System perspective from valve plate to antenna feed point

Introduction

The recent article Mullard QY4-400 (4-400) x 2 Class C AM plate and screen walked through design of a valve PA for a given power supply, power out etc, arriving at the required resonant load impedance.

This article walks through the design of transmitter pi coupler output, and antenna system (feed line + antenna).

Above is the result from Calculate initial load line of valve RF amplifier.

It is popular today to design the transmitter for a nominal 50+j0Ω load, then use an ‘ATU’ to transform the antenna system load to the transmitter, but in earlier days before VSWR meters were so popular, the pi coupler would simply be adjusted to achieve the desired operating point and power output. This article follows the latter path. Continue reading System perspective from valve plate to antenna feed point

1:49 EFHW transformer using a Jaycar LO1238 core – measurement with antenna

This article presents measurements of an EFHW antenna system using the transformer design worked up at 1:49 EFHW transformer using a Jaycar LO1238 core – design workup and bench measurements at 1:49 EFHW transformer using a Jaycar LO1238 core – measurement of losses.

The antenna system

Let’s take a system view, component views including bench measurements as reference above are important in qualifying components (eg acceptable Loss), but at the end of the day, the system view is very important. Whilst this section gives a VSWR perspective, it does that in the context of qualified system components.

In this article the antenna system comprises 11m of RG58A/U cable, the transformer described above and 20m of ‘radiator’ wire. This configuration should have a fundamental resonance around 7MHz and support harmonic operation at around 14, 21, and 28MHz.

Note that these type of antenna systems exhibit some amount of inharmonicity, ie the higher modes are not exact integer multiples of the fundamental resonance, there are contributions from both the ‘radiator’ wire, ‘counterpoise’ system and transformer.

Above is the VSWR plot looking into 11m of RG58A/U cable. The VSWR at the transformer jack point will be marginally higher, but this plot is typical of what might be presented to a transceiver. Continue reading 1:49 EFHW transformer using a Jaycar LO1238 core – measurement with antenna

1:49 EFHW transformer using a Jaycar LO1238 core – measurement of losses

Introduction

This article presents a review of a EFHW transformer using a Jaycar LO1238 core, a pack of 2 for $8 at Jaycar stores (Australia). The LO1238 is a 35x21x13mm Toroid of L15 material (µi=1500). Boxed up, it is probably safely capable of about 5W continuous dissipation.

The design is described at 1:49 EFHW transformer using a Jaycar LO1238 core – design workup.

Implementation

Above is the internals of VK4MQ’s balun. I would not use the pink PTFE tape, the balun core is extremely low conductivity and it is doubtful the tape helps. Continue reading 1:49 EFHW transformer using a Jaycar LO1238 core – measurement of losses

1:49 EFHW transformer using a Jaycar LO1238 core – design workup

Introduction

There are several articles on this site describing EFHW transformers using the Jaycar LO1238 toroid, two particularly relevant ones are:

This article presents a design workup of a EFHW transformer using a Jaycar LO1238 core, a pack of 2 for $8 at Jaycar stores (Australia). The LO1238 is a 35x21x13mm Toroid of L15 material (µi=1500). Boxed up, it is probably safely capable of about 5W continuous dissipation.

I will use the meanings explained at On insertion loss.

The design was developed in a SimNEC model which models a EFHW transformer, and can be calibrated against measurements of implementations. This helps evolve the model and develop some experience for likely values for leakage inductance etc. Continue reading 1:49 EFHW transformer using a Jaycar LO1238 core – design workup

Wooly thinking superposes power on transmission lines

Recently on social media, F6AWN cited a “document written by a team of engineers working in a company of 12,000 people devoting to perfecting power” which ended with the following formula:

The paper does not state that the phasors are RMS, RMS phasors, but it appears so… so let’s use like. Continue reading Wooly thinking superposes power on transmission lines

Mullard QY4-400 (4-400) x 2 Class C AM plate and screen

Valve datasheets often give one to few suggested sets of operating parameters for a valve in one several modes, and designers are left to sort of interpolate or extrapolate to their own set of parameters, eg loaded power supply voltage.

This article is a walk through and comparison of RF Power Amplifier Tube Performance Computer applied to the subject scenario.

Let’s extract from the Mullard datasheet.

We will use the Va=3kV scenario for this comparison. Continue reading Mullard QY4-400 (4-400) x 2 Class C AM plate and screen

4:1 voltage balun vs 1:1 current balun on the MFJ-949E @ 1.8MHz

A question of often asked is whether the ‘best’ balun on a T match ATU is:

  1. a Ruthroff 4:1 voltage balun (as it often fitted internally);
  2. a Guanella 1:1 current balun; or
  3. a Guanella 4:1 current balun.

The subtext of the question is often that the OM has switched from (a) to (b) in pursuit of improved common mode current rejection, and found they cannot match their existing antenna which matches ‘just fine’ using the (a).

This article explores (a) and (b) using a configuration similar to the popular MFJ-949E @ 1.8MHz, and comments on (c).

Let’s declare that although the MFJ-949E is specified for 1.8MHz, it is disadvantaged… which will exaggerate the problem to some extent… but in so doing make the problem easier to see.

We will use a SimNEC model of the ATU and a purely resistive load, as large as the ATU will match. The Smith charts shown are normalised to Zref=400+j0Ω as it is a better context for visualising loads on 400Ω transmission line typical of the use with two wire lines.

1. The bare MFJ-949E T match to a coax output jack

Above is the model. The coloured squares a sample points in a sweep of values of the matching components C1, L1, and C2. Green is loss less than 3dB, Yellow 3-6dB, and red greater than 3dB. Continue reading 4:1 voltage balun vs 1:1 current balun on the MFJ-949E @ 1.8MHz

Evaluation of Aliexpress sourced EBM315 battery packs (for DB3DL2)

In Repack of Hikoki / Hitachi EBM315 battery pack (DB3DL2) I discussed the repack of a battery pack. At the same time I also ordered a no-name replacement 1.5Ah battery on Aliexpress for $25 incl shipping… with some reservation as most batteries I have purchased on Aliexpress have failed to deliver half of the rated capacity.

So, the battery arrived and I tested it, the purple trace above, and I was pleased to see that it exceeded the rated capacity a little.

So, I purchased another from the same seller, and it duly arrived, and to my surprise, it exceeded rated capacity by 30%.

Both batteries recharge properly on the Hitachi / Hikoki charger.

Time will tell whether they are good value. In any event, they use screws to hold the cap on so they can probably be repacked with good cells.

My ATU is soooo good, it will give a perfect match on anything, even…

I was reading the mail on a net on 40m one day many years ago, and one of the participants asked people for their recommendation on his intended ATU purchase. This was pretty technical for this net where the qualification to join is that you tell all what you are going to have for dinner.

So, one of the guys tells ’em “mine will tune the proverbial wet string.”

Gotta do better than that? Next guy says “mine is so good… I tuned up the other day for a perfect match then thought the band was a bit dead until I realised I did not have an antenna connected!”

Let’s work a real example

MFJ claimed that the MFJ-949E is the most popular tuner purchased… so lets use it as an example.

We will use 160m as I measured the magnetising impedance of the internal balun a few days ago and used in the a recent article. This article uses the same basic model… but no antenna connected.

Above is the test setup, NanoVNA connected to the transmitter jack, mode switch set to Tuned / Balanced… and there is no antenna on the balanced line terminals (the balun link is in place). Continue reading My ATU is soooo good, it will give a perfect match on anything, even…

Lewallyn’s meaning of Radiation Resistance

Hams tend to not share a common meaning for terms, and in defence will say that anything is ok so long as the author makes their meaning clear. The latter is a huge burden in online discussions where a post may be less than 50 words.

Tom Rauch states:

Radiation resistance is both the most useful and the least useful antenna-related term. Radiation resistance can easily be misused and rendered useless. This is because radiation resistance has multiple poorly-defined meanings. When a term has several nebulous meanings or uses, it is only natural that misuse or mixing of terms appear. Lack of a firm, single, well-accepted, definition allows the term “radiation resistance” to slip from one definition into another. This often results in well-intentioned, but totally erroneous conclusions, that seem to follow accurate, logical, thought!

Continue reading Lewallyn’s meaning of Radiation Resistance