This article describes a Guanella 1:1 current balun which has high common mode impedance (Zcm) and low Insertion VSWR. It is for application on antennas that have low VSWR(50) on at least some bands, especially if they would be used without an ATU on some bands.
The purpose of the balun is to minimise common mode feed line current which may contribute to EMC problems when transmitting, and contribute to increased ambient noise when receiving. Reduction of feed line common mode current also helps in achievement of expected load impedance characteristic, radiation pattern and gain. This article gives measured Zcm, but the definitive test of the effectiveness of such a balun is direct measurement of common mode current Icm… and it is so easy.
Example applications are half wave centre fed dipoles, fan dipoles, trapped dipoles, G5RV with hybrid feed, ZS6BKW, trapped verticals, monopoles, ground planes.
To obtain low Insertion VSWR, the choke will be wound with 50Ω coax, to demonstrate the practicality of the design budget (but good quality) regular (ie solid PE dielectric) RG58C/U will be used. Foam dielectric is NOT recommended. Solid PTFE coax could be used, but avoid coax with steel cored inner conductor, it may be lossier than you think at low frequencies with the silver cladding is relatively thin.
The candidate core is the readily available FT240-43 (Fair-rite 2643803802, 5943003801), it is a low cost NiZn ferrite with medium µr, and its µr and loss characteristic contributes to a broad high impedance choke well suited to this application.
Above is a model of the expected Zcm with 11 turns of RG58C/U coax and an equivalent shunt capacitance of 4.6pF. Continue reading A low Insertion VSWR high Zcm Guanella 1:1 balun for HF
My article G3LNP balun explored the operation of the G3LNP 4:1 balun on a 200Ω asymmetric load and found it exhibited extreme Insertion VSWR on what should have been an ideal impedance transformation but for the asymmetric element.
The balun is in fact a Voltage Balun and cannot be expected to work properly on asymmetric loads.
A correspondent proposes that the balun probably works very well on a nearly symmetric load such as a half wave dipole.
There are two aspectes to this proposition:
- the assumption that a common half wave dipole implementation is nearly symmetric; and
- the balun works well on a nearly symmetric load.
Continue reading G3LNP balun with symmetric ‘matched’ load
G3LNP described a 4:1 balun for HF antennas in Radcom Nov 2017.
Above is the schematic supplied by G3LNP. He describes the dashed link at the bottom as optional, but uses it in his prototype so this analysis is with that link installed. The prototype used equal lengths of coax (1m PF100, an RG-6 like coax), and the toroidal choke appears to be 8t on a T130-2 powdered iron core.
Exploration of behaviour of baluns on extreme asymmetric load often reveals whether they work properly for asymmetric loads.
Continue reading G3LNP balun
Review: magnetic stirrer with heating plate and digital display XB 85-2 documented problems that prevented the device being very useful.
Attempts to tune the supplied PID controller above were frustrated by a lack of meaningful documentation supplied or found in searches on the ‘net, and the fact that the display is sometimes faked to appear that the temperature has stabilised. With any non-zero I term, it behaved badly and some observations suggest that it suffers from integral windup. It is truly a piece of Chinese junk and unusable.
Above is an independent logger capture of the temperature from switch on. There is a large overshoot, and then, no matter what the settings, it oscillates and the lowest amplitude obtained was 1°pp (above). The overshoot is almost as much as observed in manual warm up when power is cut at 40°. Continue reading Fixes #1: magnetic stirrer with heating plate and digital display XB 85-2
We have had wired broadband service delivered to these premises for almost ten years, supplied by three vendors: Telstra Bigpond, iiNet, and Amaysim.
Amaysim has supplied a 25Mb/s broadband service for a month now and set an important baseline for service.
Above is a plot of the 90 percentile and 10 percentiles for each week so far. Continue reading First full month of Amaysim broadband broadband Internet access
I recently had need to attach four wires to a set of pads on a device for programming its microcontroller. The pads for these sort of things are often on difficult to solve pitch, this one is 2mm which is not too bad.
Above is the target and solution.
The target is the four vias right next to the LEDs on the daughter module. Continue reading A little programming adapter for 4 x 2mm pitch pads
This article shows just how easy it is to make an inexpensive low VSWR load for antenna analyser validation / measurements.
Above is an AA-600 sweep of the prototype from 10kHz to 100MHz. VSWR reads 1.02 in ‘All’ mode at 100MHz… better than the inherent accuracy of the instrument.
It is made from two 100Ω 1% 1206 SM resistors purchased on eBay for about $2/100, so about $0.04 for the resistors, and 40mm of bare copper wire (0.5mm phone / data wire in this case).
In use, it is held in contact with the coax socket (in this case an N type) with a pair of disposable plastic first aid tweezers (yep, you can buy them on ebay for about $0.20/pair).
While you are at it, make a good short circuit termination by scrunching up a bit of (clean) kitchen aluminium foil and press that against the coax socket conductors.
Try both of these on your antenna analyser and see how it stacks up.
DL4YHF published a frequency counter design based on the PIC16F628.
The design has been modified by many, copied by even more, and usually without attribution.
This article documents one of these copies (TB-244756 printed under the chip footprint), a $6 kit off eBay which comes with no documentation, though the screen mask is enough to correctly place components.
It turns out to be DL4YHF’s “DISPLAY_VARIANT 2”, the variation is that it uses a common cathode display.
Above the built kit with the 7550 voltage regulator replaced with a 78L05. Continue reading DL4YHF 50MHz counter on a Chinese TB-244746 PCB
A recent online posting asserted that an antenna is optimal when itself resonant, and fed with a resonant feed line length so delivering a purely resistive load to a source, and further that implementors needed to be careful that a shorter dipole could be offset to some extent by a longer feed line but it would be inferior because:
no short antenna is more efficient than a resonant-length antenna
… but does that stand scrutiny?
An NEC experiment
Lets walk though an experiment using NEC-4.2 models of a dipole of 2mm copper wire at 10m height at 7.1MHz over average ground (σ=0.005, εr=13).
- source has a Thevenin equivalent source impedance of 50+j0Ω;
- feed line is lossless.
The results are sensitive to the model assumptions.
We will calculate the ratio of radiated power to the power delivered by the transmitter to a matched load, let us call it TransmitEfficiency for the purposes of this article. Continue reading “No short antenna is more efficient than a resonant-length antenna”
This article documents a small experiment with a quite small untuned loop, and LNA and receiver on 80m to assess its ability to copy signals on the band as well as the station transceiver on large antenna.
A significant factor at 80m is that ambient noise is quite high. Let’s consult ITU P.372-12 for guidance.
Curve E is the median city noise, at 3.6MHz Fa is about 62dB. At a more detailed level, P.372-12 gives the median noise figure for Rural precincts at 51.8dB and that figure is more appropriate to the test location (large block rural residential).
The test was carried in a few spots, at 50-100 m from the main station dipole. Continue reading Small untuned loop with MMIC LNA on 80m