Rx recommendations for SEF coils on the V3

[ramases]

Hi All

This is a question really aimed at existing V3 SEF coil users - especially the 10X12. What sort of Rx recommendation do you get with the Probe feature? I have one coming (not V-rated) but have read elsewhere that the recommended Rx tends to be very low (in low single figures). Of course I know that Rx is not everything as SEFs have other advantages, but I would be interested to know what Rx you get from your SEF against the recommendation for the 10" DD or 6X10, assuming all other settings remain the same. Finally, now that some time has passed, how are folks doing with SEFs on the V3?

Cheers.

Colin.

 

[slumpshooter]

I use several SEF coils the Butter fly and the 5" coil, both are DD. The Rx recommendations are lower than with the White 10" DD 2 when running all 3 frequencies, but do run generally higher when running a single frequency, ether 2.5 or 7.5 Khz, no overload even on TX boost, However the Rx gains start to drop when running single freq. on 22.5 and little more susceptible to overload under certain circumstances.

 

[Rob (IL)]

All are made by DeTech but the 5" is a DD not a SEF. The suggested RX gain is a misunderstood feature and I'm not going into it . I have hunted with Larry and he ran the 10x12 with great success. This has already been posted. In most cases the suggested RX gain will be lower because of the 22.5 frequency. The suggested gain should have be left off the V. What is important is to run it keeping the signal loss to a reasonable level. Remember the suggested gain is based on 10% which is pretty low. I would suggest staying below 50%. Rob

 

[slumpshooter]

Colin, I think Rob is right about the gain concerns (not to big a deal) and he is also correct that the 5" DD is not SEF. I guess my point was to try and point out that with some freq. that other coils can work and that using all three freq. (mainly the 22.5) it starts to get dicey, but I am sure that has been posted before here.

 

[ramases]

You're beginning to confirm a lot of what I have been thinking. 22.5KHz seems to be the main issue for a non-V-rated SEF as it seems that at this frequency the lack of a deep null has a significant effect on recommended Rx. I have seen other posts that suggest that the 10% noise "allowance" is not an absolute "limit" - to my mind it is just "stability" that is the real issue. I have a mate who has been very worried about the low Rx recommendation he has been getting with his SEF compared to his other coils. I have suggested running with 7.5KHz (not ideal for our tiny, thin hammered silver coins) if it is bothering him so much, and the above posts seem to confirm this. Thanks all for your input.... I'd welcome any further suggestions and observations and will let you all know how I get on with mine when it arrives.

 

[TheMarshall]

All are made by DeTech but the 5" is a DD not a SEF. The suggested RX gain is a misunderstood feature and I'm not going into it . I have hunted with Larry and he ran the 10x12 with great success. This has already been posted. In most cases the suggested RX gain will be lower because of the 22.5 frequency. The suggested gain should have be left off the V. What is important is to run it keeping the signal loss to a reasonable level. Remember the suggested gain is based on 10% which is pretty low. I would suggest staying below 50%. Rob

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Hello rc.........Are you understanding matters correctly?


I ask because of this part of your post:- ' the 5" is a DD not a SEF '


and.............................................The suggested gain should have be left off the V. What is important is to run it keeping the signal loss to a reasonable level.

...................................................Remember the suggested gain is based on 10% which is pretty low. I would suggest staying below 50%. Rob

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Now a question to Larry. Why isn't a proffessional assesment made of the suitability of such coils, for use on the Whites V3?

 

[Rob (IL)]

Hello rc.........Are you understanding matters correctly?
I think so.


I ask because of this part of your post:- ' the 5" is a DD not a SEF '
The 5" is a DD and not an SEF (symmetrical electro magetic field) anymore than an OO coil is a DD.

[attachment 154114 coil.jpg]


and.............................................The suggested gain should have be left off the V. What is important is to run it keeping the signal loss to a reasonable level.

No be surprised. The suggested gain is used wrongly by more people and it is used correctly. Most of us who are using our V's correctly don't bother with it. What good is it? Does it tell you if your coil is good, NO. Does it tell you how high you can run your gain, NO. Does it help get deeper , No. So what good is it?

...................................................Remember the suggested gain is based on 10% which is pretty low. I would suggest staying below 50%.\
This a quote by Carl at Whites.
Rob

 

[Larry (IL)]

I think suitability would vary so much on what ground conditions are that it would be very hard to give a professional assessment that would apply to all.

 

[Larry (IL)]

The recommended RX is just another tool to use if you prefer to use it IMHO. I don't pay a lot of attention to the RX, I would rather have stability than High gain. It would seem to me that a high gain coil with higher losses and more noise would not be a better choice than a lower RX coil with less noise and losses, IN MY GROUND, anyway. Your ground and hunting style may change what coil would be best for you. What I tell hunters when asked what coil is best, is try as many as you can and sell the ones you don't like and keep the ones that work for you.

I have asked Carl for his input here.....lets see what he says too.

 

[slumpshooter]

What I tell hunters when asked what coil is best, is try as many as you can and sell the ones you don't like and keep the ones that work for you.

Great advise Larry, Thank you!

 

[Carl-NC]

Not sure what you mean by "high loss" and "low loss". Three things can limit the gain: EMI, ground mineralization, and loop null. EMI shows up as chatter. Ground & loop null combine to cause overload or make GB difficult. These are true for any IB detector. None of these are losses, but rather they reduce the available dynamic range. With EMI, the reduction is on the low end (minimum detectable signal), with ground+null the reduction is on the high end (large/shallow target overload).

The bottom line is, with any coil, run the gain as high as you can for stable operation, just as you'd do with any detector.

Regarding the use of SEF coils on V3, White's makes no official assessment of the suitability or performance of aftermarket accessories. However, aftermarket loops not specifically made for V3 will struggle a bit, especially at 22.5kHz, both with gain setting and with VDI accuracy. Even so, I've found the aftermarket loops I've tried -- Bigfoot, SEF, and Sunray -- to be very usable.

- Carl

 

[Larry (IL)]

By high or low loss, I am referring to the Sensitivity Probe % of signal lost by having the RX too high or a lower setting then the suggested setting of the V3. Some users are known to up the RX Gain even though the signal loss is 50% or more. While others will lower the RX Gain to keep the signal loss to 10% or less.

 

[Carl-NC]

Sens. probe doesn't indicate signal "loss", but rather the amount of residual signal present. If ground+null are the cause, then this doesn't take away from sensitivity. Instead, it takes away from large/shallow target response, manifested in signal overload. If you are hunting in a clean area with only deep targets, then run the gain just below the overload point for max depth. But if there are a lot of shallow targets, then this will result in a lot of audio overload signals which might be annoying.

- Carl

 

[Larry (IL)]

That is a good explanation Carl. The example given on page 33 of the owners manual, Sensitivity/Probe/Examples/ says that is the % of transmitted signal that is lost. Although I never did understand why increasing the RX Gain would result in higher TX loss.