Challenger has foreshadowed rises in its wholesale rates to mortgage manager clients.In meetings with mortgage managers this week Steve Weston, head of wholesale distribution at Challenger, has foreshadowed increases of between 10 and 20 basis points in delivery rates on top of the 25 basis points' rise in the cash rate this week.Some Challenger customers appear to expect rises of only 10 basis points though others say the increase in the margin will be twice this.Like a lot of wholesale funders, Challenger's ability to keep funding mortgages is dependent on the availability and price of warehouses from commercial banks and their ability to refinance those loans in the secondary mortgage market.Market talk is that Challenger last week took soundings on pricing a mortgage-backed security (some say for $600 million, some say for half that) and that early price talk was in the order of 85 basis points over the bank bill rate for a senior tranche of prime loans.Plenty of other wholesale funders are making similar new year inquiries and receiving similar feedback from investors.Challenger added loadings of 15 basis points on fully documented, prime home loans back in September 2007, and added loadings as wide as 75 basis points on some no doc loans at the time. Other increases in variable home loan rates announced by banks yesterday are mostly of 25 basis points though AMP Banking, which has a tiny portfolio, lifted rates by 33 basis points to 9.02 per cent.