FM/LW radio aerial?

Seagreen

Seagreen

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I think that the Cd/FM/LW Car radio in the boat needs better reception to get FM and LW broadcasts, especially for LW shipping forecasts. (Don't have or want navtex).

I also have lower shrouds paired as a continuous loop up to the hounds and back again to the chain plates - its an old boat with a wooden mast.

It occurred to me that I could attach (solder maybe) some short connectors to the top Stainless steel bolt at each stay (or maybe just loosen the bolt and add copper wire loops, and attach the aerial to these. Better than a this plastic coated wire running round the shelves inside.

Or is this a recipe for A) lightning strikes or B) horrible electrolysis problems in a wooden boat fastened with a mix of Copper, silicon Bronze and old iron nails?

The VHF aerial is already attached to a splitter for the AIS. Can the panel suggest a good solution?

TIA.

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No I disagee the car aerial will not give much improvement over the bit of wire around the shelves.
For LW/MW you need a long wire. Your use of the shrouds may well be the best arrangement. If that is no improvement then try a long piece of plastic covered wire hoisted to the mast top on a halyard. This may be better.

Many radios have a little screw adjustment through a hole in the cover. called antenna trim. If you can find this then turn it for best results on the long wave or MW. The radio wopuld have been tuned to allow for the capacitance of typically 2 metres of cable to a car aerial. This is a type of coax but low capacitance. Even so the capacitance is significant to the tuning of the input circuits. The adjustment is to allow for different cable lengths. If you can't find an adjustment then you might find a few metres of car aerial cable between the radio and the antenna usefull.

good luck olewil
 
Don't know if this helps - I use a spare VHF aerial on the pushpit to feed the FM/AM radio and the AIS engine via a simple splitter.

This works well on the FM side, and also for MW. However, to receive LW I need to disconnect the earth side of the arial (by uncrewing the plug so that only the central pin makes contact).

Perhaps one answer might be to connect the aerial input by a simple wire to the guard rails ?

John
 
If you use an EasyAIS VHF splitter, you will find the dedicated broadcast radio receiver output provides very good reception over a very wide band of frequencies, not just at VHF. I often use it instead of the backstay antenna for weatherfax reception at HF and it still works at the very low Navtex frequencies too, so should be fine for LW.
 
Hi seagreen almost certainly the coax you have is RG58 50 ohm coax. The cable used for car radios especially for MW/LW reception is more correctly described as a screened cable. It has much lower capictance.

This is because a 1/4 wave dipole tuned antenna giving 50 ohm impedance will be many hundreds of feet long. So our little bit of rod at MW or LW presents a very high impedance. You might say the low impedance 50 ohm coax will waste away much of the signal.
Worse the antenna input in the radio is connected to a high impedance feed point on the first tuned circuit essentially in parallel with the tuning capacitor. Hence the cable capacitance (something like 20 pf per foot) will stuff up the tuning which may have a variable capacitor of about 50 to 400 pf. (picofarrad) Reducing the signal even more.

That is why at least older car radios had a trimmer capacitor to account for various screened cable lenghts. Possibly newer radios are set up for a typical antenna cable length.

This explains why one poster gets better reception using his VHF antenna with the earth screen disconnected at the radio. This makes the antenna and all the cable outer and inner the antenna with no ground.

Anyway after all that waffle don't try to use 50 ohm cable for the radio on LW/MW. Just use bare wire into the centre. olewill
 
Thanks for that. I think it means that my best bet is to use a standard car aerial concealed somewhere. This is do-able, but I just thought I'd get better reception with a longer and higher wire in the air, thus the shrouds. Also, any aerial would usually be hidden in the hull and mounted in the horizontal plane not vertically though I could perch it atop the mizzen next to the VHF, but could this also cause problems?
 
For a few years we have had very poor Long Wave radio reception with interference and generally no signal. LW is important to us as the BBC shipping forecast is broadcast 4 times a day but we like Classic FM too so we needed an aerial that would work with all frequencies.

Some have suggested about using a splitter from the VHF aerial but we have had poor performance on MW and LW frequencies on the VHF aerial so a different solution was required. We have found that connecting onto a stainless steel stanchion is the best reception by far.

Connect a long aerial lead to your radio and then touch the centre onto the rail. Go round all the rails on your boat. We tried the main gunwales SS stanchions but LW reception was poor. We tried using the GLOMEX but useless on LW and average on FM. We tried a SS post in the centre of the boat. We tried the GSM aerial which was good for FM. We tried the 2nd spare VHF aerial but just OK. We were going to be content with that but then as a last try we touched the flybridge SS railing. FM was perfect with good long range stations clear, MW good and LW great !! LW is very hard to get good on a radio.

http://poc.forumup.co.uk/viewtopic.php?t=9&mforum=poc

Hope this info helps
 
Hi Seagreen. I may have been a bit pedantic about input capacitances. Your best bet is bare wire into the antenna socket. Make it as long as possible and yes try it connected to rigging.
If you wan to try a car radio aerial yes use the cable and conjnect additional wire to the aerial or in place of the aerial.
One of the problems is that the requirements for LW/MW are just so different to VHF FM and the antenna is made hopefully as a compromise for both. good luck olewill
 
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