Random Antenna Bits

December 22, 2015

CWTD Episode #77

Portable Antennas
Excellent ways to get on the air while in the field … and at home!

Podcast

1)  Portable QRP Antennas

Portable hamming is a popular activity particularly during Spring, Summer and Fall

Different types dictate antenna used

– Short impromptu outings need quick up skywires

– Camping, SOTA and IOTA ops or events can be more elaborate

Types of portable antennas

    Random length wire

– Non-resonant wires thrown over convenient tree or ??

– Example is 24 to 30 foot wire and similar ground counterpoise

– Quick to put up/take down

– OK for casual operation

– Needs tuner

W1PID is great enthusiast … http://www.w1pid.com/>

– Somewhat unpredictable results

– Variant is EARCHI 6_40 antenna

http://earchi.org/92011endfedfiles/Endfed6_40.pdf

easy to duplicate, uses 30 ft wire and coax for counterpoise

 The End Fed Half Wave Antenna

– L(ft) = 468/F(MHz)

– Also works on harmonics

A number of proponents …

 Steve Yates AA5TB …http://www.aa5tb.com/efha.html>

N2CX Halfer … http://www.njqrp.org/n2cxantennas/halfer/index.html>

 

 

 

 

-Performance approaches center fed resonant dipole

-Requires tuner or matching device

 

Commercially available

 

Par EndFedZ …http://www.lnrprecision.com/endfedz/>

 

SOTAbeams …. http://www.sotabeams.co.uk/half-wave-end-fed-antennas/>

 

 

 

Vertical antennas

– Inefficient if too short

– Requires substantial ground system

– Commercially available

 

The Buddistik …http://www.buddipole.com/buddistick.html>

 

QRP Kits … http://www.qrpkits.com/pac12.html>

 

 

-Full size verticals are cumbersome for casual portable use

 

 Magnetic loops

 

-Convenient for limited space or crowded public areas

 

-Many SOTA ops like portability and band-hopping characteristics

 

-Common 3 foot loops

-Convenient size

-Fast, easy setup

-Mount on camera tripod

-Inefficient on 40 meters, good on 20 and higher

-Narrowband – needs retuning for QSY

 

-Commercially available from ham distributors

 

Alex Loop ...< http://www.alexloop.com/instructions2.html>

 

Alpha Antennas … http://www.alphaantenna.com/>

 

 

Dipoles and doublets

 

-Center fed half wave dipole

 

-Dependable, repeatable performance, particularly with balun

 

-Somewhat more effort than end fed wires

– but not much if inverted vee configuration

– Center at least 20 ft up, ends above head level

 

-Can be mulitbanded

-Leapfrog segmented dipole

-40/20/15 tri-bander

-Doublet uses open wire line for multibanding

 

Dipoles commercially available

SOTA BEAMS ... http://www.sotabeams.co.uk/antennas-hf/

 

 

“Fixed mobile” operation

 

-Use ordinary HF mobile antenna on vehicle

 

-Extra ground system helps effectiveness

 

-Good when no antenna supports

 

-Convenient for inclement weather

 

-Superb for spur of the moment operation

-While wife is shopping at the mall

-While vacationing and can’t set up portable station

 

N2CX mobile operations …

                 N2CX vehicle parked at Whitestone Brewing Company … not QRV after this stop!

 

 

               K400 mounted on edge-lip of rear hatch                           Ground wire brought to bolt to ensure solid ground to vehicle 

 

Is my antenna working?

  • Use Reverse Beacon Network to check it out www.reversebeacon.net
  • “Skimmers” monitor CW portions of ham bands
  • They log signals received and post on web page
  • The see CQ’s and TEST signals
  • E.g. “TEST TEST de N2CX N2CX K”
  • Screenshot from N2CX home antenna with 3W

 

  • Handy check but…

– Depends on propagation, antenna pattern, available skimmers, QRM

– Less than 10 dB SNR – weak signal

– 10 dB to 20 dB – reasonable signal

– Above 20 dB SNR – you’re golden!