f70 chatter "freqed-out"

[IBdiggin]

Actually I did not know they didn't make a 5x8 DD for the F70. But strange this conversation came up because I asked the dealer when I bought mine how performance of the 10" concentric compared to the DD on the F5 he had right beside the 70 on the bench. He said well "lets see" and did the last thing I thought I would see. He crossed the connection cable over from the F5 TO THE f70 and it worked. Actually preformed an air test with all his samples he has taped to his paint sticks and the F70 actually did as well if not a little better than the F5 with the same coil. What is with that?

 

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[steve1357]

Well....

The coil is an "antenna", matched by impedance along with frequency. Any coil will "work" (as long as the wiring matches) just as any antenna will work. ( a coat hanger will work on your TV) But unless the antenna is matched, you won't see peak performance. Woof (Dave Johnson-Fisher) has several posts about swapping coils around, basically not a good idea, I don't think his comments are driven by revenue. The T2 and F70/F75 are both 13khz but the coils are incompatible. Then again the Greek series of Teknetics coils are compatible with the G2 and GoldBug Pro even though they are far different frequencies. (My memory may be off, so due your own research before you blow something up!)

How much of a mismatch/loss you'll see from using the F5 coil on the F70 I don't know. Or how the frequency difference will affect the radiation pattern/target separation.

The F70 is deeper than my F5 by several inches. Fisher has a 6.5" coil for the F70 but it's not a DD. The 5" is DD.

 

[steve1357]

Ok, now I'm curious. Do you like both coils for their own abilities or do you have a one over the other preference? I still have only the 10" concentric. I am still trying to decide if the F70 is enough like the F5 to consider Mike H. recommendation of the 5"x8" DD he refers to in his writings about the F5. I did find a nice clean volleyball court yesterday and was able to run in sl mode at a mildly chatty sensitivity of 75 and 0 disc. and 0 threshold. WOW, I was impressed with the increase of depth. No bling but over $5.oo in clad.----HH

Got out this afternoon with the F5 and F70 and my extra coils for each. I used the match coil for the detector, my F5 is an older push in type, but the F5 5" DD coil is the new type.

My findings in my garden, ground balance around 60, your mileage may vary....

On both the F5 and F70, the 5" DD isn't that far behind the stock 10" non-DD when it comes to depth. I was surprised. An inch less, 2 at the most when looking at 7" on the F5 and 9" on the F70.

I don't have a 11" DD for the F5, but changing from the 10" stock to the 11" DD on the F70 was a huge difference, four or more inches? I have a quarter buried at 10" that only the F70 with 11DD running all metal and SL mode can find with a solid, repeatable signal. The F5 can't find a quarter at 8" with either coil, the F70 can get it on DE and running discrimination, though it's on the edge running DE. You can ground balance the F5 on top of the 10" deep quarter and no indication something is there compared to nearby clear ground, while the F70 ground balance will change from 60 to 55 or 57.

I ordered the F70 with 11"DD coil, I wasted money getting the 10" stock coil. I never use the 10", I'm either in clean ground running the 11DD or coin shooting in between tabs with the 5DD on the F70.

I guess to sum up, I use the 5"DD and 11"DD coils all the time. I got the 10" stock to see if it would settle down my initial problems I was having. I don't think about the theory of covering more ground with a football coil like a 6.5 or the 5x8, I use the 11" if I can, I use the 5" when it's crowded.

Unless Dave or someone else weighs in, I'd venture to guess an F70 tuned 5" DD coil on the F70 will outperform, on depth, the F5 5x8 coil mismatched on the F70. Does your dealer have a F70/F75 5"DD coil you could bring in your F70 and try?

 

[IBdiggin]

That's what startled me when he screwed that F5 coil onto the F70. I had 10 and 11 meter radio when I was younger. An incorrect standing wave would actually fry the finals in a radio if the mismatch was severe enough. That's why the transmitters were tunable because of the width of the attainable frequency band. So not knowing what to expect when he turned the detector on was a little startling. I'm surprised the connectors are even compatible. I do not know if he has extra coils on hand but I would probably order on line anyway. Save the tax and the trip of 40 miles.

 

[steve1357]

You are correct.

With metal detectors, I assume with the low levels involved, even if the impedance is a complete mismatch, the levels do not exceed ratings of the circuitry involved.

Be aware, one issue I had that Rick at Fisher resolved immediately, they changed up the housing of the 5" DD coils a little to where the common 5" coil cover you see won't fit; the new coil is a tad larger and has ribs on it now for the new cover to easily snap on and off. I received the old cover and the new coil, Rick sent me the new cover quickly. Awesome service. I mention it as I see several online dealers still only list the original cover yet show pictures of the new coil.

Get the 5"DD and clean up the Tiki bar, then return after summer with a 11"DD, a friend, and a shovel.