This is the second CF unit from Holux that uses the IIe/LP chipset. This unit incorporates SiRF's new High Sensitivity technology.
According the the paper "Enhanced Sensitivity for Acquisition in Weak Signal Environments through the Use of Extended Dwell Times", which is published in the technical section of the SiRF website (registration required), the increased sensitivity is obtained by extending the signal integration times and lowering the detection threshold. The paper indicates that the performance of the ES software in weak signal environments is roughly equivalent to the standard software in regular and strong signal environments. There is no indication in either of the papers on their site that any form of position averaging is being used. (ed - they have confirmed that the delay is a "by-product" of the new software)
The unit is physically exactly the same as the GM-270, except it has the words "GPS Ultra" printed in white on the front of the antenna housing. It carries the part number 96016-01, while the regular Hoxux carries the number 96016-00. The Holux website carries no mention of this unit. The unit also has a jack for an external antenna, just like the original Holux.
The paper mentioned above indicates that one of the drawback to the changed software would be increased acquisition times. To test this the Ultra was compared with a normal Holux unit using GPSViewer. Each unit was set to "Cold Start" and time was measured to the acquisition of a 3d fix. As TTFF can vary even if done one right after another on the same unit, 5 TTFFs were done for each unit and averaged.
TTFF 3D: Ultra averaged a pretty consistent 1 minute longer to get a fix than the GM-270 Satellites locked: Ultra averaged a pretty consistent 2 extra satellites when it locked.
I have used the Ultra in a number of low signal environments that would have required the external antenna on my regular Holux. In every case the Ultra performed just fine inside the car. The Ultra will also receive a signal inside part of my house, where the regular unit will not.
A number of users have reported a "lag" in the position (ed - and especially speed) display when using the Ultra. The reviewer has seen this also with Routis and Mapopolis, however I do not find it disturbing. This is highly subjective, of course. In addition, PocketMap Navigator, at the 1000 level, shows no lag at all. (ed - PocketMap Navigator, has been fine-tuned to work with the Ultra, although the lag will still be present unless the speed is reduced).
As both units have the same hardware, it is expected that will be no differences in this category and none have been observed with my Ipaq 3955 and Nexipak dual CF unit.
Pros: - Incredible sensitivity pulls in a lock in the worst situation
Cons: - exhibits a "lag" (some software is being adapted to work around it) - longer TTFF
Rating: A and an A+ for specialized applications requiring high sensitivity.