```Dear LF Group, ```Thanks to those to commented on the antenna loss measurements. I added the data from ZL2CA, and also some provided by G3NYK to the graph of results from my own antenna (see attachment). The empirical formulas for the loss resistance of the 3 antennas work out to: G3NYK (6m high, 30m long inv. L): Rloss = 4733/f^0.86 (for points below 600kHz only) ```M0BMU(8m high, 40m long inv. L): Rloss = 1550/f^0.75 ZL2CA(Don't know, but must be quite big!): Rloss = 142/f^0.50 ```So as the antennas get bigger, the loss resistance gets lower and falls off more slowly with increasing frequency. This is reasonable compared with big commercial antennas, which have very low Rloss (a few ohms or less) which rises with increasing frequency. The fact that loss resistance decreases as the antenna gets higher is consistent with the majority of loss occuring in the ground under the antenna - for a given antenna voltage, as the antenna gets higher, the E field at ground level will get lower, reducing the dielectric loss in the ground. This also explains why the (much higher) commercial antennas are not as significantly affected by this type of loss. It also ties up with G3AQC's "footprint" idea - increasing the area covered by top loading will also reduce the field at ground level, and result in lower losses. It seems most people do not use a loading coil to resonate the antenna whilst measuring the loss resistance using bridge methods; the reasons I did were: - The loading coil filters out most of the signal from the broadcast stations near my QTH - otherwise, these can put a watt or two into the unfortunate bridge detector, even though the antenna is not resonant. -Having the antenna resonant means you are measuring just the resistance, rather than the resistance riding on a much larger capacitive reactance. This means that, for a given amount of resistance unbalance, the voltage at the bridge detector will be much higher, and so the SNR at the null will be better. -Likewise, the effect of imperfect balance in the bridge transformer is less important when the antenna is resonant and purely resistive. This is especially so for errors in the phase between the voltages across the two bridge transformer windings, which will effectively transform part of the reactance into resistance. ```Cheers, Jim Moritz 73 de M0BMU -------------- Enclosure number 1 ---------------- * This message contains the file 'rloss2.jpg', which has been * uuencoded. If you are using Pegasus Mail, then you can use * the browser's eXtract function to lift the original contents * out to a file, otherwise you will have to extract the message * and uudecode it manually. ```