I have an AT Pro as well and was thinking about getting the smaller coil for it.

Hay Leo, I worked 0ver 30 years in electronics so we both look deeper into the detector functions than most.  You nailed the functions fairly well. I did some work in sat receivers, but most of my work was in control circuits. I think you were dead on in the frequency comment. The Navy is the only one I know that is using 2 Hz for communications with subs and the new sats have gone beyond anything I worked on.   In my comments, what I was trying to get across is that I go for the 'average best size' coil and never change it. I have found everything from pickers to boat anchors with the 9.5" stock coils on my Whites detectors.  Cache hunting is a different story. I have found caches at 6' with my old Hays 2 Box. The 90 degree phase offset and the large spacing between coils gives it the depth.  Here's a crazy thing about the Hays. The metal trim on the cases are actually the coils!

Hay, maybe I am just lazy and just use the stock coils so I don't have to change them. lol , But I think they have found just about every type of object that be found. Happy hunting,  Frank...-

Thanks Frank. See that is my confusion as well when it comes to coils. I see quite a bit written about them and see many questions being asked. And if someone's electronic knowledge goes no further than replacing batteries in the detector, it could be worse for them trying to comprehend it all. Late 2013 I bought a Whites TLD pro and it has 2 stock coils. Right away I started thinking if I should replace them or not for something that will give me better performance. But...I only used it twice, so I am going to forget that idea. Why don't someone make "high" powered detector's to really punch through the ground. Well I know PI machines do that but how about VLF's. Maybe there are limitations by the FCC as to how much power one can put out before it is classified as a "broadcasting station" or require a permit to operate! I am hoping to get out to Nevada this month and learn more of it.

Well I usually hangout in Reno and Lovelock area and I don't notice the heat that much. I actually like it.  I think its much more tolerable than what we have in Miami with humidity.

I wouldnt want to be in Arizona though in summer, that is extreme!

Leo, you sound like one of the snowbirds. I stopped by Stanton a few years back and talked with some of the LDMA  members. They said they were heading north before summer hit there.  I am in Good Sam and LOW and travel in a small MH. I use for a base camp when I prospect or cache hunt. This was taken near Stanton.  Frank...-

 Hay, 4 wheel drive and 305 Diesel ponies. I went down some of the jeep trails.

I  Leo, I use to tow a dune buggy, 64VW chassis and &74 Engine, but it needs some repairs so it is sitting in my yard. I found I really didn't need it most of the time since I could get in the center of most claims with the MH. It is only 21' long and is essentially a Ram HD truck beefed up to 12K # capacity. it is an ideal base camp. All the comforts of home in the boonies. Queen size bed for the old back and fresh coffee to wake me in the morning.  It's an '05 MH but it is built to last. Aluminum floor and welded frame with a one peace fiberglass shell. Air bags in the rear and 4 wheel drive.  It will probably outlast me. lol  It has been Maryland to West coast several times.  I am mostly a cache hunter, but I fill in with prospecting on trips looking for caches.  I just spent a year researching one and trying to get permission to search the site, Finally got permission to hunt for the $50,000 in gold $20 coins. Spent 2 weeks searching with my Hayes 2 Box only to find two big holes under a big bolder on a hill side.   Well that makes my find ratio about 1 in 10. 

Good luck up in Nevada.   Frank...-

                                                               This was taken in Quartzite several years back.