Category: Amateur Radio

Ambient noise measurement using whip on vehicle – #2 – active antenna electronics

This article continues from Ambient noise measurement using whip on vehicle – #1 – estimate Antenna Factor with a case study for the active antenna electronics.

For this discussion, I will use the amplifier developed at A high performance active antenna for the high frequency band, but applied to the antenna described at Ambient noise measurement using whip on vehicle – #1 – estimate Antenna Factor.

Let’s assume that the antenna + amplifier will be used with a HF receiver with Noise Figure 6dB, Teq=864.5K.

From (Martinsen 2018) Fig 3.8, the amplifier internal noise at the output terminals is -118dBm in 100kHz @ 3.5MHz. That implies that the amplifier Noise Temperature is 857.93K. The amplifier has 6.4dB voltage gain which needs to be subtracted from the AF calculated for unity gain (at the amplifier input terminals). Continue reading Ambient noise measurement using whip on vehicle – #2 – active antenna electronics

Last update: 21st January, 2022, 7:38 AM

Ambient noise measurement using whip on vehicle – #1 – estimate Antenna Factor

This article lays out a method for estimating the Antenna Factor of a short vertical mounted on the roof of a vehicle for use with a high impedance amplifier for ambient noise measurement at 3.5MHz.

Ambient noise is commonly dominated by man made noise, and it often arrives equally from all directions. For measurement of such noise, the captured power depends on average antenna gain, and so the calculations below focus on gain averaged over the hemisphere.

Antenna Factor is often very convenient for field strength measurement as it relates the external E field strength to the receiver terminal voltage given a certain antenna (system). In fact, given a short vertical terminated by a high impedance amplifier, Antenna Factor is often fairly independent of frequency over several octaves of frequency. Continue reading Ambient noise measurement using whip on vehicle – #1 – estimate Antenna Factor

Last update: 19th January, 2022, 8:11 AM

Loop in ground (LiG) for rx only on low HF – #10 SND comparison with LoG

The Loop in Ground project is about a receive only antenna for low HF, but usable from MF to HF. The objective is an antenna of that is small, low profile, and can be located outside the zone where evanescent modes dominate around noise current carrying conductors, like house wiring to minimise noise pickup.

To some extent, the project was inspired by KK5JY’s Loop on Ground (LoG).

This article presents a comparison of Signal to Noise Degradation metric (see Signal to noise degradation (SND) concept) for both antennas, the common elements being: Continue reading Loop in ground (LiG) for rx only on low HF – #10 SND comparison with LoG

Last update: 12th January, 2022, 8:40 AM

A mid life kicker for the 2500VA 230V 50Hz genset

About 10 years ago I purchased a 2500VA genset on eBay for about $250 incl delivery. It turned out to have wiring problems behind the control panel, and required an hour’s work to fit some new wires and terminations and make it safe. The seller refunded $80 as compensation.

It has what appears to be a genuine Honda GX160. Now I bought it with I must say a great deal of skepticism, but having worked on many Chondas (Chinese Honda ‘clones’) this is undoubtedly a class above, and I think on all the evidence available, it was a Chinese manufactured Honda destined for the domestic market. Continue reading A mid life kicker for the 2500VA 230V 50Hz genset

Last update: 7th August, 2022, 3:29 PM

Choosing a ferrite mix for a 160m unun rationally

One often sees people ask for help in choosing a ferrite mix for a particular application. A recent thread on social media asks for help designing a unun for the 1.8MHz amateur band, and it has provided the opportunity for participation, even if the content was not good.

An important early step in designing a ferrite cored transformer is to find a combination of ferrite material, core geometry, and number of turns to deliver acceptable core loss at the lowest desired frequency.

Design of a transformer to cover just the 1.8MHz ham band is a relatively simple exercise. Continue reading Choosing a ferrite mix for a 160m unun rationally

Last update: 9th January, 2022, 3:37 PM

Loop in ground (LiG) for rx only on low HF – #8 measurement and observation

This article was revised 03/01/2021 to correct an error: the NEC-5.0 model reported was actually the KK5JY LoG, fixed, apologies.

The Loop in Ground project is about a receive only antenna for low HF, but usable from MF to HF. The objective is an antenna of that is small, low profile, and can be located outside the zone where evanescent modes dominate around noise current carrying conductors, like house wiring to minimise noise pickup.

The antenna comprises a square loop of 3m sides of 2mm bare copper wire, buried 20mm in the soil.

This article reports measurement of feed point impedance and a ‘calibrated’ NEC-5.0 model. Continue reading Loop in ground (LiG) for rx only on low HF – #8 measurement and observation

Last update: 3rd January, 2022, 6:58 PM

Resolve measurement of I1, I2 and I12 into Ic and Id

This article explains the technique used at

Introduction

If we consider a two wire transmission line, we can define currents I1 and I2 flowing in the same direction in each conductor. Continue reading Resolve measurement of I1, I2 and I12 into Ic and Id

Last update: 3rd January, 2022, 5:48 AM

No-name video baluns common mode impedance

I purchased a bunch of no-name, no-spec, video baluns on eBay for use with radio antennas at MF and low HF. A pair of these are for transporting 75 ohm coax video signals over twisted pair LAN cable.

Above, the two styles of baluns purchased. Given the label, nondescript as it is, there is quite a possibility that the internals are the same. Continue reading No-name video baluns common mode impedance

Last update: 19th December, 2021, 12:46 PM

Matching a centre loaded 80m vertical – a shunt match tutorial

This article describes a method of measurement and adjustment using an antenna analyser or VNA to quickly set up a shunt match, a narrow band match (ie for one band, or even only part of the band).

The article uses Rigexpert’s Antscope as the measurement / analysis application, the techniques will work with other good application software.

To demonstrate the technique for matching such an antenna, let’s use NEC-4.2 to create 80m feed point impedance data for a 12m high vertical with 8 buried radials (100mm) and centre loading coil resonating the antenna in the 80m band for simulation of measurement data.

An s1p file was exported from 4NEC2 for import into Antscope, to simulate measurement of an example real antenna.

Analysing the ‘measured’ data

Step 1

Above is the VSWR curve displayed in Antscope. Note that the actual response is dependent on soil types, antenna length and loading etc, but this is a good example for discussion. It is not real bad, another example might be better or worse. Continue reading Matching a centre loaded 80m vertical – a shunt match tutorial

Last update: 20th December, 2021, 11:13 AM