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Frequency Changing and Hunting Together??
- Thread starter Canewrap
- Start date
tony (Orlando FL)
New member
I was detecting with my F70 along side a F75 and no problems unless the coils were about a ft apart. Seems to work well.
jackintexas
New member
In a competion hunt and it . seems there are no more targets. Everyone is walking around looking but few digging. After the hunt when 2 or 3 hunters go back there are quiet a few targets found. A lot of interference but it is not heard during the hunt....Jack
Ok, then it begs the question. What use is the frequency shift function on these machines or on some of the other brands (like Tesoros)? I have a hunting partner that uses an MXT and I have used an MXT and we usually have to be about 15 or so feet apart not to affect each other. I'm getting an F-70 and it sounds like we're still going to have hunt far apart and somebody has to shutoff his machine if we come together to check a signal. If what you're saying is true about the non noticed interference, then this feature is really a waste. However, with the argument that ensued after I asked my question, I wonder if anybody really understands this? Is there an EE in this crowd?
BarnacleBill
New member
Here's a couple of lifted paragraphs that are very general in nature.
"For telecommunications, desensitization is a form of electromagnetic interference where a radio receiver is unable to receive the full strength of a radio signal. This is caused by a nearby transmitter with a strong signal on a close frequency, which overloads the receiver and makes it unable to fully receive the desired signal."
"Receiver desense and transmitter noise generally go hand in hand - if you have one, it is likely that you will have the other. Receiver desense is caused by a strong off-frequency signal that is swamping or overloading the receiver - usually in the front end. Such a strong signal will cause the receiver to become practically non-functional. In such a condition the receiver can hardly respond to any weak signals."
The cures are not magical and involve common sense.
1. Move the antennas apart or change orientation(polarization).
2. Reduce transmit power.
3. Filter or clean up spurious transmitter noise.
4. Improve receiver filtering.
5. Change frequency.
It's the last that is what the manufacturers provide for the detector operator to use as a tool besides moving further apart. In higher end radio equipment it is the receiver filtering that separates the men from the boys. While mechanical filters are still important there is a greater movement towards the use of DSP(Digital Signal Processing), whereby the equivalent of mechanical filters are created in software. That allows many types & stages of filters to be created giving a good deal of flexibility to the designers.
The F75 lists a choice from F1 to F7, with F4 being the center frequency @ 13KHz via a crystal oscillator. If the interference is caused by 60Hz power then there are certain harmonics that F1 thru F7 would be bad choices for the designer.
[attachment 95330 F75harm.gif]
If the interference is from another source including other detectors, the use of a crystal oscillator can make it difficult to pull the fundamental frequency very far from it's center. There's also the matter of how tightly the coil is centered and the same goes for the existing filtering. Having a tunable coil, DSP filtering, and a digitally synthesized oscillator can vastly improve the ability to deal with interference.
Therefore the changing of the frequency can make it more pleasant to detect by not hearing the chatter which is helpful. But it is no guarantee that the detector is not being desensitized, and I'm not aware of any studies/reports that show those effects like there is in the radio field.
HH
BarnacleBill
"For telecommunications, desensitization is a form of electromagnetic interference where a radio receiver is unable to receive the full strength of a radio signal. This is caused by a nearby transmitter with a strong signal on a close frequency, which overloads the receiver and makes it unable to fully receive the desired signal."
"Receiver desense and transmitter noise generally go hand in hand - if you have one, it is likely that you will have the other. Receiver desense is caused by a strong off-frequency signal that is swamping or overloading the receiver - usually in the front end. Such a strong signal will cause the receiver to become practically non-functional. In such a condition the receiver can hardly respond to any weak signals."
The cures are not magical and involve common sense.
1. Move the antennas apart or change orientation(polarization).
2. Reduce transmit power.
3. Filter or clean up spurious transmitter noise.
4. Improve receiver filtering.
5. Change frequency.
It's the last that is what the manufacturers provide for the detector operator to use as a tool besides moving further apart. In higher end radio equipment it is the receiver filtering that separates the men from the boys. While mechanical filters are still important there is a greater movement towards the use of DSP(Digital Signal Processing), whereby the equivalent of mechanical filters are created in software. That allows many types & stages of filters to be created giving a good deal of flexibility to the designers.
The F75 lists a choice from F1 to F7, with F4 being the center frequency @ 13KHz via a crystal oscillator. If the interference is caused by 60Hz power then there are certain harmonics that F1 thru F7 would be bad choices for the designer.
[attachment 95330 F75harm.gif]
If the interference is from another source including other detectors, the use of a crystal oscillator can make it difficult to pull the fundamental frequency very far from it's center. There's also the matter of how tightly the coil is centered and the same goes for the existing filtering. Having a tunable coil, DSP filtering, and a digitally synthesized oscillator can vastly improve the ability to deal with interference.
Therefore the changing of the frequency can make it more pleasant to detect by not hearing the chatter which is helpful. But it is no guarantee that the detector is not being desensitized, and I'm not aware of any studies/reports that show those effects like there is in the radio field.
HH
BarnacleBill
Jackpine Savage
Active member
n/t
BuckeyeBrad
New member
n/t
vlad
Well-known member
DSP is no magic cure all or end all for all problems; many detectors including Eric Foster's Gold Scan still uses
analog because his words were, " I can get just as good results, and there are some definite advantages to staying
analog..." though he did not list them. What I suspect is more important is separate filters for both the transmit &
receiver sections, or for multi channels of TR's. As to the harmonics chosen by Dave Johnson for interference, I strongly suspect
some could be for other than 60 cycle or 120 volt, namely 220, 440 volt and general RFI or ground minerals or salt.
Plus the fact that someone might be hunting beside another F-75 user or detector.
The whole point I made was that it was just a slight bleed-off from the main frequency when you frequency shift. Using
a quartz crystal precludes major shift changes-the whole point being to lock in to a certain frequency and not drift.
Having a tunable coil? The coil is tuned to the one specific detector/frequency, with an exception already noted.
"Digitally synthesized"-is a fancy way of saying produced or made, and you can have digital oscillators that are
poorly designed and shielded; digital does not assure quality, any more than analog infers inferior design or
shielding. While " tunable coil ....digitally synthesized oscillator..." may improve, it may not, also.
As to studies in the radio field, I'm not aware of any about CONSTANT WAVE electronics that TRANSMIT AND
RECEIVE AT THE SAME TIME.
analog because his words were, " I can get just as good results, and there are some definite advantages to staying
analog..." though he did not list them. What I suspect is more important is separate filters for both the transmit &
receiver sections, or for multi channels of TR's. As to the harmonics chosen by Dave Johnson for interference, I strongly suspect
some could be for other than 60 cycle or 120 volt, namely 220, 440 volt and general RFI or ground minerals or salt.
Plus the fact that someone might be hunting beside another F-75 user or detector.
The whole point I made was that it was just a slight bleed-off from the main frequency when you frequency shift. Using
a quartz crystal precludes major shift changes-the whole point being to lock in to a certain frequency and not drift.
Having a tunable coil? The coil is tuned to the one specific detector/frequency, with an exception already noted.
"Digitally synthesized"-is a fancy way of saying produced or made, and you can have digital oscillators that are
poorly designed and shielded; digital does not assure quality, any more than analog infers inferior design or
shielding. While " tunable coil ....digitally synthesized oscillator..." may improve, it may not, also.
As to studies in the radio field, I'm not aware of any about CONSTANT WAVE electronics that TRANSMIT AND
RECEIVE AT THE SAME TIME.
John in Florida
Well-known member
You are exactly correct.