16

When the tone is present, it is because the antennas are out of phase. One antenna's signal will be leading the other; which one is leading depends on which one is closer to the transmitter (provided that the antennas are less than 1/2 wavelength apart, so that the phase difference will always be less than 180°). When we switch from the lagging signal to ...


12

The best way is to get a high gain antenna, and figure out what direction it's coming from. Do this from 2-3 points. Take a map, and draw lines from each of the point of origins from the direction you heard the signal the strongest. That should give you at least an idea of where the signal is coming from. Once you have a rough idea, the next step is to go ...


7

First, there are better DF antennas now and they take up way less real estate. Some of them are .. the Pusher and "L" and "T" arrays. The electronics for these is more sophisticated than the conventional "Elephant Cage" CDAA but they are faster if the electronics is designed and implemented correctly. The FCC in Laurel Maryland took their CDAA down and ...


6

First of all: why is it surprising that a radio device built in the 1960s has become obsolete? I don't know the specific reasons why this specific type of direction finder has become obsolete, but among these reasons might simply be: cost of renovation > benefit Shift in strategic demand for localization of these boring HF signals instead of a few circular ...


6

Two major reasons HF direction finding arrays like that aren't particularly useful any more (you won't find many fixed HF DF stations at all, even more modern ones): As William said, HF is not used very frequently for military communications these days, it is primarily a backup to satellite systems for long distance communication, and what communications ...


6

It is possible in principle to detect a receiver. Almost all designs of receivers have a local oscillator (LO), which oscillates at the same frequency as the carrier frequency of the signal it is receiving, or at some close offset to it. The signal from the LO can leak back out the antenna. However, in a well-designed receiver this leakage is minimized and ...


5

Yes. Detecting a receiver is VERY VERY VERY hard to do. Since it is only an absorber rather than transmitter of RF energy, it requires a signal strength meter to detect a dip in RF energy. It requires a very directional antenna, and circuitry to detect subtle changes in the signal. This is compounded by the fact that the receiver has a high-gain amplifier ...


5

A few things to start off with: You don't care about efficiency, unless the antenna efficiency is truly abysmal, or your receiver is of very poor quality. Efficiency on the receive side is a measure of how effectively the antenna can couple with the ambient RF field and get that energy to the receiver. Even a receiver of very poor quality will have an ...


4

Essentially this involves using your body as a barrier to fade the signals. Holding the HT close to you, and rotating until you get the weakest signal, then the source of that signal will be on the other side of you. In an answer to a different question, WPrecht - AB3RY quoted the following Handie-Talkie Tricks tip from Joe Moell, KØOV's Homing In website: ...


3

Is it possible to create a circuit to hear (through earphones) or show (with an LED) the direction of a radio source? Yes. There are basically two different types of direction finding techniques: You can simply change the orientation of your antenna and observe whether this makes the received signal weaker or stronger. This has the advantage of working ...


3

If a full-sized VHF antenna is too big, then look at how people do direction finding on HF. A longer wavelengh means bigger antennas, so HF direction finders have been dealing with the "too big" problem for a long time. The canonical HF direction finding antenna is a small loop. This antenna is vertically polarized and gives two nulls when the plane of the ...


3

There are two kinds of "loop antennas". There are resonant loops, which are loops where the length of the loop is long enough to be resonant. These can be considered folded dipoles, which have been folded into a loop. A quite distinct antenna is the small loop. These antennas have a perimeter that is electrically small, meaning less than one-tenth of the ...


3

Here is my dumbed-down experience. If you are looking at T-hunts. I have always made sniffer loops about 1/10th or less then actual wavelength. Many times we would add a trimmer-cap across the antenna feed point but most the time would not. Even before I was a serious ham I did this quite successfully on the CB band for "Skunk Hunts" where we would all ...


3

I would bend the tips back, twisting the free end around the standing end so you make a loop with good electrical contact between them. Measure from the base to the end of the loop for the purposes of calculating the length. The loop is almost entirely cosmetic and won't affect the electrical length of the antenna much. If you were to make the loop bigger, ...


2

Yes they can. You are right that the cheap HTs don't have much of a useful meter (I own a couple). Two easy solutions are 1) body fade and 2) directional antennas. Body Fade Hold your HT close to your chest and turn around slowly, looking for the direction where your body blocks the most signal (the signal null). Now you know that the signal is coming ...


2

You can build a special rig that will give you direction finding capability with a standard radio here: How would a time-difference-of-arrival receiver with two antennas know which side the signal is from? It works by switching between two antennas, located less than a wavelength apart. If the two antennas are exactly the same distance from the ...


2

I think the most important thing to use is a clock. That is, record the times when the interference starts (I know, hard to do at times) and when it ends and even the way it behaves with starts and stops over a period of time. Unless the interference is due to something continuous going on inside the ham's equipment, the interference should not be continuous ...


2

Having worked as an intercept operator at these sites in the 70's I can say that there just isn't anything to intercept on the HF bands anymore.


2

First the answer: When I worked for the forest service I built single-transistor transmitters where one of the leads of the transistor was the antenna. It doesn't get any more simple than that. They used hearing aid batteries. Then we could enclose them in beeswax so we could stuff them down the throats of animals, even snakes. The batteries would last ...


2

I was wondering If I could use an Arduino to find the location of a vehicle using radio. Radio is a pretty big topic, so yes, of course there are ways to use radio technologies to locate a vehicle. There are commercial solutions, but it could also be as simple as leaving a smartphone in the vehicle and using another phone to track it. Whether any of these ...


2

A small loop antenna is bidirectional in the direction of the plane of the antenna and has nulls that are perpendicular to the plane of the antenna. Due to its bidirectional nature, there is ambiguity as to the bearing of transmitted signal when only one receive location is in use. Through the addition of a so called sense antenna, the bidirectional pattern ...


2

Here is where you'll find your answer. http://assets.tequipment.net/assets/1/26/Documents/DF1.pdf Antenna mounting begins on page 17, and on page 19 it shows how the whip antennas are connected to the circuit board. And your answer is Yes, the nut that holds the whip is connected to the circuit board. So the middle of the SMA connector (core, as you ...


2

The demise of the military CDAA is not an issue of capability, accuracy or even economics, but the primary driving factor is the change in mission, targets and technology. HF; whether it's SSB, CW or even digital, is simply not today's prevailing set of tactical or operational frequencies. In addition, satellites and other passive technologies do not ...


2

Wullenwebers have been replaced by the FCC HFDF ("huff-duff") system. Several HFDF installations are located in the USA along both the north and south borders and the east and west coasts, plus Alaska, Hawaii, and other locations such as some US possessions. Most of them are unmanned. Google Maps has a listing of their locations. You can zoom into each ...


1

You have two different use cases. Position reporting and direction finding. Position reporting would be using something like APRS, Automatic packet reporting system. While APRS can transmit different types of data, it is most often used to report positions. A vehicle with a APRS radio will periodically send it position. with a receiver you can get the data. ...


1

Response times are not primarily driven by the antenna characteristics, but the data sampling rate (electro-mechanical, ecectronic, or otherwise), data transmission time (including both receiver's tuning and bearing response) and lastly the ABI calculation algorithms. So, beyond the fixed sampling rate, the biggest limitation is the confidence algorithm in ...


1

I would make something discrete, as sudden changes are easier to detect than large ones. Stick into the middle of the hearing range (Many Hams are older, and tend to lose the extreme hearing range with time). I would choose a random sweep of tones in the 1000-1500 Hz range, changing the tone 2-5 times per second (Random time intervals might also work). This ...


1

If it is from the ham, I would expect the following characteristics: It would be intermittent, only happening for a few seconds to a minute at a time. Hams generally communicate in a conversation with modest length monologues, so the interference will probably come and go a bit like that. Also, it'll probably be only a few hours per day - even if he's ...


1

If a simple magnetic loop antenna is what you want, you should have a look at http://www.m0ukd.com/Magnetic_Loop/ The loop he constructed is about 10cm in diameter (which is approx. 4 inches) which is not that much to carry around. For 70cm you might want to go for a small Yagi design since it provides you with some additional gain. For a 4-Element yagi ...


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