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Go Back   SailNet Community > On Board > Gear & Maintenance > Electronics
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  #1  
Old 04-10-2010
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Coax Balun with PL-259 to Icom AT130

Can anybody help me on this? I'm in the process of testing a ICOM M-710 and AT130 tuner prior to installing them on my sailboat. For the purpose I bought a slinky antenna which features a coax balun. The balun has a PL-259 connector while the Icom AT130 tuner features a single wire with an eye strap connector.

Somebody can suggest a simple and practical way of connecting the antenna/balunto the tuner?

Thanks for any tips you can share with me

Scud
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Old 04-10-2010
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Scud,

Toss the slinky w/balun. Not needed and an unnecessary complication.

Use a random length of wire. Anything over 23' is good.

Then, you MUST have some sort of RF ground. I don't know where you're doing the "testing", but if it's for a single band you could just attach a 1/4 wave length of insulated wire to the ground lug on the tuner. That would tune very well, but ONLY on that band.

A bunch of wires, either 1/4 wavelength or random length, would give you a few bands.

Bill
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Old 04-11-2010
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Thank you Bill. That is definitely my plan once I ll be on water (a lanyard antenna ad a bunch of radials) ... but I'm home now and I dunno' weather radials can be efficientnna on land.

What I did so far was to connnect the slinky antenna directly to the IC-M710 via a RG58 short cable with 2 soldered PL-259 at each end. I connected the ground of the IC-M710 to my balcony rails too.
I was able to pick up very weak signals and a few conversations in what seemed mandarine or a garden variety of it. I didn't dare to try transmitting.

Now I wanted to give a try to the AT-130 tuner and I got stuck in this dilemma. After sleeping on it here is what I came up with.
The slinky antenna is a dipole (balanced antenna). Surely you would need a balun if you want to connect i directly to the unit (IC M710) since the line is unbalanced. And so I didn't anything wrong by connecting the antenna to the unit. But now the AT130 is designed to work with unbalanced antennas (wire and so). What if I take a short piece of RG-8 and I solder a PL-259 on the antenna end while on the other end I run the core wire into the AT130 antenna slug and the mesh to the AT130 RF ground slug?

Thanks
Scud
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Old 04-11-2010
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Scud,

As I said before, forget the slinky dipole. Here's why:

1. You are on land. You CANNOT transmit anyway (unless you're a ham and are transmitting on a ham band). You cannot even use the "Tune" function to tune the antenna coupler....it causes the transmitter to emit a (reduced power) signal.

2. If all you're doing then is listening -- not transmitting -- any wire stuck into the M710 antenna connector will do.

3. Yes, radials work equally well on land. And they work very well if elevated. However, this is irrelevant in your case for land listening.

Couple of other things:

If you're bent on using the slinky, just plug it directly into the M710 and forget the tuner. As explained above, you can't transmit anyway on land.

The slinky dipole is a balanced antenna, but coax is unbalanced. That's why they put the balun there. Again, this is irrelevant for listening only.

Bill
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Old 04-11-2010
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I think we all know the FCC is not going to fine you for simply testing an antenna/tuner with a marine radio on land.

There are a couple of options -
short across the coax feedline of the antenna or remove it entirely from the dipole and short across both halves of the dipole; connect one end of the antenna to the tuner post and ground the ground post of the tuner to anyplace convenient. This isn't the best option but will allow you to determine if the tuner/transceiver are working.
Alternatively, any random length wire of min wavelength connected directly to the tuner will work.
You could also bypass the tuner and simply connect the dipole to the transceiver tuned to the antenna's resonant freq.
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If all you want to do is to test the tuner using the tune function of the M-710, then just hook them together without an antenna or ground at all. When using the tune function of the radio, the tuner causes the radio to transmit a 10 watt continuous signal. The tuner switches in an attenuator so that only a few milliwatts actually goes to the antenna terminal. You should hear the relays chattering a bit while the radio's "TUNE" indicator flashes and then the radio will show "TUNE" when the tuner is done. If it doesn't want to tune successfully, then throw a few feet of wire on the antenna terminal and on the ground stud. I'm a service tech and do this all the time to check Icom tuner's. DO NOT attempt to transmit full power with this setup as it can damage the tuner/radio. Only do it using the radio's tune function to verify the tuner's operation.

Eric
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Old 04-12-2010
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Thanx everybody.
I think I'll resort to a length of GTO-15 struck horizotally between two poles just for the test ad give up to the slinky. And I'll use the tune function as recommended by fairbank.

The plan is to be done with this test as soon as possible and move on installing everything on the boat before june. Then, I hope, I'll be able to work out the learning curve quickly enough to catch up with you on air this time.

Scud
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