The DAP105/DAP125 are Differentially Amplified Probes for use with the D-105 Test Set. Unlike conventional probes with a single point of pickup, the DAP incorporates a two sided paddle capable of amplifying signal differences between each side. This feature is especially useful when sensing TriPlex, the preferred tone when bleed-over or cross coupling appears on adjacent pairs.
The DAP105 and DAP125 both have the ability to sense low frequency tone such as 577, 987, and 1004 Hz.
The DAP125 expands the operating frequencies into the DSL region. The D105 Test Set provides two modes of operation, manual (SNOOP), or automatic decoding (CKT-ID). Each method has it's advantages and disadvantages.
The SNOOP mode sets the internal receiver to the desired frequency for signal decoding. The level of the signal is displayed on the LCD along with gain and volume selections, and the decoded output is routed to the speaker. The manual mode works best when scanning through a module, frame or cross-connect. The disadvantage is that the user must select the frequency (service) on which to listen.
In the automatic mode, CKT-ID, the D105 Test Set scans several key frequencies, makes it's decision as to the type of service based on an internal spectral template, and displays the results on the LCD. The speaker is used to alert the user of the bandwidth detected by outputting a higher pitch audio for greater bandwidth services. As an example, for HDSL the tone heard would be 800Hz, for VDSL the tone heard would be 1800 Hz. So when DSL is detected the user hears a clean clear tone. The disadvantage is that in some cases, due to overlapping frequencies, the CKT-ID method could identify the DSL type incorrectly, such as VDSL service at customer premises.
 The DAP105 or DAP125 for Tone Location |
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 The D105 with DAP125 identified a T1 circuit |  SD105 with DAP125 probe found a VDSL circuit |
D105 with DAP125 in SNOOP mode found HDSL