ wl 3.65 mc Gain 1.60 dbi / 13.5 ohms -J 1K - ¼ wl 1.82 mc Gain 1.12 dbi / 3.4 ohms -J 2K - 1/8

wl 0.91 mc Gain .09 dbi / 1.1 ohms -J 5K - 1/16

wl

But bring it back to Earth! The same dipole at 26 ft over ground gives us: - 7.3 mc gain +6.08 dbi / 71.2 ohms REZ

- 0.91 mc gain -9.32 dbi / 1.6 ohms –J

5.3K

Now elevate it to the same <1/4 wl (220’) gives us:

- 0.91 mc gain is now +5.24 dbi !

“Its not the size of your dipole but where you hang it!”

Feeding your Antenna See Jun QST

Details 40 meter dipole feed-line heat loss @14mc with 100’ feeds, tuner and 1500w

* 600 ohm ladder line loss = 175w * 450 ohm window line loss = 541w * RG-213 coax loss= 1376w! Magic tips for mismatched feed lines:

- ¼ wave - transforms antenna impedance - ½ wave - reflects antenna impedance.

“Only when both ends of a transmission line

terminate in its characteristic impedance is the system is happy!”

What can we expect from our antennas?Lets look at 8 antennas in the perfect EZ-

NEC world.

GMV - 35 & 50 ohm PMV - 50 ohm Dipoles - at ¼ & ½ wave hi Inverted Vs – at ¼ & ½ wave hi V Dipole - at ½ wave hi

Caution Tag Line - using HF verticals

GMV 35 ohms on 2.5” lawn

GMV 35 ohms on 2.5” lawn

GMV 35 ohms on 2.5” lawn

GMV 50 ohms on 2.5” lawn

GMV 50 ohms on 2.5” lawn

GMV 50 ohms on 2.5” lawn

PMV 50 ohm

PMV 50 ohm

PMV 50 ohm SWR

Dipole at ¼ wave – 17 ft

Dipole at ¼ wave – 17 ft

Dipole at ¼ wave – 17 ft

Dipole at ½ wave - 35 ft

Dipole at ½ wave - 35 ft

Dipole at ½ wave - 35 ft

Inverted V Dipole ¼ wave high

Inverted V Dipole ¼ wave high

Inverted V Dipole ¼ wave high

Inverted V Dipole ½ wave high

Inverted V Dipole ½ wave high

Inverted V Dipole ½ wave high

V Dipole ½ wave high 35/23 ft

V Dipole ½ wave

V Dipole ½ wave high

Antenna cooking by the numbersTYPE GAIN dbi ANGLE deg IMP ohms

GMV 35 -.18 25 35

GMV 50 -1.24 27 50

PMV +.64 20 50

Dipole ¼ hi +5.79 65 78

Dipole ½ hi +7.3 25 69

Inv V ¼ hi +4.02 90 50

Inv V ½ hi +6.22 30 50

V Dipole ½ hi +5.71 35 50

Enough said about that!That was an antenna eye-full!If you have antenna questions – please see

me later!And now – what we’ve all been waiting for…

NED Antenna Cook-Off Seven members submitted ideas A few are real in use antennasMost are lets see - what ifs’- or old ideasThe review was objective, participants were

not part of the selection process.

Entry 1 – A Loop 140 ft sides @40 ft

Entry 2 - Inv V 40’ hi – 51’ sides

Entry 3 - RC/RB Dipole @ 18’ hi

Entry 4 - Fence Rider 102/5 FT

Entry 5 – Broadband Antenna 40’hi 400 ohm loads into 8 ft gnd rods

Ver2 with counterpoise on grass

Entry 6 the AS-2259 15 Ft hi

Entry 6/2nd – Sloped TFD 40’/6’hi

Entry 7 142’ Dipole 40’ high

Cooking our gain by the numbersENTRY RA RB RC J0G Total

Gain

#1 Loop 4.79/55 8.64/60 10.93/35 10.77/15 35.13

#2 Inv V 1.49/65 3.8/90 4.19/90 7.49/90 16.97

#3 Inv V NA 2.6/90 1.66/90 NA NA

#4 Fencer -11.14/90 -5.01/90 -2.09 .65/60 -17.59

#5 Broad 1

-12.36/90 -8.94/90 -14.82/45 -.68/25 -36.35

#5 Broad 2

-10.04/50 -8.48/90 -1.83/45 -.95/25 -21.2

#6 AS-2259

-8.28/90 -2.11/90 1.87/90 3.17/90 -5.35

#6 TFD -7.07/85 -.32/85 -.34/80 2.65/30 -5.08

#7 Dipole 6.04/90 6.78/90 7.99/45 9.21/25 30.03

Note: Gain/angle

dbi/deg

Igor the envelope please“All MARS” category antenna winner is the Grand Loop! AFA2DO – NY’s - Paul Conway “Trans Global” winner is – again – NY’s the Grand Loop!“Regional” winner is the Big Dipole! AFA3TF - PA’s – Me “Restricted Antenna by CC&R” winner is the Fence Rider! AFA2QD – NJ’s - Bob Harrision“Wet Noodle” Antenna award goes to the WB Worm

Warmers! AFA3PB – VA’s - Ken Heitner

Kudos to: AFA3WD - Dennis Welch, AFA3QP - Skip Masker, and AFA2PD - Paul Dukette . Dennis’s tuner fed Inv-V may actually be called the “most practical” of the bunch. A new category!

The Net Triad

FO

T A

NT

NET FREQ

Traffic Capability

Finally! Summary: What’s really important to MARS? Its “US” – its team and how we accomplish the

mission. Future shock is here – in time, I hope that all members can adapt to the new procedures to make our corner of the D0D/MARS Trans-Global Network a better place to connect and move traffic.

After my 16 months of observation…our critical task: - Generate/Move USMTF Traffic (can you?) - Air/Army Net Frequency Agility (can we?) - Mission Ready (are we?) BL: Take the Initiative and Practice, Practice,

Practice!