I hope I can help with your problem.
I agree that the discone antenna is a compromise, it is unity gain at best, meaning 0 gain. It does offer wide band reception, but not as good as a band specific antenna. It's great for wide band searching if you have access to a band specific antenna for real world monitoring.
Your friend had success with a two meter 144-148 MHZ radio because of the line loss related to the rg-8 cable. The higher the frequency the more the loss. Check out this site
http://www.timesmicrowave.com/cgi-bin/calculate.pl it shows the loss associated with the different coax cables by type and length of the run.
Keep in mind the more adapters you use, the more the loss. Google this concept and you will find a lot of information.
Just a quick side note the "radio ripoff site" is wrong as far as frequencies go ( as well as many talk groups) Intercept is much closer to reality. I see so many people on this forum link to un-verified information on frequencies, especially "radio ripoff". Please don't post information unless you have verified it personally.
Bottom line is the Comtelco antenna you purchased will more than likely outperform your discone, but the coax will limit the improvement. I suggest LMR-400. Try the calculator and you will see the difference. You need to put an N connector at the antenna and then do what it takes at the radio.
Bottom line is I can see the RS rubber duck doing better than the unity gain discone with high loss rg-8 coax which is designed for HF use.
Hope this helps.
Vince.