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Old 24-12-2019, 17:40   #1
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SSB / Wx antenna sharing

I have a weather fax receiver/printer that needs an antenna. I tried using my VHF antenna but performance was really poor, I guess because it is designed for different frequencies. I also have an SSB that uses an antenna tuner hooked to the backstay for its antenna. Can the tuner/backstay setup somehow be shared with the weather fax?
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Old 24-12-2019, 18:13   #2
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Re: SSB / Wx antenna sharing

In order to do this, you would need an antenna switch, not an antenna splitter. The switch would need to be the best you can afford. Since the tuner has a pretty good bandwidth, you could tune the radio on a frequency near the WX frequency, then turn the radio off, switch from radio to fax, and start your reception.


One other possibility is to install another antenna dedicated to the fax. Caution must be taken to ensure your fax receiver is off before using the SSB. There is a possibility of front end overload.
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Old 24-12-2019, 18:23   #3
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Re: SSB / Wx antenna sharing

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In order to do this, you would need an antenna switch, not an antenna splitter. The switch would need to be the best you can afford. Since the tuner has a pretty good bandwidth, you could tune the radio on a frequency near the WX frequency, then turn the radio off, switch from radio to fax, and start your reception.


One other possibility is to install another antenna dedicated to the fax. Caution must be taken to ensure your fax receiver is off before using the SSB. There is a possibility of front end overload.

Yes! A switch sounds really good, I did not know the tuner could be used as you suggest. I'll give that a try. I really don't want to add yet another antenna for a device I don't use very often.
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Old 24-12-2019, 18:36   #4
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Re: SSB / Wx antenna sharing

Try it without tuning first. See if perhaps it can be used in the bypass mode. Also, I am not sure what the tuner does when the radio is turned off. It is possible that it defaults to bypass mode. Since you are only receiving you can leave the SSB on as long as you do not key the radio. Remember, the antenna switch will disconnect the radio from the antenna presenting a very bad "no load" condition to the radio.


Good luck.
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Old 24-12-2019, 20:25   #5
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Re: SSB / Wx antenna sharing

You want to eliminate the tuner from the WXFax as it will attenuate the receive signal if not tuned to the proper frequency. Most autotuners used on boats do not have a means of by-passing it.
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Old 24-12-2019, 22:27   #6
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Re: SSB / Wx antenna sharing

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Remember, the antenna switch will disconnect the radio from the antenna presenting a very bad "no load" condition to the radio.


Good luck.
This means your SSB will be very likely toast if you try to transmit without antenna connected.

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Old 25-12-2019, 09:03   #7
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Re: SSB / Wx antenna sharing

For wx you want a:

quadrifilar helix antenna
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Old 25-12-2019, 10:56   #8
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Re: SSB / Wx antenna sharing

and that brings up the interesting question - is weather fax information being received via HF or VHF? For HF, the same antenna can be used as for SSB operation. For VHF, WEFAX is in the 137MHz band which is satellite based. The recommended Quadfiliar (Quad) Helix antenna is used for ground stations; not sure how it will perform on a pitching boat.
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Old 25-12-2019, 12:26   #9
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Re: SSB / Wx antenna sharing

It seems to me that you are just looking for trouble by sharing the antenna, for little benefit. There are just too many ways that something can be damaged. Tuners are only needed for transmitting; a random length wire or whip will do a fine job of receiving HF. Don't overthink this.

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Old 25-12-2019, 13:31   #10
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Re: SSB / Wx antenna sharing

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It seems to me that you are just looking for trouble by sharing the antenna, for little benefit. There are just too many ways that something can be damaged. Tuners are only needed for transmitting; a random length wire or whip will do a fine job of receiving HF. Don't overthink this.

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If the tuner is tuned to say 8mhz, does that do anything to improve the 8mhz reception?
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Old 25-12-2019, 14:15   #11
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Re: SSB / Wx antenna sharing

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Greg
If the tuner is tuned to say 8mhz, does that do anything to improve the 8mhz reception?
Not as I understand it. However, if there is a tuner that is tuned to a different frequency it might reduce reception. The point of a tuner is to adjust the "virtual" length such that the power is directly radiated and not reflected back into the output transistors, where it would create heat instead of being radiated. That is what the SWR (standing wave ratio) is about. A low SWR means that the power is being radiated, while a high SWR means much of the output ends up back in the transistors, and potentially damaging them (which is why most rigs shut down output with high SWRs - to protect the hardware). A receiver doesn't have such concerns. Note that most portable short wave receivers come with a long wire antenna, or an adapter for one - that is all that is needed, along with a good ground (counterpoise).

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Old 25-12-2019, 16:31   #12
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Re: SSB / Wx antenna sharing

I was under the impression that the OP was using HF WEFAX and not VHF. If it is indeed VHF then my original comments are moot. One can easily place a sign on the front of the SSB saying "check the antenna switch before turning on SSB", or words to that effect.
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Old 26-12-2019, 01:42   #13
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Re: SSB / Wx antenna sharing

Murphy never sleeps........


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Old 26-12-2019, 03:26   #14
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Re: SSB / Wx antenna sharing

Please tune me in. WEFAX alias WX is usually transmitted at 137 Mhz which is clearly in the VHF range and the quadrifilar helix antenna is widely used on racers like the VOR and is usually mounted at stern.
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Old 26-12-2019, 10:06   #15
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Re: SSB / Wx antenna sharing

WEFAX is a generic term that can mean any means of transmission of hard copy weather information. It is like xerox, which really is a trade name but now means any method or copying hardcopy information.


From the NWS - "Radiofax, also known as HF FAX, radiofacsimile or weatherfax, is a means of broadcasting graphic weather maps and other graphic images via HF radio. HF radiofax is also known as WEFAX, although this term is generally used to refer to the reception of weather charts and imagery via satellite."
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