Since you says that you have never seen the blinking green light even when outside, there is certainly an issue with the GPS. Are you using a USB 3 device in one of the USB 3 ports on the Pi? This is know to create enough RFI to jam the GPS If you aren't using USB 3 and still can't get a lock while outside, it's possible that you have a defective GPS unit.
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73, de KM4ACK
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km4ack