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Old 22-08-2008, 05:34   #1
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VHF & HF SWR meter and installation

I have a yacht in Malaysia and I have to remove the mast for painting and Repairs,
Currently I have a whip aerial for the HF Radio and a AT 120 Tuner below the deck very near it.
I am considering installing a HF aerial on the top of the mast however it has a VHF aerial installed.
Questions 1
I noticed the HF aerial has a damaged tip should I cut this off and seal it. I Know the VHF radio Lengths need tuning is this the case with HF Aerials
If I need to how do you do it.
There is no radio people to call to fix it where I am
I am going back over there soom and I can take a SWR Meter with me
2.
Can the HF & VHF Aerial be the same aerial with out a lot of issues
can I put the 2 close as on top of the mast.
3
Should I leave the HF Aerial where it is as the Tuner would need to be moved and that is a big job to hide it near the mast
4
Can I use the VHF Aerial and the 27MHZ Aerial as one or should it be seperate
5
should I have a SWR meter on the output of the HF Radio
I have a Icom 78
I am an electrician however not had much to do with VHF HF Radios
Any help would be appreciated
Regards
Rossmonty
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Old 22-08-2008, 06:23   #2
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To borrow a phrase from another profession, "If you want three opinions on an antenna, ask two radio techs".

Having said that, here is my two cents worth.

1. Assuming it is ONLY the tip of the HF whip that is damaged, cut it off and seal with sealant of your choice. If it is a fibreglass former, then seal with fibreglass as first choice. The AT 120 tuner will take care of any slight change in electrical length of the whip antenna.

2. No, HF and VHF antennas can't be the same antenna. There is no real advantage in putting the HF antenna (assuming its a whip, not a long wire) on top of the mast and there would be significant technical difficulities in doing so.

As the VHF radio waves are propagated by line of sight, there is considerable advantage in having the VHF on the top of the mast. However, the HF waves are propagated differently (ground waves and sky waves etc) and therefore the antenna does not need to be so high.

3. Yes, leave the HF antenna where it is assuming it has been working OK in that location. There are other possibilities like a long wire backstay antenna etc but if it works, don't fix it.

4. VHF and 27 MHz antennas have to be different.


5. VSWR meter is not really necessary on the HF rig but is a "nice to have" option and certainly will allow you to troubleshoot antenna problems and perhaps get better performace out of the system if you take the effort to learn all the ins and outs of the mystical (and some say "black") arts of antenna theory.
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Old 22-08-2008, 18:39   #3
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Hi Wotname, Thanks for that I asked the question with your answers in my mind but better to ask and find out something new than not ask at all.
I think I'll take a VSWR meter over for the hell of it.
I have a back up VHF Aerial system I want to install if ever I am demasted (*** forbid) and I need to run cables aft to the Aerial. I'm going to swat up on VHF & HF Systems in the mean time.
Any suggestion on Books or websites to checkout
Regards
Rossmonty
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Old 22-08-2008, 19:32   #4
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Maybe some others will chime in with suitable books /websites but I will try to suggest something in a day or so (nothing comes to mind this morning and I have a busy day ahead continuing the refit ).
Just check your VSWR meter is capable of the freq. in the HF and VHF band, most (but not all) are and is suitable for the power ranges. In your case 100 watts for your HF and 25 watts for VHF. I apologise if you know all this stuff already .
How is Buderium these days, still the jewel in the crown of the Sunshine Coast. I used to live in Burpengary for awhile in another life and sail out of Scarborough.
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Old 22-08-2008, 20:40   #5
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One suggestion for book - ARRL Handbook. This covers most things in the RF world and is, IMO, a good all round refernce book. It is not too esoteric and fairly readable however it is not a simple "2 page guide to basic antennas".
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Old 23-08-2008, 10:55   #6
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I agree almost 100% with wotname...good advice, IMO :-)

The "almost 100%" is because I'd move the SWR meter from the "nice to have" column to the "really should have" column....in any HF installation.

Get a good one. Best one on market now is the CN-101L Daiwa...about $99 on-line price. Well worth it. Has a light, too. Cross needles (power and swr); good build quality, like all Daiwa stuff.

One thing not mentioned above is the RF ground system. This is critical with a whip antenna or any sort of end-fed antenna (e.g., backstay). Be sure that all connections are very clean and very tight. Simplest RG ground is a length of wide copper (2-3" or more) led from the tuner to the nearest bronze thru-hull. More elaborate schemes can add a bit to the setup, or even a substantial amount if you go all-out.

Depending on what bands you intend using, an "alternate backstay" antenna consisting of at least a 40' length of s/s insulated lifeline works well and will outperform the vertical on the lower bands. Something to keep in mind for the future.

Good luck,

Bill
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Old 27-08-2008, 04:26   #7
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Thanks for the advice

I am going to Buy a VSWR and Keep it on the boat, Amazing that in Asia there is no techs available when you want them, as well for a lot of other things as well
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