Feasibility study – loop in ground for rx only on low HF – signal / noise degradation (SND) gave the following graph.
This article explains a little of the detail behind the graph. Continue reading Loop in ground (LiG) – #7 signal / noise degradation (SND) – more detail
Feasibility study – loop in ground for rx only on low HF laid out an initial design concept. This article sets out expected signal / noise degradation in a typical installation.
Let’s take ambient noise as Rural precinct in ITU-P.372-14.
An NEC-5.0 model of the 3m a side LiG gives average gain -37.18dBi. An allowance of 2.7dB of feed loss covers actual feed line loss and mismatch loss. Continue reading Loop in ground (LiG) – #6 signal to noise degradation (SND)
The nature of radio signals received off-air is that they are accompanied by undesired noise.
A key measure of the ability to decode a radio signal is its Signal to Noise ratio (S/N) at the demodulator (or referred to some common point).
We can speak of, think of, an external S/N figure as \(S/N_{ext}=10 log\frac{S_{ext}}{N_{ext}}\) in dB.
Receiver systems are not perfect, and one of the imperfections is that they contribute undesired noise. Continue reading Signal to noise degradation (SND) concept
A recent online discussion tried to advise on the need of a common mode choke on a UHF Yagi.
Above is the subject M2 440-6SS, 420-450 MHz Yagi deployed in vertical polarisation (using the other pair of holes for the U bolt). Continue reading Gamma matches get blamed for a lot of stuff
On testing two wire line loss with an analyser / VNA – part 3 showed how to estimate two wire line characteristics from dimensions and an estimate of velocity factor. This article does the same for a coax example
To take an example, let’s use one posted online recently:
Stranded Tinned copper center conductor, 0.037″ od Solid, white dielectric (not foamed), 0.113″ od Od of jacket, 0.196″
The dimensions we are interested in are OD of dielectric, 2.97mm (0.113″) and OD of the inner conductor, 0.989mm (0.037″). A solid white dielectric (as opposed to translucent) is likely to be PTFE which has a velocity factor around 0.7 (in most PTFE cables) and we will assume a loss tangent of 1e-4 (typical of non-polar polymers). Continue reading Estimating characteristics of a sample of coax from dimensions and properties
This article series shows how to measure matched line loss (MLL) of a section of two wire line using an analyser or VNA. The examples use the nanoVNA, a low end inexpensive VNA, but the technique is equally applicable to a good vector based antenna analyser of sufficient accuracy (and that can save s1p files).
On testing two wire line loss with an analyser / VNA – part 1
This article series shows a method for estimating matched line loss (MLL) of a section of two wire line based on physical measurements (Duffy 2011).
Above is a short piece of the line to be estimated. It is nominal 300Ω windowed TV ribbon. It has copper conductors, 7/0.25, spaced 7.5mm. The dielectric is assumed to be polyethylene… but later measurements suggest is has slightly higher loss than polyethylene. The test section length is 4.07m. Continue reading On testing two wire line loss with an analyser / VNA – part 3
This article series shows how to measure matched line loss (MLL) of a section of two wire line using an analyser or VNA. The examples use the nanoVNA, a low end inexpensive VNA, but the technique is equally applicable to a good vector based antenna analyser of sufficient accuracy (and that can save s1p files).
On testing two wire line loss with an analyser / VNA – part 1
Above is a short piece of the line to be measured. It is nominal 300Ω windowed TV ribbon. It has copper conductors, 7/0.25, spaced 7.5mm. The dielectric is assumed to be polyethylene… but later measurements suggest is has slightly higher loss than polyethylene. The test section length is 4.07m. Continue reading On testing two wire line loss with an analyser / VNA – part 2
This article series shows how to measure matched line loss (MLL) of a section of two wire line using an analyser or VNA. The examples use the nanoVNA, a low end inexpensive VNA, but the technique is equally applicable to a good vector based antenna analyser of sufficient accuracy.
Above is a short piece of the line to be measured. It is nominal 300Ω windowed TV ribbon. It has copper conductors, 7/0.25, spaced 7.5mm, though as can be seen the spacing is not perfectly uniform. The dielectric is assumed to be polyethylene… but later measurements suggest is has slightly higher loss than polyethylene. The test section length is 4.07m. Continue reading On testing two wire line loss with an analyser / VNA – part 1
I have a Toro ride-on mower which ran out of fuel when it was just a couple of years old, perhaps 50 hours on it. Okay, so that is going to happen with failure to check fuel level before starting… but the problem was that when the tank was filled, it would not start, the petrol pump would not self prime even though the suction head was very small with a full fuel tank.
Mindful that long cranking is very hard on batteries, I used the starter sparingly in short bursts with cooling off time. Nevertheless, the battery went open circuit.
So I replaced the battery and primed the pump by hand… and all has gone well for some years… until last week, I ran it out of fuel, duh!
Same problem, when the tank was filled, the pump would not self prime.
The machine has a problem that needs to be fixed.
The inline filter was checked, and fuel flowed though it quite well by gravity. This time, I primed it by hand early in the process and got on with mowing. This was probably not a vapor lock problem, everything was quite cool by the time I fueled the machine. Continue reading The mower appears affected by Ethanol
I have a chipper / shredder that has a Briggs and Stratton 6.5hp (~5kW) Intek I/C 206cc engine on it.
On a recent routing maintenance inspection, I dropped the carburettor bowl to look for signs of Ethanol damage (mainly corrosion). During that inspection I noted that the bowl gasket was hardened even though the engine is only 13 years old, and that a stain on the mulcher body hinted a fuel leak even though the bowl exterior seemed dry on test..
The machine is usually stored with the petrol cock off, so the opportunity for a needle / seat leak would be during a day’s yard work where the petrol cock is on for hours but the machine is run for a lesser time.
A pressure test might provide a firm diagnosis.
A piece of silicone tube was connected to the carburettor in place of the normal fuel hose, a little petrol added to the hose with a pipette, and then a sphygmamometer used to pressurise the hose.
Above, the test in progress. The fuel level in the hose can be seen about 30mm from the end. The pressure is leaking down quite slowly, the leak is not fast enough to upset engine operation (by flooding or even an over rich mixture) but it might well result in dilution of the crankcase oil when the engine is left standing. It needs repair. Continue reading The mulcher appears affected by Ethanol