A library of “standard” component values is included to make more realistic component selections. It allows an SWR circle to be shown around a designated load and rapidly view Smith Chart or VSWR plots w/power line. It’s free, and he has several video tutorials that help gain acquainted with the many embedded features. The new graphical tools remove much of the math making life much easier.Īnother Smith Chart tool mentioned last night is SimSmith which is available at: There is always a large focus on antennas and the topic of making good or acceptable SWR choices is almost always an issue.
Formulas en qucs software#
Jeff, WA1HCO Antennas Elmer HF Homebrew Software Tech Night Post navigation This shows that it can work with data from an antenna model or analyzer and can optimize matching networks to create a broadband antenna. Put in one less stage of L-C and the ripple across the passband goes up a bit. But, the 160 network doesn’t really need 7 components. Building that network to handle Tx power will require vacuum variable capacitors in parallel with high quality stable fixed value capacitors. The 160-meter network has some extreme values and it is probably very touchy to get right. I have not built any of these networks to see how they work in practice. This network uses capacitors and inductors because coax stubs would be very long on 160 meters.
It achieves about 1.7:1 across the whole band. The blue curve shows the result of an optimization run that selected the values for a 7 component matching network. The red curve in the plot below shows a top loaded 160 meter vertical. The loading makes the match very narrow-band. 160-meter antennas are often implemented as shortened loaded verticals. The line lengths predicted by the model are… Line 1 and 3 are configured as open stubs. The actual matching network consists of Line 1, 2, 3, 4. The model of the antenna is stored as a file in the X1 file component. This network is designed with coaxial stubs. I drew a general filter network and let QUCS tune the component values. QUCS achieved this by varying the components of a filter network. QUCS has designed a broadband matching network that can achieve less than 1.5:1 SWR over the whole band. Here is the result from running the optimizer on the data for my mistuned 40M dipole. In the terms that QUCS understands, “minimize the maximum SWR over the frequency range 7.00 to 7.35 MHz. For the case of a broadband antenna, “The worst case SWR anywhere in the ham band shall be as low as possible”.
The optimizer setup needs a definition of “optimal”. It has the ability to try hundreds of circuit values and home in on an optimal design. Or the data can come from a measurement made by a good antenna analyzer. The antenna data can come from either an antenna modeling program such as 4NEC2 or EZNEC. The QUCS RF circuit simulation program has the ability to model SWR, bandwidth, matching networks based on data about antenna performance. In fact, the extra tuned circuits generally act to make the antenna have even less bandwidth.
Formulas en qucs manual#
Modern radios have built in automatically adaptive matching networks make the radios work over a wider bandwidth, but networks are lossy and reduce transmitted power.Ī manual antenna tuner has a lot lower loss than the built in tuner, but it requires manual adjustment. It’s a good match at 7.000 MHz and degrades to about 2:1 at 7.100 MHz.
Here’s a plot of the SWR for my 40 Meter Dipole. The 75/80 meter band has a wide bandwidth in term of percentage. Shortened or loaded antennas have a narrow range of match frequencies. Some bands and antennas are more challenging to match than others. The antenna has the best match at one frequency and the match gets worse as the operating frequency changes. Transmitters want to see a matched antenna with an impedance of 50 ohms.
This will be a described in more detail at the September Tech Night.Īntennas have an impedance (or match) that varies with frequency. This article discusses some work on designing a matching network to make antennas match well (low VSWR) across the entire ham band.
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