Category: Amateur Radio

This article is a follow on from Receive only antenna for 160m – matching and performance discussion. It develops a SimNEC model that imports the loop impedance, and transforms it with an ideal transformer to quickly find an optimal transformer ratio and predict system losses.

Results are for the scenarios calculated and may not be extensible to different scenarios.

Another caveat: I have reservations about transmission line modelling in SimNEC, especially for composite conductors, but for the purposes of the discussion, assume that it is reasonably correct.

Above is the SimNEC model, it assumes reciprocity of the antenna system. Continue reading Receive only antenna for 160m – matching and performance discussion – improved SimNEC model

A reader of Receive only antenna for 160m – matching and performance discussion referred me to an online discussion with a simpler solution.

A couple of quotes from posters…

It almost doesn’t matter what the actual receiver Zin is. What matters is the 100ft of 50 or 75 Ohm coax that is used to get the Rx-only antenna signal from where the antenna is placed to the receiver.

and…

That’s what I thought, also.

A few hundred feet of coax can be ~8000 pF of parallel capacitance which should short out signals by having only about 11 Ohms of reactance.

So the gist of this is that:

• receiver Zin does not matter;
• the 100′ of coax or 300′ of coax matters; and
• 300′ of coax can be adequately represented by a shunt capacitance of 8000pF.

Receiver input impedance is not necessarily a tightly controlled parameter, but it is measurable, so lets take a real example.

IC7300 example

Let’s measure Zin of an example IC7300 around the 160m band.

Above is Zin plotted from a saved .s1p file. At 1.85MHz, Zin=56.2-j5.4Ω, a little off nominal, but pretty close (VSWR50=1.35). The dotted line is X and the dashed line is R, ignore the solid line… it is for people who don’t understand impedance. Continue reading Receive only antenna for 160m – matching and performance discussion – 8000pF?

This article explores the design / analysis of a passive receive only antenna for the 160m band (1.8MHz).

The example and calculations assume linear systems, if there is significant nonlinearity that gives rise to significant IMD, IMD noise is not captured by the analysis.

Results are for the scenarios calculated and may not be extensible to different scenarios.

Another caveat: I have reservations about transmission line modelling in SimNEC, especially for composite conductors, but for the purposes of the discussion, assume that it is reasonably correct.

The example antenna is a K6SE 14’x29′ Pennant optimised for 160m.

Design objective

The objective here is to design a receive only antenna system that can be relatively remote from local noise sources (like house wiring), and captures enough external signal and noise that the receiver internal noise does not degrade S/N too much. Continue reading Receive only antenna for 160m – matching and performance discussion