You do not state where you actually live, as this could make a difference as to the advice offered.
In general the UK consumer laws are similar, so I would suggest that the Supply of Goods and Services Act 1982 [as amended] may apply. click here
Doe's the packaging that the item was packed in, suggest that it will work and tune into the Sky channels that you use.Doe's the manufacturer state that they have a product suitable as a replacement to the item you purchased. Was the salesman given exact details of your requirements.
You also mention the 7 day return procedure, and certain points need to be taken into consideration. The item was purchased as a direct sale, so the Consumer Protection [Distance Selling] Regulations 2000 would not apply, and it would appear that the shop was offering the 7 day returns as part of their trading terms. You being on holiday for 7 days or more and not being able to try out the item, as no bearing on this fact, unless the company have printed and published terms which state differently.
Here is another link that may help click here