Fox hunt loop. Null and peak?

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Jhernan488

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Hello,

I bought the fox hunt loop from arrow antenna. I'm confused on how to use this for finding the transmitter as I am new to fox hunts.

What is the null, how is it used to find the transmitter? What does it do? Will it be a loud/quiet signal?

What is the peak, how is it used to find the transmitter? What does it do? Will it be a loud/quiet signal?

I do have an attenuator, too. Works with 4mhz steps.
 

vagrant

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Null = Weak or no signal
Peak = Strong or loudest signal

Think of the loop as a rolling wheel, taking/aiming you in the direction you want to go. The thing is, with a loop like that, when you hear/see the peak signal you need to know which direction. That can be done with a technique called body fade. Hold the loop in front of your body and slowly turn your body 360 degrees. Somewhere during that turn the signal will get stronger and weaker. If you need to, spin again and again. Once you find the stronger signal direction, move in that direction. How far is an unknown. That is the art of direction finding.

At some point when the signal is strong, no matter which way you turn, that is when you start using the step attenuator. Then start the process over again.

If a local club is putting on the hunt, ask ahead if you can ride along with someone. If it is on foot, see if someone will let you pair up so that you can watch and learn.

I figure there are web pages providing plenty of information, as well as video tutorials. No need for me to write out what others have already done. Still, you may have questions after reading or watching videos. Come back and ask, happy to help.
 

K4EET

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Generally, speaking, on most DF antennas, the nulls of the radiation pattern are sharper than the peaks. What that allows one to do is to get a better reading on the direction of the Fox. That being said, like vagrant said above, see if you can ride along with somebody on your initial Fox hunts. You can watch them use their equipment and they can watch you use your equipment. That will get you off to a good start in DFing. It is a lot of fun!
 

dlwtrunked

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Hello,

I bought the fox hunt loop from arrow antenna. I'm confused on how to use this for finding the transmitter as I am new to fox hunts.

What is the null, how is it used to find the transmitter? What does it do? Will it be a loud/quiet signal?

What is the peak, how is it used to find the transmitter? What does it do? Will it be a loud/quiet signal?

I do have an attenuator, too. Works with 4mhz steps.
Null=weakest. Peak =strongest. Use the "Null" with a loop and the "Peak" with a beam antenna. A loop is best (the Arrow antennas are good). Also, get a good compass, determine a good way to know where your antenna is pointed (with a loop if you look along the loop to get a bearing, which is often easiest, you have to + or - 90 degrees) and learn about "magnetic declination". Practice on know stations. Best thing to use with the antenna is an SDR with AGC turned off and use the display NOT your ears.
 

KE5MC

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One point about the null is to use it when close to the fox. When close the peak may be as an example 100 degrees wide. Null as mentioned will be sharper and not overwhelmed by the strength of the fox in close.
 

Jhernan488

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Location
Arizona
Null = Weak or no signal
Peak = Strong or loudest signal

Think of the loop as a rolling wheel, taking/aiming you in the direction you want to go. The thing is, with a loop like that, when you hear/see the peak signal you need to know which direction. That can be done with a technique called body fade. Hold the loop in front of your body and slowly turn your body 360 degrees. Somewhere during that turn the signal will get stronger and weaker. If you need to, spin again and again. Once you find the stronger signal direction, move in that direction. How far is an unknown. That is the art of direction finding.

At some point when the signal is strong, no matter which way you turn, that is when you start using the step attenuator. Then start the process over again.

If a local club is putting on the hunt, ask ahead if you can ride along with someone. If it is on foot, see if someone will let you pair up so that you can watch and learn.

I figure there are web pages providing plenty of information, as well as video tutorials. No need for me to write out what others have already done. Still, you may have questions after reading or watching videos. Come back and ask, happy to help.
How do I find this out?

One source says: When the signal is so strong that you can't find the null, tune 5 or 10 KHz off frequency to put the signal into the skirts of the receiver's IF passband. If your hand-held is dual-band (144/440 MHz) and you are hunting on two meters, try tuning to the much weaker third harmonic of the signal in the 70 cm band.

How do I find the harmonic in different steps, like 1st, 2nd, and 3rd? (I have dual band)

Im guessing this is the same as using an attenuator?
May this be a better option?
Maybe use both techniques and learn from it?

I think everything is held off till this covid is done.

I am so determined to learn this; it drives me crazy to not be able to figure something out. Hahaha
 

KE5MC

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Using local busy repeaters in your area, put your setup together and play with pointing antenna in different directions and attenuator dial settings to get the information to come together with hands on experience. Hopefully you have a secluded area to do this in. You will present a very high dork factor... :)
There is an offset from the fox I have to program the radio for. It does make reference to MHz for an offset as I recall. Don't key the HT when the attenuator is connected.
Good Luck,
Mike

P.S. I just went to the Arrow website. Likely as you have an Arrow antenna you got the 4 Mhz Fox Hunt Offset Attenuator. Just add 4 MHz to the receive frequency you are DF'ing. Nice piece of equipment and works well. I used it on my first fox hunt and was the only person to find the fox before the fox battery died. Others were closing in, I was just a little faster.
P.P.S Serious editing of the first part of the post about resistive attenuators.
 
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vagrant

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Typically, the T-Hunt frequency is 146.565 MHz, but it can be different, or there may be multiple frequencies/transmitters even on different bands. Still, 146.565 MHz is more common than not.

Options on how to get a bearing when the signal is strong:
1. Tune off frequency slightly in either direction, it does not matter which. The farther you tune away from the signal frequency, the more attenuation you are introducing. Do not tune too far where you cannot see/hear the signal.

2. The third harmonic is 3X the hunt frequency which gives us 439.695 MHz. Using the third harmonic introduces a significant amount of attenuation. I forget how much, but you may lose the signal and need to use option #1 most of the time.

You are correct that performing both of these options may be needed to obtain a bearing. The more you practice, the better. I have learned to do both out of habit with #1 being the first choice as #2 may result in not getting a signal at all when too far away.

Okay, without having your own T-Hunt transmitter to test with, another way could be to use your local NOAA weather frequency. Tune to its main frequency and spin 360 while observing the signal strength. A signal strength meter is better than only "listening" to how loud/weak the audio is. That NOAA signal is usually massive, so you may need to tune off frequency right away. Thus, if your NOAA freq is 162.400 MHz, start tuning up to 162.405, 162.410, 162.415 until you no longer hear/see the signal. Then step it back one frequency step and spin around to get a bearing. As it is easy for you to find out where your local NOAA transmitter is, you can use that to confirm your bearing. Still, you need to learn about triangulation. Once you have your initial bearing, even if you know where the transmitter is, get in your car and drive a few miles and get another bearing. Then, get in your vehicle and do it again. Do the bearings all match up? Keep driving in the direction of the signal and testing using more and more attenuation by dialing off frequency.

Testing this way can be problematic if you have two or more local NOAA stations and as you tune away from one, you come up on the other. You need to find out that first for your area and offset tune in the other direction. Also, remember that the NOAA stations are typically transmitting significantly more watts and signal strength than you would experience for a T-Hunt.

Try the above and it will help you with the basics and understanding attenuation. You don't always need to use that loop antenna either. You can and should try using the antenna that came with your radio and use the body fade technique (360 turn) while holding the radio against or very near to your body. Basically, your body is attenuating the signal from behind you to some degree and provides directivity.

This stuff is the basics. You really need to master this and riding/walking along with someone that has experience will help. You'll use your gear and they'll use theirs. Its okay if you think the signal is coming from a different direction from them. Just go with their choice and once the hunt is over, analyze why your readings were different. Was there a large metal vehicle in the direction you thought the signal was coming from? That was a reflection of the signal, and not its true direction.

All of that basic understanding helps, but a knowledgeable fox can put on a very difficult hunt for even the most seasoned hunters. Again, pairing up with someone will help to prevent you from being discouraged as you start out on this. You'll also find out that some hunters you're paired up with, may be terrible.
 
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