On testing two wire line loss with an analyser / VNA – part 3

This article series shows how to measure matched line loss (MLL) of a section of two wire line using an analyser or VNA. The examples use the nanoVNA, a low end inexpensive VNA, but the technique is equally applicable to a good vector based antenna analyser of sufficient accuracy (and that can save s1p files).

On testing two wire line loss with an analyser / VNA – part 1

This article series shows a method for estimating matched line loss (MLL) of a section of two wire line based on physical measurements (Duffy 2011).

Above is a short piece of the line to be estimated. It is nominal 300Ω windowed TV ribbon. It has copper conductors, 7/0.25, spaced 7.5mm. The dielectric is assumed to be polyethylene… but later measurements suggest is has slightly higher loss than polyethylene. The test section length is 4.07m. Continue reading On testing two wire line loss with an analyser / VNA – part 3

On testing two wire line loss with an analyser / VNA – part 2

This article series shows how to measure matched line loss (MLL) of a section of two wire line using an analyser or VNA. The examples use the nanoVNA, a low end inexpensive VNA, but the technique is equally applicable to a good vector based antenna analyser of sufficient accuracy (and that can save s1p files).

On testing two wire line loss with an analyser / VNA – part 1

Above is a short piece of the line to be measured. It is nominal 300Ω windowed TV ribbon. It has copper conductors, 7/0.25, spaced 7.5mm. The dielectric is assumed to be polyethylene… but later measurements suggest is has slightly higher loss than polyethylene. The test section length is 4.07m. Continue reading On testing two wire line loss with an analyser / VNA – part 2

On testing two wire line loss with an analyser / VNA – part 1

This article series shows how to measure matched line loss (MLL) of a section of two wire line using an analyser or VNA. The examples use the nanoVNA, a low end inexpensive VNA, but the technique is equally applicable to a good vector based antenna analyser of sufficient accuracy.

Above is a short piece of the line to be measured. It is nominal 300Ω windowed TV ribbon. It has copper conductors, 7/0.25, spaced 7.5mm, though as can be seen the spacing is not perfectly uniform. The dielectric is assumed to be polyethylene… but later measurements suggest is has slightly higher loss than polyethylene. The test section length is 4.07m. Continue reading On testing two wire line loss with an analyser / VNA – part 1

Do I ‘need’ a masthead preamp to work satellites on 2m? – G/T vs G/Ta

A reader of Do I ‘need’ a masthead preamp to work satellites on 2m? – space noise scenario has written to say he does not like my comments on the hammy adaptation of G/T.

Above is an archived extract of a spreadsheet that was very popular in the ham community, both with antenna designers and sellers and end users (buyers / constructors). It shows a column entitled G/T which is actually the hammy calculation. The meaning possibly derives from (Bertelsmeier 1987), he used G/Ta.

Ta is commonly interpreted by hams to be Temperature – antenna. It is true that antennas have an intrinsic equivalent noise temperature, it relates to their loss and physical temperature and is typically a very small number. But as Bertelsmeier uses it, it is Temperature – ambient (or external), and that is how it is used in this article.

Let’s calculate the G/Ta statistic for the three scenarios in Do I ‘need’ a masthead preamp to work satellites on 2m? – space noise scenario.

Base scenario

Above is a calculation of the base scenario, G/T=-29.74dB/K.

Also shown in this screenshot is G/Ta=-23.98dB/K. Continue reading Do I ‘need’ a masthead preamp to work satellites on 2m? – G/T vs G/Ta

QEX on SWR dependence on output impedance #2

(Wright 2021) sets  out to prove a dependence of VSWR on source impedance, a common ham assertion.

Wright gives the schematic of the minimal VSWR detector he simulates in SPICE.

The schematic is sparse, it does not show where the forward and reflected signals are measured. Continue reading QEX on SWR dependence on output impedance #2

QEX on SWR dependence on output impedance

(Wright 2021) sets  out to prove a dependence of VSWR on source impedance, a common ham assertion.

Wright gives the schematic of the minimal VSWR detector he simulates in SPICE.

The schematic is sparse, it does not show where the forward and reflected signals are measured. Continue reading QEX on SWR dependence on output impedance

Measurement of one of those ham lore components – figure 8 twinline

A long time ago when I first ‘got on the air’, a mentor suggested I build the famous figure 8 dipole (or zip line dipole in North America). The advice was that it had characteristic impedance very close to 70Ω, ideally suited to a half wave dipole and could be made with a clever not obviating the need for a centre insulator. A ham rite of passage?

Above, the dipole from the ARRL Antenna Book. Continue reading Measurement of one of those ham lore components – figure 8 twinline

Do I ‘need’ a masthead preamp to work satellites on 2m? – terrestrial noise scenario

Do I ‘need’ a masthead preamp to work satellites on 2m? – space noise explored a scenario for a high gain antenna pointed skywards. This article explores the case of a omni antenna which basically captures ‘terrestrial’ noise.

Base scenario is a low end satellite ground station:

  • 144MHz;
  • terrestrial noise (satellite with omni antenna);
  • IC-9700, assume NF=4.8dB;
  • omni antenna;
  • 10m of LMR-400.

Continue reading Do I ‘need’ a masthead preamp to work satellites on 2m? – terrestrial noise scenario

Do I ‘need’ a masthead preamp to work satellites on 2m? – space noise scenario

A question asked online recently provides an interesting and common case to explore.

Base scenario is a low end satellite ground station:

  • 144MHz;
  • satellite;
  • IC-9700, assume NF=4.8dB;
  • high gain (narrow beamwidth antenna);
  • 10m of LMR-400.

Continue reading Do I ‘need’ a masthead preamp to work satellites on 2m? – space noise scenario

MFJ-261 – review of review

A recent review of the MFJ-261 (Bogard 2021) was interesting.

 

From MFJ’s web site listing:

Connects directly to the transmitter with PL-259 connector. No patch cable used, reduces SWR. Finned aluminum, air-cooled heatsink. Handles 100 Watts peak, 15 Watts average. 50 Ohms. Covers DC to 500 MHz with less than 1.15:1 SWR. 1 ⅝” round by 3″ long.

That is pretty stunning for a device with a UHF connector, more on that later. Continue reading MFJ-261 – review of review