detector stem

[Tim]

Hi Koala. Yes this backyard jobby could also be made 3 piece I s'pose. A slightly thinner bottom shaft and and intermediate made from 22.5mm ally would work. I think most carbon/plastic lower shafts are smaller than broomstick anyway. Would need a second flange bracket also- no big deal. The wingnut/bolts could also be below the shaft. Twist ferrules are neater, but a bit problematic for the diy'er and/or expensive/hard to source. The black coil pictured is just one layer pvc with the Cat5 coil zip-tied and angle brackets araldited on, but I will attempt to make 12-15mm plywood male and female formers to heat-press thinner(downpipe) pvc for a clamshell design with a flat top- brackets araldited, foam filled, and sealed/glued with neutral cure adhesive silicone. I envisage foam broccoli boxes/lids will be my foam source. Twisted Cat5 coils have proven to be "fast" on my PIs, have been my most successful and are cost effective. Also the styrofoam offcuts dissolved in acetone may make good "supa-glue" for potting wound enamel vlf/IB coils ?? Worth a try-I hope it doesn't dissolve the enamel.....
I have had good success shielding my BFO/IB coils with mylarised plastic powdered milk bags. Unearthed.
I am still absolutely astounded by the performance of my BFO-Talking Electronics circuit8, a shunt-fed Colpitts with 3x 56nf Mylar caps, BC547B. 23 turns of .25mm enamelled on 6 inch with milk packet shielding, bottom only. This is the only BFO/IB I have made so far that doesn't register the wave of a hand. 50 and 70khz from memory. It has a 10 turn 500R pot in the coil-only circuit for fine tuning. The paired 56nf's are switchable to paired 100nf's The transistor is taped to the AM radio for maximum signal. It was built a while back, so the cap values are from memory, and may be wrong.
I am adamant this beater/boat motor will find non-ferrous amongst ferrous where PI's and discriminators alike fear to tread.

[bobsuruncle]

hello everyone ..... I have completed a few different types of detector circuits , minipulse ( ongoing ) , tgsl ( working but lacks depth , coil inductance is hard to achieve but getting closer ),garys pi ( works really well but haven't ground tested yet ) and 2 surf pi 1.2 's .....this is where the problem lies. The surf pi is my favourite as they are so simple and stable , however on the second build I used upper part of an elbow crutch (aluminium) . when I switched it on after assembly a radio I had going about 5 metres away was picking up the oscillation (not so with the first one which is all pvc . also the second build is giving up to ground interference now. could this be the upper part of the stem acting as an antenna ,? if so no more aluminium crutches . the coil on this one is spiral wound speaker wire type , 30 winds of 24 awg twin. no shielding but in a properly made housing . hope someone can confirm whther I am on track or not ....cheers Dave.

[Tim]

My BFO and SurfPro were both made with polio crutch upper stems, and had no problems. Perhaps your second 1.2 has a solder bridge somewhere? Try it on a different/no stem-process of elimination. 30 winds from memory would be for an 8 inch coil(??). Maybe a couple too many if your coil's bigger. Too many winds=higher inductance. The Surf uses less than some others.
The radio picking up a frequency may depend on where the dial was set.
Any metal or electricity within cooee of your projects will effect sensitivity, performance and adjustment, so set up outside or even out of town.
Hopefully someone with more experience will chime in here bob. Cheers.

[bobsuruncle]

Thanks for the reply Tim , inductance is around 300mh , and its not really a problem as such its just the behavior of this build on ground . You may be right about the solder bridge , I will check the board tomorrow . The thing is I have never used metal in a stem before and this is the only situation where ive had this more or less inconsistent response. This could be a delay issue , things come to mind as I type . Again on the bridged board , this machine was operating perfectly on the test bench with the coil (same length lead as is ) ....not so sure its a short . This is the only build ive had this effect with . Cheers mate , ( Morgan , hey ......been a few years since I was there ....Adelaide boy originally )

[Tim]

Cheers Bob. I lashed out on a ML commander 10x5 for my SMPro (it is set up for a DD). Shortest delay setting is only just enough to cancel the red ground here. Next build (with an Oscope), I will change the pot/R value(s).. The best homebrew coil I made in the past was a twisted Cat5 network cable(can't remember turns no.), with un-earthed mylarised plastic (powdered milk packet) shield on the bottom. Currently I have a "Tuggle"style coil on the bench which is showing good promise for small gold.
I've moved on from the crutch stems now, and use 700mmx 25mm aluminium from the hardware shop, 900mm laminated bamboo broomstick lower, and pvc fittings made from heatgun shaped sewer pipe. A cheap,light, compact, and super-strong design.

[homefire]

You can just buy the hard parts to make off the shelf. https://www.seriousdetecting.com/pro...tegory/shafts/



This would work for anything I would need.