Using An External Antenna with the HTC Touch

One of the best features of the HTC Touch is the ability to connect an external antenna to boost the CDMA cell signal, for both voice and data. As I travel, I sometimes find locations where there is only marginal reception, or no reception at all. Why is it this always seems to happen in the best places?

I bought an external dipole antenna (13 db gain) on Ebay that is designed for CDMA (picture, right), with a patch cord that adapts it for use on the tiny RF input connector on the back of the unit. If you're looking for it, it's under the self-portrait mirror, just beside the camera lens. If you remove the back cover, you can pop the mirror out of the back casing to allow access to the antenna input. The mirror is attached to a short plastic tether that keeps it captive so you don't lose it, and you can pop the mirror back in when you don't need the antenna.

When measuring signal strength and trying to optimize antenna location, the usual bar indicator is not very useful as it can only show large changes in signal strength. All phones have a technician's 'field test' mode that shows a variable signal strength on the decibel scale. The code for the Touch is ##33284#. If you punch this into the phone keyboard, as soon as you enter the last # character it will recognize the code and enter test mode (no need to hit the 'send' key because it isn't a phone call).

There are 3 different screens: one for voice and 1X data (the old, slow data system that is still used on some towers), one for EVDO, and one for GPS. You can also adjust the refresh rate from the default of 3 seconds to a faster rate of 1 second.

Here's what the field test mode screen for EVDO looks like (it's called HDR for High Data Rate, which is the old name for EVDO):

This is what I receive in my office without an external antenna. The two parameters of interest are Rx Signal Strength and Rx Power, you can use either one to measure relative signal strength (I've used Rx Power here).

If I plug in the dipole antenna, I see that Rx Power level jump to about -65 dbm, reflecting a 12 db gain over the no antenna reading. Note that the decibel scale goes from negative through to positive, with zero considered a perfect signal strength, so -65 dbm is a stronger signal strength than -77 dbm.

Although 0 dbm is a theoretically perfect signal, the -77 dbm signal works very well and is entirely capable of delivering 1 Mbps or greater download speed. I've had it work well as low as -95 dbm, and only after it drops below -100 dbm does it start to fail.

The dipole antenna is omni-directional and therefore a good choice for my sailboat, as it won't fade in and out as I swing on the anchor. I also have a direction beam antenna (yagi) that I used previously for my old 900 MHz analog phone, but I found it didn't work much better than the dipole for my new phone, so I stuck with that.

The dipole antenna has a magnetic base that is designed to allow you to quickly pop it on the top of your vehicle, but it works just as well by itself. It is also optimized for both the 900 MHz band and the 1800 MHz band, which is why it probably works just as well as my old yagi (900 MHz only).

I found that it makes all the difference, making normally unusable dead signal locations into functioning locations, and normally weak locations into very good locations. This is important as the data speed varies greatly as a function of signal strength.

I probably won't take it any further than my dipole antenna as that seems to work fine for me, but if you have more extreme requirements with a remote location in a very weak signal area, there are exotic high gain antennas and active signal amplifiers (boosters) that can be purchased.

It is also important to note that EVDO is a totally separate signal from voice. It may use the same towers, but the antennas and transmitters are completely separate.

I often found I had perfectly useable data in locations where voice did not work at all, and I'm wondering if the power levels are higher since proximity to human heads is not such an important issue when using data, as the phone is usually nowhere near your head when surfing the net.

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