Originally Posted by SV Demeter
Ok so for example frequency is 8.140MHz so thats 8,140,000Hz? So wavelength is 36.85? Or do I have my decimals screwed up? Also the site referenced give the following options for wavelength:
So if I'm trying to calculate the optimal antenna length for tuning to 8.140MHz what parameters should I enter in the calculator?
Yes, you correctly calculated the free-space wavelength of 8.140 MHz. There's a catch though: physical antennas shouldn't be cut to the free-space length (or in this case, 1/4 of that length), due to us not living in a vacuum, and the fact that wires have finite thickness. Here's an equation that should get you close for a quarter-wave vertical:
Length in meters = 72 / (freq in MHz). With this equation, an 8.14 MHz whip should be 8.845 meters.
If you just cut a wire to this length and plug
it into your radio, I doubt if you will notice any difference. Here's how it might possibly
Run a length of 50 Ohm (or 75 Ohm, it doesn't matter much) coax from your radio to somewhere far away from your on-board electronics
, and close to a grounding point (chainplate, toerail, wire lifeline, a piece of bare wire tossed into the ocean, etc.) Connect the vertical to the end of the coax (center conductor), and your ground to the coax shield. This is your new tuned antenna, and it might at least reduce the pickup from your on-board noise sources. At the SSB
frequencies we're discussing, the coax loss isn't going to be a big issue, so you can use something small and cheap
If you're interested, a perfect 1/4W vertical does not show your coax a 50 Ohm impedance -- it should be much lower. In practice, ground loss and other factors raise the impedance, so the coax won't be horribly mismatched. You wouldn't want to use this setup for a transmitter, at least not without some fine-tuning and matching, but for the receiver it's OK.
Your receiver's antenna jack probably isn't 50 Ohm anyway. It might respond better to a half-wave vertical. As long as you are hearing atmospheric noise (that extra hiss when you attach the antenna), your antenna is probably good enough.
More geek info: The "active antenna tuners" mentioned here can help your radio if it is being overloaded by strong out-of-band signals. The tuner acts as a filter (as well as an amplifier). Some inexpensive receivers are prone to overload. I've used the Kaito receiver and have not noticed overload problems, but I'm in a pretty quiet area.