At Ferrite cored RF chokes in Class-E RF power amplifiers a design was offered for a choke using a Fair-rite 2843000202 core (commonly sold as a BN43-202), and the point was made that some products sold as BN43-202 might be significantly different.
Let’s look at the calibrated model estimates of choke impedance and core loss, side by side. Continue reading Ferrite cored RF chokes in Class-E RF power amplifiers – core material issues
Last update: 19th April, 2022, 1:44 PM
Class-E RF power amplifiers have become quite fashionable in ham radio in the last decade or two.
This article discusses a common issue with the design of the RF choke providing DC to the Class-E stage.
Above is a circuit above is from (Sokal 2001) which explains the amplifier and gives guidance on selection of components. One key recommendation is that the
usual choice of XL1 being 30 or more times the unadjusted value of XC1. This spells out that L1’s role is essentially an RF choke, it is intended to pass DC but to largely prevent RF current, it needs a high impedance at RF, and low DC resistance. Continue reading Ferrite cored RF chokes in Class-E RF power amplifiers
Last update: 25th July, 2022, 1:19 PM
I recall the arrival of the Swan 500CX in Australia, it was regarded highly and talked up quite forcibly on air by the local agent.
At the time, I was still acquiring the knowledge and skills to analyse the PA design in the 500CX, but I recall lots of on air discussions that were disparaging, but were not convincing.
More recently, I have had occasion to perform a desk study of the 500CX PA.
The Swan 500CX used a pair of 6LQ6, low cost TV sweep valves. From the GE datasheet, the valves are rated at 30 W plate (anode) dissipation. No safe grid 1 current or dissipation is given, so the safe approach is to regard that they must be operated with zero grid current, Class AB1 in this case. Continue reading A desk study of the Swan 500CX PA
Last update: 12th March, 2022, 9:16 AM
A common scheme for narrow band match of an end fed high Z antenna gives a Simsmith model for the matching arrangement that follows.
The tapped coil could also be considered an autotransformer.
Continue reading A common scheme for narrow band match of an end fed high Z antenna – further explanation
Last update: 27th January, 2022, 7:01 PM
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
Last update: 8th September, 2021, 7:45 AM
A reader of A common scheme for narrow band match of an end fed high Z antenna commented:
…if the coil is tapped at 1/3, surely then the coil is a 1:3^2 or 1:9 transformer and the capacitor simply ‘tunes out’ the coil reactance, what is the input impedance when it has a 450+j0Ω load?
That is very easy to calculate in the existing Simsmith model.
Above, with load of 450+j0Ω, the input impedance at 50MHz is 8.78+j34.36Ω (VSWR(50)=8.4), nothing like 50+j0Ω. Continue reading A common scheme for narrow band match of an end fed high Z antenna – surely it is a 1:9 transformer?
Last update: 29th June, 2021, 2:01 PM
This article discusses the kind of matching network in the following figure.
A common variant shows no capacitor… but for most loads, the capacitance is essential to its operation, even if it is incidental to the inductor or as often the case, supplied by the mounting arrangement of a vertical radiator tube to the mast. Continue reading A common scheme for narrow band match of an end fed high Z antenna
Last update: 26th January, 2022, 10:15 AM
This article outlines a Simsmith model developed to explore / confirm behavior of some linear Class B push-pull HF broadband power amplifiers.
The design is for a system power output of about 80W on a 24V supply, it is a combination that should work with practical system components with good efficiency.
Above is a first step, an estimate of an initial load line for the PA. The calculator is written in valve terms, but is quite applicable to this scenario. Continue reading A simple generic Simsmith model of a linear push-pull Class B broadband HF power amplifier
Last update: 11th June, 2021, 7:42 AM
One of the very important designs of HF broadband MOSFET power amplifiers was that of Helge Granberg in Motorola application note EB104.
This article offers an explanation of how the the alternative output circuit at Fig 5 of EB104 works.
Let’s look at the schematic diagram of the PA.
Above is the schematic from EB104, of interest for this article is the output circuit comprising T2 and T3 which are intended ideally to provide a drain to drain load of 50/9=5.55Ω. Continue reading EB104 alternative output circuit
Last update: 25th May, 2021, 10:05 AM
This article is on in a series of a desk review, a pre-purchase study if you like, of the MiniPa100 kit widely sold on eBay and elsewhere online.
The above pic from an eBay advertisement of the 2020 version of the PA would suggest very strongly that there are three turns on the secondary of the output transformer, and a half turn on each drain. Interestingly the 70W versions also appear to use three turns, alarm bells ring!
Here is a little table that shows the maximum power obtainable with a transformer of this type for various supply voltages and secondary turns. Continue reading A desk review of the MiniPa100 kit – #2: transformer T2 turns ratio
Last update: 11th June, 2021, 7:42 AM