What are good settings to use for Tx Power and Antenna Gain with dd-wrt on my router (WNDR3700v1)? Currently, it is set to the defaults of 20dbm for Tx power and 0dbi for antenna gain. I want to push the envelope without getting the FCC to come knocking at my door. Has anyone done this before?
I have experimented with many routers using DD-WRT setting up long distance wireless links, and honestly I have not noticed much gain raising the TX from the stock output to the limit of 251mw. I notice no difference over 70mw on a WRT-54G, a WHR-G300N, a DIR-825, a DIR-615, an E3000, and several others. Some of them I haven't noticed any difference at all raising the TX any amount. All of the routers I have listed I have tested over a distance of two miles using 19dbi gain yagi antennas on each end.
Just experiment a little bit, raise your TX and see what your signal strength is at distance. You will likely come to the same conclusion I did, there is no need to pump excessive wattage through your radios (which is also hard on your power adapters... I have replaced several) if your not going to see any increase in signal strength.
A bigger antenna will give you much more signal strength at distance than increased wattage will, and it will do so without taxing your radios and power supply.
I will also add that excessive wattage through your antennas that are not big enough can also create signal distortion, which can actually decrease perceived signal strength. To use an analogy, imagine your antenna as a speaker and your router as your stereo receiver. If your speaker (antenna) is small your music (signal) will be distorted if your receiver (router) is set at full volume (TX).
The Antenna length must fit to its frequency, its Wave length.
Look here to find out your needed Frequency: https://en.wikipedia.org/wiki/List_of_WLAN_channels
For most used WLan its around 2445MHz. Now calculate the needed length: https://www.easycalculation.com/physics/electromagnetism/antenna-wavelength.php
The best Antenna you can have for that is full Wave length with: 4.92 Inches or 0.1249 Meters. Thats long, but you can cut it in half as much as needed and get half-, quarter- and smaller results.