This posts shows a measurement of ambient noise and comparison with the data given at Expected ambient noise and its more detailed references.
The test scenario is my 40m station, a G5RV inverted V dipole with tuned feeders, a balun and ATR-30 ATU. Antenna system losses are less than 1dB.
The chart above gives a range for expected ambient noise at 40m.
Above is a screen shot from a spectrum analyser measuring power in 1kHz bandwidth from 7.0 to 7.1MHz. The band is mostly unoccupied, and the mean noise power is about -99dBm, it would be 3dB higher in 2KHz bandwidth (ie -96dBm). Continue reading Expected ambient noise – in practice
One of the casualties of the cessation of VK1OD.net was an article on expected ambient noise.
The original work was based on ITU-R P.372-8 which has been updated to -10 and now -12, but the updates do not alter the basis for the original article.
Since the work was a reference cited on my FSM pages, it has been updated and copied to Expected ambient noise level. The graphics and tables in the article and the PDF file all refer to ITU-R P.372-8 but remain correct wrt ITU-R P.372-12 (2015).
This article documents an implementation of PAROT (Power Amplifier Run On Timer) using Transformerless power supply for PAROT.
This PAROT uses a 10A SSR for 230V mains switching and does not include PTT switching, but space exists for a FOD852 opto coupler for PTT switching.
The immediate application is to control my main station power supply so that if it has been in use, is hot and fans are running, the PAROT provides in this instance a 5min cool down before powering down.
Above is the electronics built on a small piece of Veroboard.
Above is the copper side of the Veroboard. The layout is designed to accomodate another implementation using a small Triac to switch a 230V AC relay. The board has been given a heavy coat of acrylic PCB lacquer to improve voltage withstand.
The PAROT is assembled inside a small die cast aluminium box with stick-on rubber feet.
Above is a view of the interior of the box. A 430V MOV is connected across the SSR output terminals, it is not clear whether the device has internal protection (Chinese product, very brief data). The LED / momentary switch on the right is the only control and indicator for PAROT operation. Note that because of the transformerless power supply, everything inside the box is potentially at mains voltage… a fact that must be kept in mind when working on it. An isolation transformer is a worthwhile tool for working on these type of things. Continue reading PAROT with transformerless power supply and 10A SSR
(Dunlavy 1967) sets out his description of a wide range tunable transmitting loop antenna and makes a broad efficiency claim of better than 30% (-5.3dB) for his system.
Minimum efficiencies of 30 percent are attainable with practical designs having a diameter of only 5 feet for 3-15 Megahertz coverage.
In a context where extravagant claims are often made for such antennas, his claims warrant review.
Dunlavey gives an example embodiment in approximate terms.
Practical loop designs for use in the range of 2-30 megahertz will utilize copper or aluminum tubular conductors having a diameter of 3 inches to 5 inches. A typical design for 3 to 15 Megahertz operation would be constructed as shown in FIG. 2 with a primary loop 4 having a diameter of about 5 feet and tuned by a high voltage vacuum capacitor 5 having a capacitance range of approximately 25 to l,000 picofarads. The tuned primary loop should be made of aluminum or
copper tubing having a diameter of approximately 4 inches-5 inches. The diameter of the feed loop, which is designated by the reference number 6, for 50 ohms impedance should be approximately l0 inches.
Lets take a perimeter of 4.8m (dia=5′) and copper conductor diameter of 100mm (4″) as the dimensions for further exploration.
Above, Dunlavy’s Figure 5 gives gain relative to a monopole above perfectly conducting ground. Continue reading Review of Dunlavy’s STL patent gain claims
I use a number of implementations of the DS1307 or DS3231 Real Time Clock chip, preferably the latter these days as they are considerably more accurate and compatible with DS1307 code.
In some applications, it is necessary or sometimes just better to preset the clock before connecting it into the application, and the need arises to set the clock ‘stand alone’. The method I have used for this has been clumsy and not as accurate as one might want for the DS3231, so this article describes a new solution.
The solution uses an Arduino as the engine if you like. Above is an Arduino Pro, but a range of similar Arduinos would be equally suitable. ALso pictured are three RTCs, one connected to pins A2, A3, A4 and A5 providing GND, VCC, SDA and CLK respectively. Continue reading Arduino app to set DS1307 Real Time Clocks.
Designs appearing in the ham literature and online articles tend to espouse relatively large diameter conductors, conductors that can be challenging to wind onto the toroidal cores often used.
This article analyses the copper losses in a practical Guanella 1:1 balun where a fabricated twisted pair line is used.
Total losses comprise core losses and transmission line losses. Continue reading On copper loss in transmitting baluns
This article documents initial tests on a MultiStar 5200mAh 3S Lipo.
Two of these were purchased for about A$24 ea + delivery from the HK Australian warehouse.
On delivery, the batteries were served a balance charge to full capacity.
Above, one of the batteries with the usual mods to suit my quadcopters. A heavy heatshrink encapsulation to reduce the risk of battery damage from crashes and flying propeller bits, rocks etc. A little velcro path to help stabilise the battery on the quad, a ‘gripper’ for the balance plug, balance plug secured to keep it out of the props, and a charge indicator for convenience.
Continue reading MultiStar 5200mAh 3S Lipo – initial tests
Finding resistance and reactance with some low end analysers #2
Exploiting your antenna analyser #8 was about finding resistance and reactance with some low end analysers that don’t directly display those values of interest. The article showed how to calculate the values starting with |Z| from the analyser and included links to a calculator to perform the calcs.
This article describes an extension to that calculator Find |Z|,R,|X| from VSWR,|Z|,R,Ro to use R, VSWR, and Ro as the starting point. Note that the sign of X and the sign of the phase of Z cannot be determined from this starting point, there just isn’t enough information.
You will probably not find the equation for |X|(R,VSWR,Ro) in text books or handbooks, and the derivation is not shown here but if there is interest, I may publish a separate paper.
Lets say you knew VSWR=2, R=75Ω, Ro=50Ω, what is |X|?
Above, entering the values in the calculator we find that |X|=35.4Ω. Continue reading Exploiting your antenna analyser #20
A correspondent having read Analysis of a certain dipole animation questioned the validity of the lossy transmission line model of the dipole, citing the case of an OCF half wave which has an approximately resistive feed point.
Since the OCF lacks the symmetry exploited in earlier study, we must consider each half of the OCF dipole and combine them. To assist, I have produced a similar plot of the transmission line but note the changed X axis.
The scenario is again a 2mm diameter copper wire, 3m above ground at 1MHz.
Zo can be approximated as 138*log(2h/r)=138*log(2×3/0.001)=521Ω.
Above is a plot of calculated V and I at displacements from the open end, and calculated phase of V/I. Continue reading Analysis of a certain dipole animation – OCF implications
Critically review your measurements
A recent post on an online forum provides a relevant example to discussion of this subject.
I have personally seen ratios similar to 3:1 or higher at the feed point become 1:1 at the rig over 100 or so feet of coax cable.
First point is that in good transmission line, it takes an infinite length to deliver the observations made above. Less might deliver almost VSWR=1 at the input end of the line.
Let us consider a practical scenario, 100′ of RG58A/U with a load of 150+j0Ω at 14MHz, the load end VSWR(50) is 3, the input impedance is 32.50-j22.86Ω and input VSWR(50) is 2.01. In this scenario, the line loss is 2.5dB which might be unacceptable for some applications. Continue reading Exploiting your antenna analyser #19