Former marine electronics director Andy Haines answers a reader's question about installing an SSB radio antenna. Got a question? Email email@example.com
Q: I recently bought a NASA Target HF3 SSB radio antenna receiver. The manual that came with it is OK but the instructions for the antenna includes a diagram of a house and a wire tied to a nearby tree – not helpful for marine instruments! There is also a diagram of a boat which refers to using an insulated backstay and connecting it to the receiver with a 70 ohm coaxial cable. But I’m not entirely certain an insulated backstay is necessary, and anyway mine divides in two about 3m up from the deck.
The mizzen mast has back angled shrouds as backstays. There is a simple 10m insulated wire antenna with phono plug supplied. Given the unhelpful instructions I’m not confident of following any of the advice. It says 10m is a ‘good compromise’ and says it should be as high as possible and away form mains lines and televisions. There is also a shorter black wire for grounding (‘to a cold water pipe or mains earth’!).
My intended use is offshore reception for news, weatherfax, navtex, radiotelex etc. My boat is an Elizabethan 31 ketch with a GRP hull.
- Is 10m of antenna a good compromise for offshore long range use?
- Do I really need an insulated backstay?
- Can I run the supplied cable up one of the mizzen shrouds (further than main backstays from the cockpit/source of interference?
- I read guard rails can be used as an antenna – but they are horizontal and low, so seem unsuitable to me…
- Please can you say what I may use as a ground?
Andy Haines replies: “I’d agree the manual could be construed as misleading, but a huge number of people buy receivers for home use, so it’s a question of trying to interpret what is in the manual and apply it to a boat. Sailing boats are fortunate in that they have masts and rigging sticking up into the sky.
“Motorboats do not, of course, so the best way forward in that situation is to buy Nasa’s SSB Active Receive antenna. You could also do that with a yacht and install the active antenna on the pushpit. However, a ‘long wire’ is about as good as it gets for SSB (Single Side Band) and all other AM (Amplitude Modulated) MF (Medium Frequency) and HF (High Frequency) reception, a good deal of this is DSB (Double Side Band) like BBC Radio 4 on 198kHz.
“So, to answer your questions one at a time:
- 10m is a good length for an SSB radio antenna reciever.
- The short answer is no, you do not necessarily need an insulated backstay if you’re receiving signal only and not creating high radiated RF (Radio Frequency) power or energy from a transmitter. So taping or cable tying the 10m wire up the back stay (or other stay) would be an OK compromise and from my experience is perfectly good enough for a receiver. There will be some loss of performance (compared to an insulated stay) because the wire is secured adjacent to the stay over its entire length and this will have a derogatory effect to a degree.
- Yes, you can use any stay. The mizzen shroud is further away from most sources of interference, but the route through the boat will be longer and this could result in more interference, so it’s a real six of one and half a dozen of the other conundrum. It’s better to keep the cable run inside the boat as short as possible and get the wire out into the open where it will do most good.
- You could use the guard rail as the antenna, but generally speaking a back stay is the best, primarily because you can achieve height. Height is not necessarily key to HF reception but it will help because it gets the antenna away from interference and the signal to noise ratio is likely to be better. That means you’ll receive more signal and less interference (in theory).
- The ‘Ground’ or ‘Earth’ ideally needs to be a ‘sea earth’, in other words metal that is connected to the sea.
“A seacock can be a good solution and you can secure the earth wire to the seacock with a Jubilee clip. If the vessel is DC negative earth (which it almost certainly is), you could connect the earth to the engine, which of course in turn is connected to the sea.
“Always try to keep earth cables as short as possible: a long earth wire acts like an aerial and picks up the interference you’re trying to get rid of! Try to site the SSB radio antenna receiver as far away as reasonably possible from sources of interference (engine alternator, fridge, battery charger etc). But this a boat, everything is close, so you have to make the best compromise with every decision. Also make sure the 12V power feed is as ‘clean’ as possible by taking it directly back to the distribution panel.”
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