It sometimes seems as though antennas and RF design are portrayed as something of a Black Art, the exclusive preserve of an initiated group of RF mystics and beyond the reach of mere mortals. In fact though they have their difficult moments it’s possible to gain an understanding of the topic, and making that start is the subject of a video from [Andreas Spiess]. Entitled “How To Build A Good Antenna”, it uses the design and set-up of a simple quarter-wave groundplane antenna as a handle to introduce the viewer to the key topics.
What makes this video a good one is its focus on the practical rather than the theoretical. We get advice on connectors and antenna materials, and we’re introduced to the maths through online calculators rather than extensive formulae. Of course the full calculations are there to be learned by those with an interest, but for many constructors they can be somewhat daunting. We’re shown a NanoVNA as a useful tool in the antenna builder’s arsenal, one which gives a revolutionary window on performance compared to the trial-and-error of previous times. Even the ground plane gets the treatment, with its effect on impedance and gain explored and the emergence of its angle as a crucial factor in performance. We think this approach does an effective job of breaking the mystique surrounding antennas, and we hope it will encourage viewers to experiment further.
If your appetite has been whetted, how about taking a look at a Nano VNA in action?
13 thoughts on “What Makes A Good Antenna?”
There are some additional things to consider for antennas, in addition to the RF stuff:
– make it mechanically stable enough (mentioned briefly). For example, if it will be mounted outside, it has to hold up in strong winds. And not become a hazard for other people.
– If it will be used inside, dont create an “eye-poker”
– If it will be used outside, consider corrosion. Select metals that can exist together without one of them dissolving.
– If it will be used outside, consider lightning.
– Most asymmetrical antennas, like the ground plane, benefit from a good earth connection. The lower the frequency, the more important.
– Every antenna has regions where the “RF-current” dominates the “RF-voltage”. Make sure you have very low Ohms resistance where the RF-current is.
Many things missing here. You pick an antenna that suits the application. Bandwidth, pattern, location, size, cost, environmental, etc. Most antennas presented here are narrow band, vertical polarization. If you don’t care that 90% of your power heads skyward, OK. Cable matters. Cheap RG178 can have over 1dB per foot attenuation. SMA connectors have a limited number of mating cycles and should be torqued to a specific value with a torque wrench. N connectors are waterproof. UHF are not. There are thousands of designs because there are many different use cases. What might be good for one application is useless for another. It isn’t magic but you really need to understand your constraints and tradeoffs. Then you pick from the dozen or hundred variations best suited to your needs.
if you leaving your antenna outside on the roof consider storm and lightnings!
It’s Andreas Spiess not Speiss ;-)
Does it beat a rusty nail?
Brilliant video, It demystified the antenna stuff for me. I have always wondered how antennas works (via black magic?), and this video helped me a bit out of the dark, I am looking forward to a sequel from Andreas.
@Jenny: Noticed a small typo: his name is Spiess*, not Speiss.
Coat-hangers … coat-hangers make good antennas… I’m only half joking… things I’ve “thrown together” more or less wavelengthy out of coat-hanger wire seem to have a habit of working better than carefully measured and constructed ones out of 12g copper. I’m not transmitting off any of them though, nor am I expecting the elements to survive the elements.
Then there’s abominations like the “bat wing” which was an “oh crap I need to test this TV card” (and my decent antennas don’t reach here, and I don’t want to disturb) so marked a soda can, to give me the longest pair of equilateral triangles, chopped them out, screwed them to a block of wood with the coax, and yay, reception. (Sanded around screw/cable area to get bare metal for connection) … it seems to do as good as 6dB on UHF-lo, not sure on VHF-hi, there’s 3 strong ones I’m almost on top of, so those come in easy. Anyway, it gave me enough channels to check things out, play with recording. It was encouraging enough that I might make a 4 bay bowtie like that when I get the itch. Kinda floppy though, attic only.
When I was young, my parents have a techincan installed a high gain fishbone TV antenna. The reception was lousy. As time goes on more and more of the segments falls off (during huge storms etc), it got better and better. I think we had it down to the loop at some point.
As my own experience, I got better receptrion off a hacked together TV – RF board from broken TV found on curbside with my Amiga monitor and a coat-hanger vs my housemate’s TV. These days I am using a foam board + tin foil antenna to receive OAT digital TV. It has similar performance as my $5 planar TV antenna I got off as a special.
I’ve made many coat hanger ants with only a moment to briefly guestimate wavelength. Many times I’ve been surprised to find them still in use years later, with users saying they didn’t know where it came from but it was the only ant that worked lol.
Later in life I discovered steel fixers tie wire. Double it over and twist into a braid. I like to keep a 1″ loop at end. 1xFits perfectly into the hole left behind when a telescopic ant gets snapped off.
Can get signal nearly twice as far out as original telescopic.
ARRL books are inexpensive and a great place to start for both practical and theoretical knowledge.
What I liked about this was the introductory info on using the Smith chart from a VNA to drill in to what makes an antenna perform well.
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