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There has been a lot of discussion lately, much of it just plain incorrect, about the relationship between resonance and antenna efficiency. Many incorrectly claim that resonance has nothing to do with antenna efficiency at all, similarly others incorrectly claim that resonance is a direct indication of efficiency. Neither of these statements is true. The reality is that resonance does have a significant impact on how efficient your antenna is, but the relationship is highly non-linear and depends on many characteristics.

Below I have attached a chart hat plots out the total radiation resistance (R_r) vs the measured input resistance (R_in) of a dipole. Efficiency is just R_r/R_in. In other words an efficient antenna will have 100% of its resistance as radiation resistance, and R_in is **always** larger than R_r (since it is essentially ohmic resistance plus radiation resistance). When these two numbers differ significantly an antenna is inefficient. The source for the chart below is here and it gives much of the math if you want a deeper dive:

https://nptel.ac.in/content/storage2/courses/108101092/Week-2-Dipole%20Antenna.pdf

What is important to note here is that at anti-resonance we see a **huge** R_in value and a small R_r value, this means an anti-resonant antenna will have very high losses. Keep in mind the graph is very hard to read for the values <0.5 in length because the resolution isnt high. But there is significant divergence there as well. Notice at ~5/8ths wavelength antenna would exhibit very significant internal ohmic losses due to heat.

#hamradio #rf #radio #ee #electronics #electricalrngineering @Electronics


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#HamRadio #AmateurRadio


Hacked together an ultraportable HF antenna system to work well between 3.5Mhz - 200 MHz (80 meters - 2m) frequencies. Basically took a coil loaded GRA-1899T antenna with telescoping antenna, added some off-the shelf BNC adapters and did some minor hacking. To make it work I had to remove the center connector from two of the BNC adapter s(marked with an X in the diagram). Then added a short-circuit BNC connector, which connects the otherwise floating center connector from the bottom half to ground/shield enabling the counterpoise. Added two additional telescoping elements for the counterpoise and we have a complete system.

The thing I like about the approach is the modularity. For example I can remove or add normal t-connectors to change the number of counterpoises used. The setup pictured uses 2 counterpoises but it would be trivial to setup 1 to 4.

Also the short circuit connector (pictures here as the black and teal connector with the short circuit in it) can allow me to do multiple things if i want to get more complicated. For example if I want to remove the short circuit I can replace it with coils or capacitors for additional tuning. I can also leave it as is but connect an earth ground to it to improve the effectiveness of the counterpoise.

A final note, the loading coil attached to the radiating part of the antenna has a jumper with 6 different positions. This lets you manually adjust the size of the loading coil for different frequencies. Fine tuning is accomplished by changing the length of the antenna itself.

#Science #electronics #RF #radio #Amateur AmateurRadio #HAM #HAMRadio ## @Science





Some pictures of my APRS station brought back to life. Currently being heard in Ireland, Canada, Germany, and Washington state (I'm on the opposite coast).

#ham #hamradio #radio #RF #EE #Electronics #AmateurRadio @Science



Sweet, just brought back up my APRS radio station transmitting on both VHF and HF frequencies. Looks like it is working great I am being heard in both Ireland and Canada on the HF side!

Can't wait to get back to coding PEAK (the APRS software I run that runs a next gen version of APRS I am developing).

https://aprs.fi/info/WI2ARD

@Science #ham #hamradio #radio #RF #EE #Electronics #AmateurRadio

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