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Old 08-26-2012
Sunnyside_Oriental Sunnyside_Oriental is offline
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Re: Still holding its own - HF Radio

Quote:
Originally Posted by btrayfors View Post
Excellent article by Jeff, and a good summary of the value of SSB and of installation basics.

I install SSB's professionally, and I have just two things to add.

1. Fusing/circuit breakers. Jeff's right that good clean power to the radio is essential, and the example he gives is right on: AWG6 marine cable for runs up to 20' round trip, AWG4 for longer runs. However, you need a fuse or circuit breaker in BOTH the positive and the negative wires, located close to the house batteries. And, most circuit breakers will not meet ABYC specs insofar as ampere interrupt capacity (AIC) is concerned. AIC must be in excess of 5,000 amps, and only the new high-AIC Blue Sea Systems breakers will meet this standard. Much easier to use fuses. Two common types are OK for this purpose: ANLs and MRBFs. The smallest ANL you can find is 40A. MRBF's come in 30A sizes and up.

2. RF Grounding. This is a little understood part of SSB installations. The implication in Jeff's article is that wire can't be used because RF travels on the outside of conductors, so only use wide copper, etc. This is WRONG, despite how often you see it repeated in manufacturer's instruction manuals and in texts on SSB. If that were true, how would a wire dipole work? And how come it's the STANDARD against which all antennas are measured?

The use of aluminum toerails, lifelines/pushpit/pulpit structures, metal rubrails (like on Island Packets), and other solutions can work fine, but sometimes are a lot of work to implement. Radials, both tuned and untuned, work very well. There's no need to physically couple to the seawater. In fact, the evidence is that elevated radials work better than buried radials. One of the simplest effective solutions is to use the KISS-SSB Radial Counterpoise System....very easy to install, and it works as advertised.

Again, thanks to Jeff for his excellent summary of the use and value of SSB to the cruising community.

Bill
WA6CCA

Bill, I fully agree with most of what you have said except for your miss-understanding of skin effect. This is truly an effect of wire. I remember way back when I first started learning electronics in 1965.

The short version was when you run DC, the current flows across the entire diameter of the wire. As you increase the frequency it moves to the skin which actually represents a slight increase in impedance for the same level of voltage. Then the kind of funny part was when it get s high enough it leaves the wire and hence wive guide was developed. Wave guide is you have not used it is really coax without the center conductor.

In saying that at HF frequency, some of the signal clearly goes down the wire, but to your point a wire dipole makes a great radiator/dipole antenna.

Twin lead is an interesting concept that works well, but that does not mean that there is no skin effect.

I found a boat where a "Professional Installer" had installed GTO 15 between the Transceiver and the AT140 tuner. It had a very poor radiation as a result of the maximum possible reflected wave. So wire in RF is more than just wire, skin effect, etc. It also requires impedance matching to work in many cases. The Kiss ground is great, but it is really the other half of your 1/2 wave antenna using custom cut radials. e.g. a 1/2 wave dipole with the modifications made by the tuner to match the kiss and the back stay.

Terry AD7XL
Made Simple for Cruisers
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