At Yet another dodgy coax collinear I wrote about a design published recently in QST.
More recently, a ‘design’ has emerged in eHam forums that appears to be identical. Continue reading Yet another dodgy coax collinear II
Author: Owen
APRS trial Bowral – Wilton – Wollongong – Macquarie Pass – Bowral
I recently travelled to Wollongong and back by a round trip, partly to evaluate APRS coverage on the Picton Rd.
Above is a screenshot of the 140km track. Continue reading APRS trial Bowral – Wilton – Wollongong – Macquarie Pass – Bowral
An A/B comparison of a low G5RV with a MobileOne M40-1 – statistical analysis
This article reports statistical analysis of the measurements made for An A/B comparison of a low G5RV with a MobileOne M40-1 (read it first).
I left it for readers to visually form a view of the difference between the antennas, and the implications for credibility of folk lore about the two antenna types, this article addresses the quantitative difference between the average S/N ratio of the antennas.
Statistical analysis
Standard statistical techniques can be used to arrive at a difference in the mean S/N of the antennas and to quantify the uncertainty in that statistic. Continue reading An A/B comparison of a low G5RV with a MobileOne M40-1 – statistical analysis
NEC-4 vs NEC-2 on a low small transmitting loop
This article compares a series of models of a small transmitting loop at varying height above real ground using NEC-4 and NEC-2.
The models are of an octagonal loop of thin wire of the same area as a 1m diameter circle over real ground (0.007/17). Height is measured to the centre of the loop, and all impedances are wrt the main loop.
Above is the NEC-2 result.
Continue reading NEC-4 vs NEC-2 on a low small transmitting loop
An A/B comparison of a low G5RV with a MobileOne M40-1
This article reports measurements on 40m of S/N as a receiving station in Melbourne of a 10W transmitter switched between a G5RV and M40-1 over a 1 hour period.
The experiment compares the antenna over a specific, but very relevant ionspheric path so it is more useful than ground level measurements in a car park or playing field.
Above is a screenshot of the beacon signal switched between the two antennas. Continue reading An A/B comparison of a low G5RV with a MobileOne M40-1
Accuracy of estimation of radiation resistance of small transmitting loops
A simple formula exists for calculation of radiation resistance of a small transmitting loop in free space. The derivation is in most good antenna text books.
\(R_r=\frac{\mu_0c_0}{6\pi}A^2(\frac{2 \pi}{\lambda})^4\\\)The expression depends on an assumption that current around the loop is uniform, so the question is what is the acceptable limit for loop size.
NEC might provide some guidance. A series of NEC-4 models of a octagonal loop of thin lossless wire in free space was constructed with varying perimeter. Perimeter shown is that of a circle of the same area.
Above is a comparison of the two methods of estimation of Rr. To the extent that we trust NEC-4, the graph indicates that error in the simple formula grows quickly for loop perimeter greater than 0.1λ. (The results using NEC-2 are visually identical.)
Many authors set the criteria for a small loop to perimeter<0.3λ, but it is clear that current is not sufficiently uniform for perimeter>0.1λ for estimation of Rr as 31149*(A/λ^2)^2 to 0.1pu error or better.
Small transmitting loop – ground loss relationship to radiation resistance
This article documents a series of NEC-2 models at 7.2MHz of a lossless small transmitting loop near ground for the insight that they might provide about underlying loss mechanisms.
Key model details:
- lossless conductor 25mm diameter;
- octagon of sides 403mm, has same enclosed area as a 1m diameter circle;
- three ground types;
- height varies from 1.5-10m to centre of loop.
Impedance elements discussed in this article are referred to the main loop. Continue reading Small transmitting loop – ground loss relationship to radiation resistance
USBTiny
I bought a USBTiny AVR programmer on eBay for about A$8 posted.
Above, the seller’s pic of the package.
It is almost always the case that the ISP headers on the programmer use the standard pinout published by Atmel, and in that case the supplied ISP cables need to be pinned pin for pin, ie pin 1 to pin 1 etc.
If you look carefully at the pic, the key is towards the top of the pic which means pin 1 on the right hand plug is towards the viewer and pin 1 on the left hand plug is away from the viewer. The cable does not connect pin 1 to pin 1, and as a consequence the package did not work.
There is more than one way to connect these plugs, and above is one way that does connect pin 1 to pin 1, and the cable and USBTiny work. Though the seller has been told of this defect, he continues to sell the item with the pic of the defective cable.
One wonders how many thousands of these things are and will be sold with this defect.
A tale of two USB-RS232 adapters
There are a number of USB-RS232 adapters available, among them Silabs, FTDI, Prolific and WCH.
The Silabs CP series adapters have been reliable but not very widely used.
The Prolific adapters are, well, prolific… but given their major compatibility problems and poisoned drivers, they are not a good choice.
FTDI was a good choice until they distributed through Microsoft Windows Update their device poisoning trick to disable chips they thought counterfeit… though they seemed to have backed away from that action.
The new kid on the block is an adapter by Chinese company WCH, chips that appearing in lots of low cost devices, eg Arduino Nano clones with WCH adapters instead of FTDI selling for around A$3+ on eBay whereas the FTDI equipped Nanos are more like A$12.
This article compares the WCH CH340G and FTDI FT232RL.
Above are two inexpensive adapters for Arduino boards, the upper one is FTDI based at A$8 each (inc post), and the lower one WCH based at 3 for $3.60 (inc post). Continue reading A tale of two USB-RS232 adapters
Cooling an FT2800M
I have described a solution an overheating problem with my IC2200H at Cooling an IC2200H. The Yaesu FT2800M suffers exactly the same problem.
This article describes a thermostatically controlled auxiliary fan to keep the case at a safe temperature.
Above is the test setup: Continue reading Cooling an FT2800M