Re: QLG1 retirement; new QLG2 module provides many improvements


Hans Summers
 

Hello Chris
 
Is there an patch antenna on the board that you could also use, or is the external antenna the only option?

The supplied external antenna is the only supplied option. You could, I suppose, connect your own onboard patch antenna with some modifications, but the PCB has not been designed with this in mind. You can buy patch antennas and they aren't expensive. 

Now the reasoning behind this: when designing QLG1, the patch antenna was specifically tuned to match the PCB. The patch antenna was also supplied by YIC, the same manufacturer who made the GPS RF module. I had to first build and test QLG1 prototypes, then send one prototype to YIC's testing facility, so that they could tune the patch antenna to precisely match the characteristics of the QLG1 PCB (with its large groundplane). If you look at a QLG1 patch antenna, you can see that there are usually two cuts in the metalized top surface of the patch (see attached photo in which I have circled these in red). These are what brings the antenna to the correct 1575MHz resonance precisely, when used with the particular QLG1 PCB. This precise tuning and the large QLG1 ground-plane are what gave it such a high sensitivity. 

If I had chosen to use a patch antenna as the antenna for the QLG2, then I would have had to accept one of two options:

1) Use an off-the-shelf patch antenna, which would not exactly match the specific QLG2 PCB design. The probable result of this would be that the resonance would not be correctly on 1575MHz exactly, and that would result in a lower sensitivity. 

2) I would have to locate a manufacturer of patch antennas (other than YIC, who got fired) and send them a prototype to tune the patch antenna, then get the custom-made antennas tuned and produced - which would be both expensive and above all, time-consuming. 

Neither of these two options were attractive; it would be abominable to consider a QLG2 with lower performance than the QLG1; and since I was caught by surprise by the YIC antics regarding supply of another batch of the RF modules and patches, I did not have TIME to go through this custom patch tuning/manufacturing process. The QLG1 has been a vital part of the QRP Labs kit lineup and I do not want to endure a period of months without a GPS kit to offer, that compliments and is guaranteed to work easily and seamlessly with the other QRP Labs kits. 

The solution was therefore to use an active antenna, where the considerations of tuning the patch to the PCB, is already taken care of and worried about by the active antenna manufacturer, and doesn't need to be my problem. The active antenna contains the patch and a low noise amplifier which overcomes coax cable losses with a bit of extra sensitivity margin on top. While the patch may suit some people and the active antenna others, I think overall the active antenna is a pretty reasonable solution since it means you can site the GPS antenna perhaps higher up or nearer a window etc and get even better reception; furthermore it means the QLG2 unit can be installed with the kit inside a metal enclosure. Which is also why I made it an 80 x 37mm PCB, so it would be compatible with being bolted easily into an Ultimate3S kit enclosure. 

73 Hans G0UPL

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