PA: TX chain PA to Antenna

@2014/7/12

before math the PA output to Antenna, must have a antenna first.

A Pair of Ugly Helical antenna

normal Helical short antenna is popular for handy transceiver. it's efficiency is poor, especially at HF and no good ground plane. there are several program can design the rubber ducky antenna.

Helical design program: ( DOS program, very detailed information)

http://www.smeter.net/antennas/short-helical.php

Air helical calculator include the self resonant frequency:

http://hamwaves.com/antennas/inductance.html

Helical whip antenna calculator: (windows program)

http://www.vk4adc.com/web/index.php/hf-projects/45-hf-antennas/102-hf-helical-whip-calc

Both these calculator assume use air core, and practically, you might use some plastic as coil form, like PVC, PP-R which cheap and can found everywhere.

I make 2 of them, on use PVC, and another use an unknown plastic material as coil form. The mainly problem is the turns calculated is seems too many than it actually needed, i check the resonant frequency use by a sweep generator and AD8307 detector.

the thin one diameter 8mm plus 0.4mm wire diameter, 50CM, calculation result is about 300 Turns to resonant at 27.5Mhz, but i found only 150 Turn is needed. 2 possible reason, first one, the PVC/unknown material magnetic permeability is far bigger than 1, second one is the turn space is too massy, maybe both.

A better way to make such antenna might like this: choose the proper length and wire diameter, make it almost tight wound, so eliminate the turns space problem.

practical performance review:

condition:

transmitter: PA: TX chain smoking Design + big one Antenna [ NO any match circuit ]
Receiver: ICOM-91A HT
environment: full of building, transmitter in the room, close to window.

result:

use ICOM-91A carried rubber antenna, transmission distance about 100 meter long
even in room, some conner signal strength is significantly reduced.
use self made rubber, resonant at 27.5Mhz. transmission distance rached to 200meter - 300meter. in room, no dead conner.
put the AD8307 detector 2 metres away from the transmitter, use a VHF rubber antenna, signal strength is -60dBm. use self made helical antenna, signal strength is about -50dBm. almost 10 times better than random receiver antenna.
the obvious pitfall is no ground plane, or counterpoise.