may be? 
There are many variables to answer your question and the results are seldom yes or no.
The Diamond RH77CA gets good marks as an improvement for a wider band of frequencies than a 1/2 wave Antenex for the 800MHz range. The RH77CA for me works at the house because the 800 system are close to home and the other frequencies are further out which are where the strengths of the RH77CA are. There are other choices for antenna, but I am talking about the ones I have. Your frequencies of interest have a lot to do with which antenna might improve your reception.
The next step up in reception would be the attic followed by the roof. Keeping in mind to keep the losses in the cable to a minimum or the increase by position is lost to the cable.
The GRE receivers are known for sensitive front-ends can get into trouble with intermods and overloaded when the antenna/transmission-line improves which can be off-set using the attenuator.
I hope at this point you see that it can be a crap-shoot to an extent. There are a number of pervious posts related to your question and many hours of reading to review them. I think part of the fun of the hobby is experimenting to find what works better or not. The down side sometimes is the money spend with marginal improvement.
Mike
