Fisher F-75

[Goodrat]

OK, who has one? Does this machine have negative pulses?

[Carl-NC]

Negative pulses? What do you mean?

[Goodrat]

Negative

Hi Carl.
Fishers usually have the tip as positive, the ring as ground and the sleeve not used. However some machines have the pulse in a negative polatity at the tip. I have a customer that has no output on his F-75 on a headphone model I used to make that has a diode in series (it has a circuit that allows you to vary the tone to the speakers).
So I'm trying to gather info on the F-75.

[ivconic]

.....

.....Although respect Fisher much, i dont like panels like this!
To much playing through menus.....
Reminds me on cell phone...
Anyway i do beleive it is hell of a machine...
Looking forward for some tests...
Regards!

[ivconic]

.....

Carl i want to post photos here to be seen! Like it was in the past...
Why the hell is not like it was before?

Now i have to post 2 posts separate to see photos here....
Shhheeeeeeeeeeeeeeeesh!!!!
Anyway...regards!

[ivconic]

....

Numero 2...

[J_Player]

The F-75 us unlike the other Fisher detectors. Fisher bought Technetics and made improvements on their top model, the T2, calling it the F75. The F75 is basically a Technetics T2 with extra bells and whistles, as well as a claimed slight improvement in detecting strength. The Audio output will work with any standard headphones. All the signal processing is done before the audio stage, so the audio does not have large +/- voltage swings depending on a target.

.....Although respect Fisher much, i dont like panels like this!
To much playing through menus.....
Reminds me on cell phone...
Anyway i do beleive it is hell of a machine...
Looking forward for some tests..

I own a Technetics T2, I agree the F75 has tons of menus. What I have discovered is that most of the menus on the F75 as well as the T2 are for making adjustments in the discriminating mode, and I rarely use this mode. In the all-metal mode, these detectors show a visual ID of the target on the screen. When switching to discriminating mode, the electronics simply filters out some of the targets so they do not appear on the headphones or screen. All the menus are concerned with details of filtering and discriminating different signals. In addition to regular discrimination, the F75 has several hunting modes of factory preset discrimination settings, and it is also capable of filtering in an adjustable notch mode so you only see a narrow band of targets.

The problem with this discriminating scheme is that many good targets are lost, as the T-2/F75 target ID is not perfect. I have found that I get the best targets by using headphones to hear the sounds and also look at the target ID on the screen in the all metal mode. Then I can decide what targets to dig rather than have some of the targets hidden from me by the electronics. The target ID errors I found on the T2 are usually in areas where I am hunting for coins and jewelry in damp beach sand with pockets of black sand. I have found old, corroded coins that can signal anywhere on the scale from iron to quarters. Gold rings which usually signal similar to a US nickel sometimes signal high in the penny/dime range. I found a cubic zirconium ear ring with a steel post that signaled as a very low iron object, bordering on a hot rock. In these difficult hunting conditions, I usually listen for a stable, repeatable signal as I sweep the target from several directions, and about half the time the target ID turns out to be incorrect after I dig up the target to see. This is why I rarely use the discriminating feature. This detector is by far my favorite all around coin/relic hunter because it is so sensitive, and it is the most lightweight I have used. I find the T2 is about 80% accurate for target ID In regular soil, and I use the discrimination only in very trashy parks to eliminate the aluminum foil and iron. Here is a link to a post I made that illustrates the kind of targets I found with the T2 in difficult black sand: http://www.thetreasuredepot.com/cgi-....pl?read=95198

While the F75 has over twice as many menus as the T2 for the discriminating mode, the all-metal mode is still simple like on the T2. For those who like discriminating mode, the menus are actually not that hard to figure out. there is about a 2 week learning curve. The advantages of the F75 that appeal to me over the T2 are: back-lit screen, non-volatile memory remembers how you last set the detector, and possibly better target-sensing (some user reports say the T2 actually detects deeper, while others say the F75 does).

What I like about both the T2 and the F75 is:
Very deep and sensitive - able to locate coins and jewelry next to trash
very lightweight - I can swing it all day long and never tired arm
Runs for about 40 hours on 4 alkaline AA cells.
Only 3 things to set in the all-metal mode, also a 1-second auto ground balance feature.
Will hunt well in damp saltwater sand. When hunting in wet or submerged sand, the depth and target ID is diminished a lot.

What I don't like:
If you bump the battery compartment there is a good chance the power will temporarily interrupt, so you need to set up the detector again. On the F75, it remembers your last settings, so all you need to do is ground balance after losing power.
No back-lit display (T2 only).

What I don't care about:
Discrimination menus that only clog up the panel face and do not add any detecting ability. I guess it doesn't hurt anything to have it there if you don't use it.

[Goodrat]

T2

So maybe someone can hook up a T2 phone output to a scope? I'd like to know the output wiring/polarity and maybe peak output voltage no load, peak with known load (to calculate the output impedance), highest duty cycle.
I wish the manufactures would actually put specs in their specs. That would be nice!

[Goodrat]

I called Fisher...

I just got off the phone with Fisher.
The line in the manual "Mono headphones will not work" is not accurate. It should read "Headphones with a mono plug will not work".
Inside the machine, the tip and ring are shorted together and the sleeve is ground. This is a mono output, but a mono plug would short the output. Also the output impedance of the F-75 is 274 ohms with a peak of 6 volts (no load). Highest duty cycle is 25%.

[Goodrat]

Negative

Oh, and the pulses are negative with respect to ground.
Must have old engineers