The Crossbow Classic PI

[Golden_Boy]

Thank you very much Qiaozhi for the response, really appreciate it.I will order a kit from Silverdog and try to build the MPP detector. If I'm successful, will post pictures/video of the finished machine and some performance tests too.Thanks again for the opportunity to learn how to build a metal detector.

[Qiaozhi]

Hi to all members on this great forum,I`m new to the metal detecting hobby,but still i will try to build a metal detector for personal use,so pls don`t flame me if i
ask stupid questions,if someone can answer them i will be very grateful...

Here are the questions:

1.Which detector is better for relic and hoard hunting, the Crossbow Classic PI Rev.C or the MPP Beach REV-E ,where I live there are no beaches,so I will
never use it for beach combing or finding small gold nuggets,my main goal is finding deeply buried relics and coin caches.

Either detector can be used for relic and hoard hunting.

2.If the Crossbow Classic PI is better from the two,what exactly are the difficulties with the Rev.C PCB,I`ve read in some posts that there are some problems even with the last Rev.C,pls elaborate.

Crossbow Classic PI (CCPI) is a variant of Hammerhead, as is the Mirage. However, CCPI consisted of a short run of 13 machines, and some members of Sven's website have built their own. There are no PCBs available at this time. MPP Beach Rev-E would be a better option at the moment. Don't be confused by the word "Beach", as the settings are fully adjustable on this version. It is perfectly suitable for anything from small low conductivity items, up to very large targets. You can set up the detector as appropriate for your needs. Alternatively, have a look at Hammerhead -> http://www.geotech1.com/cgi-bin/page...head/index.dat

3.What were the coil parameters(inductance,capacitance,resistance, number of turns,wire gauge,type of wire,material used for coil shielding,value of damping
resistor etc...) on the original Crossbow machines,I want to build a 10" coil for now,later i will go with 1m coil.

For the record, the original coil was wound with 0.56mm enamelled copper wire for an inductance of (I think) 400uH. The electrostatic shielding was with 20um adhesive aluminium tape, and the damping resistor was 470R.

P.S. I know the Crossbow is not intended for beginners, but i will have some help from my buddie,he has a degree in electronics and the necessary test
equipment so there should be no problems.

P.P.S. Sorry for my bad English,its not my native tongue,I hope u understand...

In conclusion, your best bet would be the latest incarnation of MPP (Rev-E), as there are PCBs and kits available from Silverdog, and the design can be setup as you wish. It also has a 2-stage preamp, which is preferable to the single-stage preamp of CCPI.

[Golden_Boy]

Hi to all members on this great forum,I`m new to the metal detecting hobby,but still i will try to build a metal detector for personal use,so pls don`t flame me if i
ask stupid questions,if someone can answer them i will be very grateful...

Here are the questions:

1.Which detector is better for relic and hoard hunting, the Crossbow Classic PI Rev.C or the MPP Beach REV-E ,where I live there are no beaches,so I will
never use it for beach combing or finding small gold nuggets,my main goal is finding deeply buried relics and coin caches.

2.If the Crossbow Classic PI is better from the two,what exactly are the difficulties with the Rev.C PCB,I`ve read in some posts that there are some problems
even with the last Rev.C,pls elaborate.

3.What were the coil parameters(inductance,capacitance,resistance, number of turns,wire gauge,type of wire,material used for coil shielding,value of damping
resistor etc...) on the original Crossbow machines,I want to build a 10" coil for now,later i will go with 1m coil.

P.S. I know the Crossbow is not intended for beginners, but i will have some help from my buddie,he has a degree in electronics and the necessary test
equipment so there should be no problems.

P.P.S. Sorry for my bad English,its not my native tongue,I hope u understand...

[Tim]

Could be good for the mineralised ground. A long while back I tried a dual field arrangement from Cat5, but knowing very little about damping, balance or phase it wasn't successful. I have too many projects on the go to start another at this stage. Cheers.

[Qiaozhi]

George would it be possible for you to draw a diagram of this coil arrangement?? TIA.

I don't have a diagram, as the measurements were made at the coil plug. Basically there appears to be 2 coils in a DD configuration (actually they call it a butterfly) which are in series and connected to the detector as a mono coil. I don't know whether these are in anti-phase or not, but I suspect that's the case. The coil with the largest inductance is the one that's connected to the screen. The damping resistor goes across the two coils. If I can find time to build and experiment with this configuration, I'll let you know the result.

[Tim]

It turns out that the Detech SEF coil is rather unusual.


The coil plug wiring is as follows:
L1 263uH (6R6) coil between pins 1 and 2
L2 706uH (7R0) between pins 2 and 3
pins 1 and 5 connected together
pins 3 and 4 connected together

Obviously, with pins 1 and 5 shorted together, the coil plug wiring is connecting the coil as a mono with L1 and L2 in series. Effectively this means the detector "sees" a mono coil with 439uH, requiring a 330R damping resistor between pins 4 and 5.
What's interesting is that a mono coil is sensitive from edge to edge, whereas the SEF coil is sensitive across the overlapping section of the two loops. Hence it reacts like a DD coil, but with the advantages of a mono.

In a way, this setup is similar to a White's Dual Field, but in a Butterfly (DD) format. Although, in this case, it was possible to critically damp the coil with one resistor.

George would it be possible for you to draw a diagram of this coil arrangement?? TIA.

[Qiaozhi]

Hi thank you for your speedy reply. I wasn't asking you to do the project build l was asking your permission for me to attempt a biuld.

Yes, of course, if you want to build one for yourself, then go ahead. Others from Sven's site have managed to do so.

[wayne,inspain]

Hi thank you for your speedy reply. I wasn't asking you to do the project build l was asking your permission for me to attempt a biuld.

[Qiaozhi]

Hi, this is my first post here, I have been reading about the crossbow classic and wondered if it would be ok to do a project build here. I believe that the administrator designed and manufactured 13 and they are much sort after and I can understand if he wants to keep them exclusive.

At the moment I do not have the time available to create and maintain a project build for the Crossbow. Also, it would be a particularly tricky project for most people.

However (spoiler alert!) there is a new version of the Minipulse Plus which will be made available in the next few weeks, that is intended for use on the beach. Surpisingly this will be called "MPP Beach", and will have similar performance to the Crossbow. This version was intended to be released as an "end of year" present to the forum, but I was unfortunately struck down with the dreaded flu that lingered on for several weeks. The Build Document still needs to be completed, but Silverdog will be making kits and PCBs available as soon as that's completed. I cannot give you a accurate release date just yet, so please keep an eye out.

[wayne,inspain]

Hi, this is my first post here, I have been reading about the crossbow classic and wondered if it would be ok to do a project build here. I believe that the administrator designed and manufactured 13 and they are much sort after and I can understand if he wants to keep them exclusive.

[6666]

https://youtu.be/RWgHZM3RahQ
https://youtu.be/V0ZZN45r2sc

thanks, works very good.

[Carlos]

https://youtu.be/RWgHZM3RahQ

https://youtu.be/V0ZZN45r2sc

[kt315]

In my detector i put 1k x 2w and remplaced for the IRF740.
I see in my scope the curve of decay the wave (see my photos)

open Moreland's article on Hammerhead PI and look page 15 figures 24, 25 etc.
you have to get same signal.

[Carlos]

hello, yes I have but with a search coil of 23 cm. I already sent the link. with the search coil of 45 cm. increases the sensitivity of the objects by 30%. An aluminum can of 330cc with the small one detects it between 60 to 65 cm. and with the large one at 80 to 85 cm.

[6666]

This is my search coil 45 cm. 13 turns telephone wire 235 uH.

nice coil, carlos do you have any video of your detector working ?