Well it's not a surprise that it doesn't work. The impedances are grossly mismatched. While it is generally acceptable to go from lower to higher impedance, this situation is extreme and just won't transfer enough audio power to modulate. Did you obtain and read the spec sheets for mic and radio?
RS Super Cardiod Mic, XLR balanced, 600 Ohms outputhttp://www.radioshack.com/product/index.jsp?productId=2997390#tabsetBasic
Ten Tec Omni VII, unbalanced, >10,000 Ohms input
, Page 38http://www.w4ish.net/Manuals/pdf/588_manual_release_2.pdf
You need to provide an impedance matching transformer, or an active device.
Heil Sound sells a transformer, XT-1
which you would need to mount in a box. http://www.heilsound.com/amateur/products/parts
DX Engineering order:http://www.dxengineering.com/parts/hls-xt-1?seid=dxese1&gclid=COmhgunG6r0CFUNqOgodCnAALw
Audio Technica makes an inline transformer from 250Ohm - 50,000 Ohm, which may or may not work. http://www.audio-technica.com/cms/electronics/f4b735b4cabc30ea/index.html
Radio Shack has an XLR to unbalanced adapter/txfmr but no specs.
Shure makes one 300 - 40k Ohm.http://www.musiciansfriend.com/accessories/shure-a95uf-impedance-matching-transformer
Heil Info on Balanced to Unbalanced mic connections:http://www.heilsound.com/amateur/tips/129-balanced-to-unbalanced-wiring