**Next message:**duane: "Re: Power-Line Noise Eliminated"**Previous message:**L. B. Cebik: "re:Autek RF-1 batteries"**In reply to:**JEVERHART@cayman.vf.mmc.com: "Re: T2FD, etc."**Messages sorted by:**[ date ] [ thread ] [ subject ] [ author ]

Joe,

You are correct. The antennas with resistive components to swamp out SWR

are very much less efficient than vitually any "normal" antenna. It does

not matter whether the arrangement is a folded dipole with a resistor near

300 ohms or a standard dipole with a resistor near 50 ohms. The amount of

power that is radiated will be proportional to the ratio of the swamping

resistor and the impedance that the antenna sees at a given frequency

without the resistor in accord with standard parallel impedance

calculations. This applies equally to incoming and outgoing signals.

The losses will vary with the impedance of the antenna, which will differ

on each band (apart from the swamping resistor). Where power is of little

concern, as in military applications, the losses are not too significant.

However, for QRP work, the losses can be very significant (depending upon

one's circumstances). If you have a natural impedance of 50 ohms and a

swamping resistor in this vicinity, then you will get a net 25 ohm

impedance, a 2:1 SWR, and one have of your power converted to heat. THat

is a 3 dB loss, like cutting your power from 2 watts to 1 watt, and

received signals will be half an S-unit down. That is livable. However,

consider antenna impedances of a feww hundred ohms in parallel with a 50

ohm resistor and calculate how much power is heat and how much signals may

be down. The degree of difference, of course, can only be determined if

you can also have an unswamped antenna of similar proportions side-by-side

for the comparison. Like so many other cases, the antenna may seem fine

if no comparison is possible.

For most (but probably not all) QRP situations, a dipole with parallel

feeders and an ATU is likely to be more efficient as an all band

antenna--and likely cheaper in the long run.

-73-

LB, W4RNL

**Next message:**duane: "Re: Power-Line Noise Eliminated"**Previous message:**L. B. Cebik: "re:Autek RF-1 batteries"**In reply to:**JEVERHART@cayman.vf.mmc.com: "Re: T2FD, etc."**Messages sorted by:**[ date ] [ thread ] [ subject ] [ author ]

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