Sunday, 19 July 2020

Fieldstrength meter

I replaced an insensitive VU meter by a 100 uA meter on my fieldstrength meter:



This meter uses a quadrupler circuit to increase sensitivity:



The Ge-diodes (OA85) make the meter useable even above 500 MHz.

Friday, 17 July 2020

nanoVNA

I just couldn't resist.

Ordered a nanoVNA that arrived yesterday.

I was able to do my first antenna analysis after looking at some youtube movies.



Here you can see a homebrewed 2 m antenna under test. A nice dip exactly on 144 MHz in the attenuation trace. The Smith chart shows almost a 50 ohms impedance (the green triangle near the centre).

It is an impressive toy for a few bucks (aliexpress, amazon). It enables you to analyse antennas, filters etc. from 50 kHz - 900 MHz !



Wednesday, 15 July 2020

No decrease in global CO2 concentration during the early COVID-19 era

At Mauna Loa, Hawaii, since 1960, the CO2 concentration is measured. 

Around 1960 the CO2 concentration was about 315 ppm (parts per million). In 2020 the concentration has increased to a level of about 415 ppm. Generally, it is believed that this CO2 increase is caused by anthropogenic emissions ('human caused' emissions) and is the main reason for global warming.








Fig 1 CO2 concentration at Mauna Loa, 1960-2020

Note: the 'sawtooth' pattern you see is caused by seasonal influences (the presence and absence of the green parts of trees/vegetation).

Since the start of the COVID-19 pandemic, the CO2 emissions from the burning of fossil fuels have dropped dramatically. It is estimated that the global CO2 emissions dropped with an average of 17% starting April 2020. Peaks of around 26% have also been noticed.
However, in the most recent graphs we do not see a decline in CO2 concentrations at all:




Fig. 2 Last 2 years

CO2 is a so called well mixed gas that spreads within a few weeks in the atmosphere. But even after a couple of months after the start of the corona wave, we do not see major changes in the Mauna Loa CO2 concentration trend.

Other global CO2 monitoring laboratories show the same behaviour as the Mauna Loa laboratory with respect to CO2 concentration.

One can consult the Mauna Loa data here:

https://www.esrl.noaa.gov/gmd/ccgg/trends/graph.html

This might be a good time to adjust the CO2-prediction models based upon the data gathered in the early corona period. The contribution of anthropogenic CO2 emissions to natural CO2 emissions might be far less then we thought. Administrations should be more reluctant with spending trillions on projects that might reduce CO2 emissions.
The most common greenhouse gas is water (water vapor/clouds). The effect of water as a greenhouse gas might be underestimated; Although the GWP ('global warming potential') of CO2 is much higher than that of H2O, the presence in the earth's atmosphere of CO2 (0.038%) is so much smaller than that of H2O (0.5%..7%) .

Saturday, 11 July 2020

VHF/UHF logper antenna

This week I finished a dualband logper antenna.

It is a design according to Gunter, DL9HCG.
Construction details can be downloaded here: https://dl9hcg.a36.de/

Logper antennas are also called LPDAs (Log Periodic Dipole Antenna).

The advantage of a logper (logaritmic periodic) antenna is its  large bandwidth combined with relative small dimensions.

I selected a 7-elements logper with following dimensions:




One starts with the construction of a dual boom

7 element logper



Measured SWRs:

430 MHz  1 : 1.4
145 MHz  1 : 1.6

First QSOs with the repeater in Goes 145.775 MHz and 438.400 MHz  PI1ZLD are promising.
http://www.pi3goe.nl


Logper pointing in the direction of the Zierikzee repeater