Mike,
Just thought I would jump in with a few observations to your post and some comments. First, let's review your post:
<STRONG>"Awhile back I asked about the MXT for Prospecting and Jim McCulloch stated that the MXT could find flakes as small as 1/4 of a grain. Is that because the MXT runs on 14.7 kilohertz(khz)?"</STRONG>... Actually, the MXT operates at <EM>about</EM> 14 kHz. The primary design engineer, David Johnson, states the operating frequency is 13.889 kHz. As for the responsiveness to small sized gold, yes, <EM>part</EM> of the reason can be attributed to the operating frequency.
<STRONG>"I'm trying to understand the relationship between khz and sensitivity."</STRONG>.... There can be some relationship between operating frequency and responsiveness to small and/or low conductive targets, such as gold jewelry or US 5¢ coins, as well as performance on higher-conductive silver or copper coinage. You also have to factor in the detector's ability to handle ground signal, especially in highly mineralized environments, and that calls for an understanding of not just the operating frequency, but also the filtering used to process ground signals Vs target signals. And let me just offer the reminder that nothing is 'perfect' when it comes to detector operation. There is textbook <EM>theory,</EM> and then there is actual <EM>in-the-field-performance</EM>. The two do not always agree!
<STRONG>"If kilohertz is the determining factor for sensitivity to small gold then how will the Whites Beach Hunter ID work for gold? I would really like a detector for wet sand beach hunting and Prospecting. Will the Beach Hunter ID fill the bill?"</STRONG>.... The Beachhunter ID might work with similar frequencies to the DFX, but lacks some of the DFX's refinemnents and other adjustsment functions. Thus, it can't really be compared. It is mainly waterproof. I wouldn't consider it a candidate for the tasks your mentioned.
<STRONG>"If not what is the differnece between the 15khz the MXT has and the 15khz the Beach Hunter ID has? For that matter the DFX also has 15khz."</STRONG>.... Again, just to clarify, the MXT operates at 13.889 kHz, and the DFX's designer stated the 3 kHz & 15 kHz are actually 2.98 kHz and 14.91 kHz.
Let's look at how operating frequency and target sensitivity <EM>generally</EM> tend to be associated. As a rule, it has been determined that detectors operating at the lower-end of the VLF range, such as about 3 kHz, have better sensitivity and discriminating ability on higher-conductive targets that would be in the zinc cent through silver dollar range. They also do a much better job of handling and penetrating more mineralized ground.
Detectors that operate more in the upper-end of the VLF range, such as those at about 14 kHz to 15 kHz, tend to be more responsive to smaller targets and/or those of a lower-conductivity value, such as foil through US 5¢ range. The downside is that they perform best in lower mineralized environments.
<STRONG>"Are all three equal when it comes to finding Gold? If not Why?"</STRONG>.... No, not really. The DFX does provide the ability for the operator to select the 15 kHz operating frequency ONLY, and then make adjustments to get the most out of it. For some nugget hunting applications, this can be 'OK.' The operating frequency will be fine for responsiveness to gold nuggets, but it lacks the bad ground handling ability and punch of the lower-frequency. This can make it a bit squirrely in high mineralized environments, too.
<STRONG>"Sorry for all the questions. I'm trying to understand what makes three detectors with equal khz not be good for the same kind of hunting."</STRONG>.... The DFX, like the XLT, was designed with factory preset programs so operators could select a program that could be used for various applications, such as the "Prospecting" mode. However, that doesn't mean that the particular detector is designed for very serious use for that application.
Ground handling ability is also an important consideration and here is where we have to take a harder look at the MXT. The MXT was a model still in the R&D stage when the DFX was released. The MXT is an off-shoot project of the GMT. The Gold Master Tracker (GMT) operates at that higher operating frequency, not usually associated with very good ground penetration, but noted for responsiveness to smaller and/or low-conductive targets. The MXT had some design changes so that it would work at a frequency in closer association with the DFX and be able to utilize the search coils available for the DFX.
The DFX, even with all the adjustment features, is still basically a moderate-to-faster sweep design, more like the XL Pro and XLT, than is the MXT, which is a two-filter design. The MXT was <EM>designed</EM> for better operation in the Prospecting mode because it was derived from the strain of a gold prospecting unit. It's AutoTrac® circuitry is very different from that of the DFX or XLT or XL Pro, and what is also interesting si that even though the DFX has a vast array of adjustment features, it can NOT be set up to dupliate the performance of the MXT. Maybe to be somewhat similar in some ways, but not able to duplicate it.
So a short and simple answer to your last questions is that, regardless of the fact that the DFX, BeachHunter ID and MXT might all operate at somewhat similar frequencies, all the rest of the circuitry was not designed to operate the same way.
Let me insert one more observation of different performance from same-frequency models. I will take an XLT, XL Pro and Classic (III, ID, IDX Pro) which all operate at about 6.59 kHz.
Through this past decade that the XLT has been out, I have read or had comments made, many times, about the XLT's poor performance on the US nickel (5¢) coin. Often people have said their nickel count was low compared with some people using a Tesoro, for example, that operated at a higher frequency.
My immediate questions were <EM>"Do you hunt with Tone ID 'ON'?"</EM> and <EM>"What program and discriminate setting are you using?</EM> Almost 100% said they did use Tone ID, and most were using a program, factory or custom, that had too much discrimination. I suggested they turn Tone ID 'Off' and open up the discrimination, then hunt for a few months. In most cases, those who were able to do so (patience to not use Tone ID) found that they had much better nickel counts. The responsiveness on lower-conductive targets, such as nickels and gold jewelry, was very improved, and especially the initial 'Hit' you get when you sweep over a nickel or other target w/o Tone ID in use.
In contrast, many of those using an XL Pro can do quite well on US nickels but that's partly because they do not have a Tone ID function to impact the detector's performance, nor do they have any notching. Most XL Pro operators seem to hunt with a minimum of discrimination and a 5¢ coin hits quite well.
Then there is the excellent Classic series. Retailing for about ½ or less the price of an XLT, and definitely lacking the myriad of adjuistsment features, these nifty 2-filter, silent-search, quick-response models can hit quite well on a nickel coin!
Same frequency, but different circuitry and operatuing charastics. There just isn't a "perfect" detector out there. Some of us perfer to have two, or three, or more detectors in our arsenal to take advantages of their strengths. Many in the hobby, however, are only able to justify one detector and thuis they have to do their homework in order to select the best one that will fit their needs. If you want to hunt coins, relics, and still have excellent gold jewlery performance <EM>and</EM> a very worthy gold nugget hunting detector, the MXT is certainly about the best choice you could make.
As for "wet sand" beach hunting, the MXT does quite well in wet, freshwater beach hunting, but I have had some challenges when working wet saltwater beaches. I found that I had my best performance with an MXT on saltwater beaches (wet) when I used a Double-D coil. My preference has been a 5" EXcelerator coil if I am hunting in a trashier site, but a 14" EXcelerator coil for coverage. I did use a White's 6x9 Eclipse and it seemed to handle the wetted salty sand better than the stock 950, but lacked the depth of the 950.
For what it is worth, give the MXT and accessory coils some serious consideration for the tasks you have.
<EM><STRONG>Monte
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