# Turning 1kW into QRP

Effective Isotropically Radiated Power (EIRP) is one means of comparing the performance of a transmitting station.

An inefficient antenna can lead to very low EIRP, perhaps surprisingly low. Consider these four examples at 3.6MHz,

The following NEC-4.2 models give some insight.

## QW vertical with 120 buried radials

Considered by so many experts to be the benchmark for a grounded monopole, here is a quarter wave vertical with 120 buried radials.

Above, 120 buried radials: GAIN=-1.8dBi, radiation efficiency=20.7%.

At 1kW RF input, EIRP=661W.

## QW vertical with 32 buried radials

Above, 32 buried radials: GAIN=-1.9dBi, radiation efficiency=20.3%.

At 1kW RF input, EIRP=646W.

(Now if you are paying attention, you might be wondering about this 120 radials rule.)

## QW vertical with 4 buried radials

Above, 4 buried radials: GAIN=-3.1dBi, radiation efficiency=15.3%.

At 1kW RF input, EIRP=490W.

## OCF short vertical dipole for HF

Using the assumptions and model at OCF short vertical dipole for HF.

Above, OCF short dipole: GAIN=-21.0dBi, radiation efficiency=0.272%.

At 1kW RF input, EIRP=7.9W. Since this analysis did not capture ATU and feed line loss, this figure could be optimistic.

## Conclusions

The full size quarter wave monopole with 120 buried radials is held to be the benchmark omni by so many experts, though unachievable for most suburban residential plots. In this analysis, with a 1kW transmitter and ignoring feed line loss (which should be very low), EIRP is 661W.

The full size quarter wave monopole with 32 buried radials is about the upper limit of what hams can accommodate in a large yard, probably the upper practical limit of performance achievable from an omni directional antenna on 80m other than in a large antenna farm. In this analysis, with a 1kW transmitter and ignoring feed line loss (which should be very low), EIRP is 646W.

A full size quarter wave with just 4 radials performs a little poorer, EIRP would be 490W.

The OCF short vertical dipole for HF is a considerable compromise with GAIN=-21dBi, EIRP is just 7.9W… into the QPR category with a 1kW transmitter.

If you were using the common 100W radio, divide all the above EIRP figures by 10… so at the lower end, the OCF short vertical dipole for HF would have EIRP of just 0.79W… that is QRPP from a 100W transmitter.