@chadwick90 The problem with the F-Fund is interest rates. Interest rates and bond prices are inversely related. As interest rates fall bond prices rise, and vice-versa. The Fed has backed itself into a corner. It can't cut rates any further without going negative.
Negative interest rates would trigger inflation as people are less likely to maintain funds in a bank. More capital in circulation, less productive use. Sounds weird but banks are a key part of the financial engine. Less productive use means more dollars chasing fewer products. So, the Fed is facing a double-whammy that has it stagnant.
At some point, interest rates must begin rising. Bonds values are guaranteed to fall. Thus, the F-Fund is going to take a major hit. This is why the F-Fund has trailed G over recent periods.
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Somebody want to step up and explain the downvote?
I suppose you could claim potentially increased coupon payments will offset some of the capital losses, but that requires sale of the current bond and repurchase. This will increase fund expenses. And being forced to pay higher coupons means many bonds will execute their call options. So that means many of these new bonds won't be delivering the YTM.