16
votes
Accepted
Can I build a radio telescope out of a parabolic TV satellite dish?
The primary factor to consider is the directivity of the parabolic antenna. It is given as:
$$d=\frac{(\pi D)^2}{\lambda^2} \tag 1$$
where D is the diameter of the dish and $\lambda$ is the ...
- 18.1k
13
votes
Can you use a satellite dish for a ham radio antenna?
You can use a satellite TV dish antenna for amateur radio use but how you use it depends on what frequency you want to operate on.
The satellite dish antenna is two basic parts, the parabolic ...
- 332
12
votes
Accepted
Does a receiving antenna need radials?
Most antennas are reciprocal — they have the same properties when receiving as when transmitting. This means that in many ways, a good antenna design makes both a good receiving antenna and a good ...
- 22.7k
11
votes
Accepted
Is an antenna analyzer necessary for building antennas?
I've not personally built antennas from scratch, but I appreciate my antenna analyzer just for being a good instrument — making the invisible aspects of my antenna system visible.
Compared to using ...
- 22.7k
10
votes
Accepted
Dipole Antenna Current Distribution at any Time Instant
You have aptly discovered why a balun is necessary when feeding a dipole with coax. You are right to think the book is wrong, because it is. With a coax feed and no balun, the current distributions on ...
- 49.8k
10
votes
antenna in the rain
The antenna itself won't be significantly affected by the water.
However, waterproofing the coax connection is essential. If this is not done, water will creep inside the coax by capillary action and ...
- 49.8k
10
votes
How do VHF antennas compensate for change in frequency in Frequency Modulation?
All modulated signals, not just FM, have a bandwidth. The antenna has a bandwidth, which must be wider than the modulation of the signal you are using.
Note that receive bandwidth and transmit ...
- 4,188
9
votes
Accepted
How to combine two 50 Ω antennas such that they appear as one 50 Ω load?
The canonical solution to this problem is a Wilkinson power divider. There are of course other power dividers, but the Wilkinson is easy to fabricate, provides good isolation between the output ports, ...
- 49.8k
9
votes
What ways are there to extend an antenna?
You have an SMA connector – use that! You can buy ready-made coax cables with SMA connectors on both ends.
As mentioned, what you want is a coax cable. The electromagnetic wave travels within the ...
- 13.3k
9
votes
Accepted
Why are there differences in antennas that depend on electrical component and magnetic component of a radio wave?
In free space, the electric and magnetic fields are always in a fixed ratio, a physical constant called the impedance of free space, about 377 volts per ampere. The two are always in phase (and thus ...
- 49.8k
8
votes
How to determine if my antenna is an effective radiator?
If you have a field strength meter, then you can use that. You can also use a 2nd radio, on a 2nd antenna.
But, consider reciprocity: anything you to do increase your transmit gain also increases ...
- 49.8k
8
votes
Accepted
What is the velocity factor of a wire?
A coaxial cable is a transmission line by itself, and therefore the velocity factor is known. It depends on the dielectric properties, geometry, and conductivity.
A single wire is not a transmission ...
- 1,099
8
votes
Accepted
Tuning/trimming a ground plane antenna
My trick is instead of cutting, rather extend the whip first, and see if the SWR gets better or worse. Extend it 1/2" with a bit of wire wrapped around it and sticking out. If the SWR gets better, ...
- 7,827
8
votes
Wider wire = picks up more energy, yah?
In short, no.
In long, it's really complicated. The wider your wire, the wider the bandwidth, due to the increase in available paths. Wide multi-strand wire does better against skin effect (more ...
- 81
8
votes
Aluminum vs copper antenna element lengths
Besides mechanical differences, the primary difference between aluminum and copper in antenna construction is RF resistance. Copper will have slightly less RF resistance for the same surface area. ...
- 18.1k
8
votes
Will stainless steel bolts work with my copper antenna?
Stainless steel fasteners, lead and tin are compatible with copper. Lead tin solder, however, has poor mechanical strength as you have apparently discovered. Solder can be used to improve conductivity ...
- 18.1k
8
votes
Wire antenna slightly too long
You should not make any coil in the middle of the antenna as that will greatly change its RF characteristics. Instead, bundle up the wire at the ends in some fashion:
One practical solution is to ...
- 22.7k
8
votes
RigExpert AA-35 - Interpreting The Information
First, a general statement: the antenna analyzer has one set parameter, the frequency, and one measured parameter, the impedance (which is a complex number and therefore requires two real numbers to ...
- 22.7k
8
votes
Antenna Basics - Open/Short Circuit & Half-Duplex/Full-Duplex
My Understanding 1 - Antenna is just a piece of a metal conductor. "Antenna is an OPEN CIRCUIT, and not a SHORT CIRCUIT". Is my understanding correct that the Antenna is an open circuit and not a ...
- 22.7k
8
votes
Accepted
What's the proper way to mount antenna mast to the side of a house?
I know that the gap between the wall and the antenna mast that would be created using the wall mounts you mention is not for lightning damage prevention purposes. If a bolt of lightning can travel ...
- 8,922
7
votes
Accepted
What is the attraction of vertical antennas for HF?
Cribbing a few quotes from answers to related questions, here's a start.
From https://ham.stackexchange.com/a/195/1362:
The primary advantages of vertical antennas are that they are ...
- 5,975
7
votes
Do PCB antennas suit for NOAA and ADS-B?
PCB is an appropriate and useful way of making antennas for higher frequencies, say from 900 MHz and up.
My company made thousands of GSM antennas for window mounting (in the days of car-installed ...
- 7,827
7
votes
Accepted
RF Antenna - V pole - Should one leg go to ground and the other to signal?
One leg of the antenna goes to the center conductor and the other leg of the antenna goes to the braided shield of the coaxial cable. The terminal block is just a way to make the connections, and it ...
- 22.7k
7
votes
Accepted
3 Band (80-40-20 Meter) Fan Dipole Tuning Question
Before getting to the questions you asked, an observation: the design doesn't appear to include a balun. Adding one is probably a good idea.
Is there a way to flatten the SWR in this range [80m] or ...
- 49.8k
7
votes
How do VHF antennas compensate for change in frequency in Frequency Modulation?
Or does this antenna have a frequency tolerance?
This is closest, but the antenna, itself, does not actually have a “frequency tolerance” (more usually called a bandwidth). Rather, the antenna's ...
- 22.7k
6
votes
Accepted
Weather-proofing antenna connections
What I have done once for a dipole was use a SO-239 panel receptacle with a solder cup to make my own "coax to two wire" adapter. For example, I used something like this part from Mouser. That way, I ...
- 1,871
6
votes
How to detect common-mode currents or “RF in the shack”?
Another way to detect current on the outside of coax is to run your hand up and down the coax wile an analyzer is connected , if you see a fluctuation on the meter then current is following on the ...
6
votes
Steel Directors with Copper DE
It's probably OK to use a different metal for the directors than the driven element, as long as you don't have dissimilar metals touching that would create a galvanic corrosion problem. But steel is ...
- 8,922
6
votes
Accepted
Hentenna beam...is it possible?
Let me combine the following statements of your question
I want to explore (the strange new world of creating a beam antenna)
to boldly go where no man has gone before
Would the perpendicular rods ...
- 2,077
6
votes
Accepted
Effect of paint / uv coating on velocity factor of PVC
No.
Even if the electromagnetic material properties of the paint were drastically different than that of air, the few microns of coating won't be even measurable. (Unless that coating really is ...
- 13.3k
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