Low signal strength

I have a Linksys WRT54GS with a DLink 7dbi high gain antenna, using WirelessMon I am trying to find deadspots in my network but even if I'm in the same room as my router/antenna my signal strength is -47dBm/53% at worst and -39dBm/62% at best, this just doesn't seem right to me, shouldn't my signal strength be 100% when the laptop is 6 feet from the router?

Does it actually record dBm or is it just dB?

I find it odd that 47dB?+53%= 100 and 39dB?+62% is approx 100. This would imply that the max level at 100%= 0dB?

Given that the WRT54GS using 11G is supposed to have a power output of approx 13dBm and you have changed the antenna for a 7dBi one then you would expect the output to be well above the capability of the utility.

Is there anything in the instructions that give you an idea of what the 100% signal is referenced to?
If it is based on RSSI measurements then it could depend on the manufacturer of the wireless card and how they implement it.

I wouldn't put great store in actual figures but concentrate on the levels relative to a reference point(say 1 Yard N,S,E or W of the AP) at each point of measurement. You are after all not using an expensive, regularly calibrated piece of test equipment.

Does it actually record dBm or is it just dB?

-I'm using netstumbler and it records dBm.

I find it odd that 47dB?+53%= 100 and 39dB?+62% is approx 100. This would imply that the max level at 100%= 0dB?

-From what I've read the max level of 100%=0dBm, I think it means there is no power loss from the router to the laptop.

Given that the WRT54GS using 11G is supposed to have a power output of approx 13dBm and you have changed the antenna for a 7dBi one then you would expect the output to be well above the capability of the utility.

-In the datasheet I've got it says transmit power is 15dBm, I'm not real clear on how dBi relates to dBm

Is there anything in the instructions that give you an idea of what the 100% signal is referenced to?
If it is based on RSSI measurements then it could depend on the manufacturer of the wireless card and how they implement it.

-I couldn't really find much help on the netstumbler help docs, sorry

I wouldn't put great store in actual figures but concentrate on the levels relative to a reference point(say 1 Yard N,S,E or W of the AP) at each point of measurement. You are after all not using an expensive, regularly calibrated piece of test equipment.

-I've already tried all over the house and the best signal I can achieve 39dBm

You will never get 100% signal at your laptop because you have to take into account "Free Space Loss"
Calculator:- Support :: Calculations :: Free Space Loss :: Terabeam Wireless

Input your Frequency 2400MHz
Distance between Antennas 0.001 Miles= 1.76 yards
Gives a path loss of 44.2 dB

If I assume the WRT54GS had a 2dB antenna before you changed it for a 7dB one and that the 802.11g output of the router was 13dBm
The output at the router should then be 13-2+7= 18dBm

The max signal arriving at your wireless laptop antenna will be 18-44.2=-26.2dBm
Your wireless card is not an accurate device at converting to power measurement and is probably dependent on how it's manufacturer does it's RSSI conversions. I get different results using different cards from the same location and different results using different scanners. You will also find that just turning the laptop around will give you a different result.
At this moment in time I get a reading of -36dB for my AP at 2 yards.