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Old 20-11-2008, 12:50   #1
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Shortwave receiver

Shortwave receiver
I have inherited an uninstalled new ham radio transceiver with my yacht. It is a Yaesu FT-857D. It also came with a large antennae tuner. The Yacht is Aluminium so care needs to be taken with the grounding of the antennae (I believe you use capacitors to transmit the hf, but not the DC to ground) and there is no insulated backstay.
I plan to replace the standing rigging later, fit an insulated backstay and get some professional advice about the grounding situation.
In the mean time I would like to use the transceiver as a receive only device with a temporary longwire antennae strung up the rigging.
I have tried connecting a longwire to the central pin of 50 ohm coax but I don’t seem able to receive much.
I realize that with this set up without an antennae tuner if I tried to transmit the poor SWR would damage the transceiver but shouldn’t it work reasonably as a receiver only?
Do I need a balum between the 50 Ohm coax and the longwire?
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Old 20-11-2008, 13:04   #2
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That longwire attached to the center conductor of the receiver 50 ohm antenna socket should be OK for reception only. Actually making an impedance match might improve things a bit, but probably not dramatically.

Do you have some kind of a ground? That can make a pretty big difference.
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Old 20-11-2008, 13:21   #3
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Thanks for the reply. No I was hoping to avoid grounding given the potential problems with a metal boat. Does the ground connect to the braid of the coax?
Thanks John
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Old 20-11-2008, 13:57   #4
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Your FT857D should have a labeled ground attachment point, which should be equivalent to the coax braided shield at the radio end.

One way to tell if your antenna is doing any good is to tune the radio to the high frequency band you are interested in, and turn up the AF and RF gain all the way without the antenna attached. You should hear some background hiss, this being the noise floor of the receiver. When you attach your antenna, if it is any good at all for reception, you should at a minimum hear an increase in noise from your speaker, even if it is only atmospherica noise. If there is no noise increase, then there is either something wrong with the radio, or your antenna is no antenna at all.
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Old 20-11-2008, 17:45   #5
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I think you may have the capacitor issue backwards--capacitors in the ground connection to avoid electrolysis--but thats for later.

You should be able to receive something with a long wire connected to the center pin of the antenna connection on the transciever, but it may help to temporarily connect the ground on the receiver to the aluminum hull.

What you hear depends on where you tune and what mode. You should be able to hear AM broadcast stations between 600 and 1800 khz, then between 5 and 6 mhz and 7-8 mhz. Also USB traffic on the ham band between 14.175 and 14.325 mhz
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