Good day, I am trying to find a suitable external antenna/cable combo to fit a Mobilemapper pro with the hopes of increasing accuracy. I understand that the PM2 antennas will work, but are there any other alternatives that are pole-mountable and perhaps cheaper/more obtainable?
Modified By land Severer on 5/17/2009 at 10:52 PM

As far as cheap goes you can get a $29.95 or so timing antenna on ebay that the receiver recognizes as an external antenna. I have a cute 3" saucer shape and a 3" snowcone. Internally there is about a 1" patch antenna that is not centered over the mounting point. Either accepts a TNC connector, but a proper pole mount more than doubles the cost. The antenna cable costs more than the first 2 items. I have not tested accuracy, just the fact that they work.

Getting an older used antenna may or may not work. The older antennas generally draw more power than the newer receivers have available. I have an older Ashtech antenna that one of my PM2s recornizes as an external antenna. The other 2 don't see it. I believe that one unit is on the high end of the ouput setting tolerance while the other 2 are on the low end.

An alternative with an older antenna is an external power source to the antenna. With a 12 volt lighter adaptor from a Map 330 I have run a PM2 on every antenna I have including Ashtech Geodetic Whoppers from Z-12s.

Yes there are cheaper alternatives, but you pays your money and takes your chances that it will work for you.

Paul in PA
Modified By Lawrence Paul Lopresti on 5/18/2009 at 6:49 AM

Thanks for the informative response, Please define 'TNC connector.'
I have just begun 'experimenting'/entering the interesting and exciting field of GPS. I have field completed my first static survey using a pair of Locus receivers. I havent even post processed the results as yet. (Still leafing through the manual) I have been relying on this message board for all sorts of useful info & tips.
I have aspirations of entering the GIS field as well. Based on the type of equipment that I am using, it is not hard to see that I am working with a very limited budget.
I have seen in earlier posts where users have post-processed their readings from the MMPro units. I am curious to find out what kind accuracies could result using such a unit with a pair of Locus receivers - is this even possible?
My question on the external antenna is merely to satisfy my curiosity as to how accurate a result could I obtain if I were to spend another $200 or less on an external antenna.

"I am curious to find out what kind accuracies could result using such a unit with a pair of Locus receivers - is this even possible?"

As for using a MMPro for Survey Grade accuracy:

Unofficially: Perhaps
Officially: No. A resounding NO.

Stumpwater R&D along with a certain Oklahuman figured it all out and managed to keep it all "in the vault" at Area 52 for quite a while. Since then there have been some "leaked" documents.

Do a "search" above for "Mobile Mapping 'bout Mississippi" for a thread on what I found to be the Mappers accuracy without an external antenna, post processed in Mobile Mapper Office to a distant CORS as per design.

But if you want to play "unofficially", fork over the cash for a good ProMark2 antenna.

Dange

Modified By Dave Huff on 5/18/2009 at 1:00 PM

A "TNC" connector means the size of the connector from the antenna cable to the antenna. Older antennas generally had a larger diameter "N" connector. The 3" diameter timing antennas have the same size connector as the PM2 and PM3 antennas, so the same cable is used. The even smaller wafer antennas have a smaller connector or are hard wired.

As to the post processing you would do that in the Mobile Mapping software. Your Locus download and process into Ashtech Solutions so you must somehow bring those files together somewhere. On that I have no experience.

There are several ways an external antenna gets you more precise data.

1/ An antenna on a pole has a clearer line of sight to the GPS satellites. With a handheld your body can block some of the signal.

2/ A survey grade antenna has a much more precise electronic/physical center. Most are tested by NGS and antenna parameters required for precision are posted for all.

3/ A survey grade antenna may have a ground plane to reduce multipath and/or electronic filters to do the same.

With a cheapie antenna you get only # 1 not the more important 2 & 3.

!

I use my MM Pro as a static unit often, and have since it's original purchase. Although the PM2 antenna works perfectly with it, I have an antenna that came with a sub-meter unit that works perfectly (after having tested and proved the L1 Phase Center).

Using the external antenna with the MM Pro, start logging as a "Reference Station", and just turn off the unit with the power button when you are finished. Then, using the MM Office Software, download the file from the reeiver into your Ashtech Solutions job folder. Using the "load file from disk" option in Ashtech Solutions, add the file from the MM Pro into the Solutions job, and edit the site information as required. The MM Pro has the same firmware (although "masked") as the PM2 units. I mix and match several units in my daily work routine. As a matter of fact, today I had a HiPer on the POST, two PM2's on project controls, and the MM Pro on a site monument. All were processed in Ashtech Solutions. The PM3 was actually on recon duty (with shape files loaded with site information) while the others were chugging along.

The MM Pro is a very, very versitle tool.

jd

This was the sort of repsonse I was hoping for. I still have a ton of questions, but would like to try your suggestions first. I have been eyeing a bunch of antenna on ebay but have no idea which (cable/combination) will fit the unit. Thanks again.