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#11
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use standoffs between SSB coax and backstay??
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#12
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use standoffs between SSB coax and backstay??
I guess you must have forgotten about your numerous posts
a long time ago (1 year +) where you expoused the use of GTO-15 when feeding your entire rig. Must have been a senior moment. Doug, k3qt s/v Callista "Larry W4CSC" wrote in message ... On Thu, 06 Nov 2003 09:29:20 -0500, Glenn Ashmore wrote: It was probably GTO-15. I would hope that who ever went to the trouble of adding the standoffs would know the difference. GTO is hard to tell from RG59 from a distance. Neon sign suppliers even have it in decorator colors. What the hell is GTO-15, some West Marine $20/ft trick? This isn't a neon sign with 40KV of 60 Hz on it....IT'S RF! All the insulation in the world isn't going stop the RF from leaking out, like it's 'spozed ta. Lionheart's tuner is hooked to its backstay with a stainless strap in a gentle curve held on with a stainless hose clamp. Now that we got the damned steel cable holdin' the boom up replaced with something that DOESN'T suck off the HF signal into the mainmast, it works much better......well, at least until the sun exploded wiping out the ionosphere.... 73 DE W4CSC NNNN AR |
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#13
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use standoffs between SSB coax and backstay??
Doug,
Holding those of us on the senior circuit to what we said in the past is simply not fare. Regards, Ron (I think?) |
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#14
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use standoffs between SSB coax and backstay??
Wasn't me. I never heard of GTO-15 before.....??????
On Thu, 6 Nov 2003 23:24:08 -0500, "Doug Dotson" wrote: I guess you must have forgotten about your numerous posts a long time ago (1 year +) where you expoused the use of GTO-15 when feeding your entire rig. Must have been a senior moment. Doug, k3qt s/v Callista "Larry W4CSC" wrote in message ... On Thu, 06 Nov 2003 09:29:20 -0500, Glenn Ashmore wrote: It was probably GTO-15. I would hope that who ever went to the trouble of adding the standoffs would know the difference. GTO is hard to tell from RG59 from a distance. Neon sign suppliers even have it in decorator colors. What the hell is GTO-15, some West Marine $20/ft trick? This isn't a neon sign with 40KV of 60 Hz on it....IT'S RF! All the insulation in the world isn't going stop the RF from leaking out, like it's 'spozed ta. Lionheart's tuner is hooked to its backstay with a stainless strap in a gentle curve held on with a stainless hose clamp. Now that we got the damned steel cable holdin' the boom up replaced with something that DOESN'T suck off the HF signal into the mainmast, it works much better......well, at least until the sun exploded wiping out the ionosphere.... 73 DE W4CSC NNNN AR Larry W4CSC "Very funny, Scotty! Now, BEAM ME MY CLOTHES! KIRK OUT!" |
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#15
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use standoffs between SSB coax and backstay??
Larry W4CSC wrote:
Wasn't me. I never heard of GTO-15 before.....?????? On Thu, 6 Nov 2003 23:24:08 -0500, "Doug Dotson" wrote: I guess you must have forgotten about your numerous posts a long time ago (1 year +) where you expoused the use of GTO-15 when feeding your entire rig. Must have been a senior moment. Doug, k3qt s/v Callista "Larry W4CSC" wrote in message ... On Thu, 06 Nov 2003 09:29:20 -0500, Glenn Ashmore wrote: It was probably GTO-15. I would hope that who ever went to the trouble of adding the standoffs would know the difference. GTO is hard to tell from RG59 from a distance. Neon sign suppliers even have it in decorator colors. What the hell is GTO-15, some West Marine $20/ft trick? This isn't a neon sign with 40KV of 60 Hz on it....IT'S RF! All the insulation in the world isn't going stop the RF from leaking out, like it's 'spozed ta. Lionheart's tuner is hooked to its backstay with a stainless strap in a gentle curve held on with a stainless hose clamp. Now that we got the damned steel cable holdin' the boom up replaced with something that DOESN'T suck off the HF signal into the mainmast, it works much better......well, at least until the sun exploded wiping out the ionosphere.... 73 DE W4CSC NNNN AR Larry W4CSC "Very funny, Scotty! Now, BEAM ME MY CLOTHES! KIRK OUT!" You'll find a lot of GTO-15 at neon sign shops. It's heavy voltage cable. -- Email sent to is never read. |
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#16
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use standoffs between SSB coax and backstay??
"Larry W4CSC" wrote in message ... Wasn't me. I never heard of GTO-15 before.....?????? Must have been a pre-senior moment. ta. Lionheart's tuner is hooked to its backstay with a stainless strap in a gentle curve held on with a stainless hose clamp. I thought you were feeding your entire rig as an antenna? Now that we got the damned steel cable holdin' the boom ... We sailors call that a topping lift  73 DE W4CSC NNNN AR Larry W4CSC "Very funny, Scotty! Now, BEAM ME MY CLOTHES! KIRK OUT!" |
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#17
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use standoffs between SSB coax and backstay??
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#18
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use standoffs between SSB coax and backstay??
On Wed, 05 Nov 2003 23:32:57 GMT, "Gordon Wedman"
wrote: The other day I was wandering around one of our marinas trying to steal ideas from other boats and I came across an aluminum pilot-house sloop that may have come over from Europe. I noticed that the SSB coax was held away from the backstay turnbuckle and wire by ~1 inch plastic spacers. I've never seen this before and the previous owner didn't do it on my boat. I've been thinking of upgrading the ancient SSB system on my boat and was wondering if these standoffs were something recommended. Anyone know about these? Thanks Gord Any time the output antenna "hot" of an HF tuner is near anything metal, a capacitor is formed between the antenna wire and the metal objects. This capacitor is in parallel with the output of the transmitter and must be minimized. If it becomes a substantial capacitor (wire close to object), the output tuning capacitor in the tuner will run out of range (low as it goes) and the antenna won't tune properly, especially on the upper frequencies. So, we isolate the wire as far as practical from all metal objects, especially large, grounded metal objects. It is also very important that the antenna lead on the antenna side of the tuner be STABLE, and not flopping around, which causes this natural capacitance to anything to CHANGE during transmissions. If the wire is moving around near metal objects, the shunt capacitance constantly changes, ruining the tune of the tuner. So, this boat had a proper installation.....isolated on long insulators with many of them that would hold the wire stable as it traversed the sheet metal. The effects of shunt capacitance in any HF antenna situation with long wires is on the OTHER end of the antenna from the feed point.....at the insulator at the top of the backstay. This point in the antenna is the highest impedance (nearly infinity we hope) point of the system. The voltage at the upper insulator of a shorter-than-quarter-wave wire is always very high. Any capacitance to a metal object causes a lot of the signal to be shunted off to that object, and mostly lost, wasted. So, it is very important to make sure the upper insulator is NOT installed too near the masthead, but back down the backstay a ways and the upper end of the insulated backstay is never near metal objects, like boom lifting devices made of stainless cable, etc. The tuning of the backstay will go all crazy every time one of these metal cables moves near the upper end of the backstay. We Geoffrey acquired Lionheart, an Amel Sharki 41 ketch, the owner reported the insulated backstay antenna didn't work very well and he never found out why. After I took it over I noted how close the boom lift was to the backstay when the boom was on centerline, where it made my signal on HF just SUCK! So, we changed out the metal cable for insulated line. HF signals are now very acceptable no matter where the mainsail ends up. Getting the metal away from the antenna's upper end high impedance point solved the problem. |
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#19
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use standoffs between SSB coax and backstay??
It is practically impossible to match coax cable to an end-fed antenna for
various bands, without traps or impedance matching tricks at the end of the coax. The outer insulation and even the core insulation of coax is normally not high voltage proof, so don't rely on it, certainly not near an "earthed" wire. Special marine antenna cable can be bought but is expensive. I used multicore green earthing wire and spacers. These can be made of 5cm pieces of white conduit pipe (UV stabilised) with two holes on each side to fix a tag to the feeder wire and the backstay. Wrapping around both, fixes it well. Perhaps shrink tubing would even make it more "professional". The wire has been there for more than 5 years and the plastic has not deteriorated. The inside wires were getting black, so soldering on both ends is necessary. I am now going to replace it by special multicore UV stable HV cable, neatly tied to the backstay. It is still the question if spacers are electrically better than tying a cable close to the backstay. The coupling between the feeder and the rest of the backstay makes the antenna anyway into an a-symmetrical off-centre fed thingie that may radiate well on one frequency but miserable on another. The tuner will make the whole system resonant but that does not guarantee good radiation or prevent RFI. Sometimes a dummy load would perform the same way. With spacers, a 600 ohm feeder could be created (at least for some length) to keep stray radiation at lower levels but it must be symmetrically fed and commercial tuners don't do that. Probably the best is trying it out, as there is not much calculation that can be done. Thick marine antenna cable tied to the backstay makes the system at least wind and foolproof. And pray for no RFI into the GPS and mobile phone antennas. ---- Kris VK4CPG s/v Marin Hedon |
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#20
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use standoffs between SSB coax and backstay??
I doubt the boat in question was using coax. I just didn't know the
correct term to use for this type of wire and used "coax". Subsequent to all the original discussion I had a closer look at the wire used on my boat (installed in 1983) and I see that it is, in fact, GTO-15. Says so right on the insulation. Now I just need to buy a decent SSB to hook up to the backstay after selling the old Motorola 11 channel unit. "Woody" wrote in message tt.net... In article , says... I see this all the time on cruising boats not most, not many but a few. I always try to argue with the person that installed it on the pros and cons but never get anyone that can talk rf to me. best I had was an extra class ham that just said it works better because I can hear the difference. Distributed capacitance should be taken care of by the antenna tuner (all random length end fed vertical wire antennas on boats have tuners I think) So I guess the reason is to keep stray rf from coupling and reflecting back from the backstay. I would think that a ? wavelength distance from the backstay to the gto-15 should be good. But since you will be using it on many bands I would guess that at least 1/8 wavelength at the lowest frequency would be someplace to start from. Maybe about 10 meters separation between backstay and gto-15 may make a measurable difference. 2 inches of separation, less then 1 electrical degree ROTFLMAO at anyone who says it makes a difference. sded wrote in message . .. "Gordon Wedman" wrote: The other day I was wandering around one of our marinas trying to steal ideas from other boats and I came across an aluminum pilot-house sloop that may have come over from Europe. I noticed that the SSB coax was held away from the backstay turnbuckle and wire by ~1 inch plastic spacers. I've never seen this before and the previous owner didn't do it on my boat. I've been thinking of upgrading the ancient SSB system on my boat and was wondering if these standoffs were something recommended. Anyone know about these? Thanks Gord Standoffs are highly recommended to eliminate coupling/signal loss between the leadin and the backstay below the insulators. I made mine by running plastic wire ties through shrink wrap tubing-a loop around the backstay, through the tubing, a loop around the wire. About 2" long is good. Not coax at this point, but High Voltage wire, BTW. Easy to do, and does help performance. If you are talking coax, and it is properly impedance "matched" at both ends, proximity to objects (metal or not) will have no effect. There is (should be...) no RF on the outside of the shield. OTOH... Most comments reference a single feed wire to the stay. In that case isolating the wire from nearby objects is very important for proper function. Woody |
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