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How to make a Stationmaster for hf ?
Hi all, do you remember the old CD Stationmaster antenna? It was a end fed 1/2 wave. I would like to make one and I believe there are plans around to describe how its done, but so far I have not been able to locate them on the net. Does anyone know of a link to such a page, or even a magazine article etc. My work Library is quite good with regard to old ham magasines etc.
Any assistance is greatly appreciated. thanks for looking Mike VK3XL |
How to make a Stationmaster for hf ?
In article ,
VK3XL wrote: Hi all, do you remember the old CD Stationmaster antenna? It was a end fed 1/2 wave. I would like to make one and I believe there are plans around to describe how its done, but so far I have not been able to locate them on the net. Does anyone know of a link to such a page, or even a magazine article etc. My work Library is quite good with regard to old ham magasines etc. The Stationmaster I'm familiar with is an end-fed collinear for VHF... doesn't sound quite like what you're speaking of. End-fed halfwave antennas for HF seem fairly simple to make, but also seem to have a reputation for being a bit tricky to get working well. The usual approach to matching is to use a tuned tank circuit, feeding the tank either inductively or at a tap point partway up the coil. http://www.aa5tb.com/efha.html shows one approach... this one uses an inductive link to feed the tank. The page at http://www.smeter.net/feeding/tunehalf.php has a copy of an article by Reg Edwards G4FGQ (SK) which shows the "tapped coil" approach, and has a link to a copy of Reg's program to do the necessary calculations. -- Dave Platt AE6EO Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior I do _not_ wish to receive unsolicited commercial email, and I will boycott any company which has the gall to send me such ads! |
How to make a Stationmaster for hf ?
VK3XL wrote in
: Hi all, do you remember the old CD Stationmaster antenna? It was a end fed 1/2 wave. I would like to make one and I believe there are plans around to describe how its done, but so far I have not been able to locate them on the net. Does anyone know of a link to such a page, or even a magazine article etc. My work Library is quite good with regard to old ham magasines etc. Any assistance is greatly appreciated. thanks for looking Mike VK3XL Mike, You are more likely to get an answer by asking the question in an Australian context... but then a.r.a.m is a pretty uncivil place. Next you could try Google, and it would turn up an article on Ron Bertrand's RadioElectronicsSchool: http://www.radioelectronicschool.net...onmaster-3.pdf .. Is it a good antenna? Well it seems to depend on the feed line as the 'other half' of the vertical dipole, so you should be assured of high current on the outer of the coax. There may be other articles. I note that quite a few of our new six hour hams with their shack on their belt use their Stationmaster unmodified with an ATU at the transceiver... and it 'works real good, SWR is 1:1'. Still, that is the downside of looking at the world through a SWR meter. Owen |
How to make a Stationmaster for hf ?
On 28 ago, 03:55, VK3XL wrote:
Hi all, do you remember the old CD Stationmaster antenna? It was a end fed 1/2 wave. I would like to make one and I believe there are plans around to describe how its done, but so far I have not been able to locate them on the net. Does anyone know of a link to such a page, or even a magazine article etc. My work Library is quite good with regard to old ham magasines etc. Any assistance is greatly appreciated. thanks for looking Mike VK3XL -- VK3XL High Mike, The stationmaster is a HW end-fed antenna with LC matching section (L between center of coax and radiator, C is capacitance between radiator and radiator support construction). You can make such an antenna for other frequencies (I did it recently for VHF air band). The advantage of the HW over de 1/4W antenna is the feed point impedance. Depending on the length/diameter ratio of the radiator, the end-fed impedance varies between about 300 Ohm and 3 kOhms. When the radiator is horizontally, close over a reasonable conducting ground, end-fed impedance may rise up to 10 kOhms. This will result in High Voltage at the feed point as well. The ground current (or coax screen current when no ground construction is present), is about a factor sqrt(Zend-fed/40) lower with respect to a 1/4W antenna (can be a factor 8). As long as the impedance that is used as ground (or counterpoise) is far below the end-fed impedance, the antenna works well. Gain and radiation pattern will be same as for HW dipole. There are some things that can go wrong. Most people tune by changing the length of the antenna. That may result in the radiator to work off-resonance, reducing the end-fed impedance and increasing the feed current for the counterpoise. So in my opinion best thing is first tune the antenna (without matching network and low power) to minimum counterpoise current (measure with current probe) and then do the matching network. For the LC matching network, the C can be the capacitance between the radiator and the metallic structure that supports the antenna. I prefer the LC network above the LC tank circuit because of the higher Q-factor of the tank circuit. This reduces the useful bandwidth of the antenna significantly. As the matching is under the radiator, tuning is not that easy. When you need further information, don't hesitate to repost. Best regards, Wim PA3DJS www.tetech.nl |
How to make a Stationmaster for hf ?
Wimpie wrote in news:1188313351.276557.292100@
22g2000hsm.googlegroups.com: clipped... a nice description of an end fed vertical half wave with matching network. Wimpie, I think the OP had using the stationmaster radiator element unchanged on lower HF bands. You could view this as a 5.5m long radiator sitting on say, a 4m metallic support mast, fed at the junction of the two. Typically the configuration involves no radials at the base of the 5.5m radiator, and an shabby connection to earth at the base of the supporting mast. If at 80m you were to assume the earth resistance was as good as 30 ohms, the earth loss alone would account for 60% of the power reaching the feedpoint when the antenna is modelled without provision for current on the outer of the feedline. So, the StationMaster as described in the article is typically a ground mounted ~1/8wl vertical with an inadequate ground system, elevated feed, high sensitivity to noise, highly susceptible to RF in the shack unless the feedline is decoupled adequately. It is a little better on 40m, but all of the issues remain. A lot of the guys wanting to do such a thing are our new six hour hams, and they would be principally interested in 80 and 40m. Owen |
Thanks all for your replies. They have given me enough info to embark on the intended project. Again thanks for your help.
Mike VK3XL |
How to make a Stationmaster for hf ?
On 29 ago, 00:36, Owen Duffy wrote:
Wimpie wrote in news:1188313351.276557.292100@ 22g2000hsm.googlegroups.com: clipped... a nice description of an end fed vertical half wave with matching network. Wimpie, I think the OP had using the stationmaster radiator element unchanged on lower HF bands. You could view this as a 5.5m long radiator sitting on say, a 4m metallic support mast, fed at the junction of the two. Typically the configuration involves no radials at the base of the 5.5m radiator, and an shabby connection to earth at the base of the supporting mast. If at 80m you were to assume the earth resistance was as good as 30 ohms, the earth loss alone would account for 60% of the power reaching the feedpoint when the antenna is modelled without provision for current on the outer of the feedline. So, the StationMaster as described in the article is typically a ground mounted ~1/8wl vertical with an inadequate ground system, elevated feed, high sensitivity to noise, highly susceptible to RF in the shack unless the feedline is decoupled adequately. It is a little better on 40m, but all of the issues remain. A lot of the guys wanting to do such a thing are our new six hour hams, and they would be principally interested in 80 and 40m. Owen Hello Owen, I was expecting that he would scale the design to another frequency to assure half wave operation at the design frequency. If one is really planning to do what you described (using the 5.5m radiator from 80m..40m and upwards), it is a far from optimal choice for transmitting. At 80m, the radiation resistance is still less then 2 Ohms, at 40m about 7 Ohms, so assuming 30 Ohm ground resistance will result in a poor efficiency (about 6% at 80m and 19% at 40m). Off course when one makes a large ground network, efficiency will be better. Best regards, Wim PA3DJS www.tetech.nl |
Quote:
The info collected so far is at least a starting point for the conversion of this antenna. Thanks to all who have given input, it is greatly appreciated. Mike VK3XL |
How to make a Stationmaster for hf ?
VK3XL wrote: Hi all, do you remember the old CD Stationmaster antenna? It was a end fed 1/2 wave. I would like to make one and I believe there are plans around to describe how its done, but so far I have not been able to locate them on the net. Does anyone know of a link to such a page, or even a magazine article etc. My work Library is quite good with regard to old ham magasines etc. Any assistance is greatly appreciated. thanks for looking Mike VK3XL -- VK3XL I tried something similar in the past but had trouble with the capacitors arcing at 100 watts. Better reults were obtained using a stub made of ladder line. No coils No caps. Antenna was a temporary half wavelength vertical made of 1 inch electrical conduit working aginst a 6 wire groundplane. Base insulator was a beer bottle. Jimmie |
How to make a Stationmaster for hf ?
On 30 ago, 02:53, VK3XL wrote:
Wimpie;590418 Wrote: [removed] My intention is to use this antenna on the 10 meter FM section of the band. I have been given a 1/2 wave "Ringo" antenna that is missing the ring. I intend to convert it to the "stationmaster" type antenna as I think it will be easier to get the matching system right using a coil spaced from the bottom of the radiator than try to make a new matching ring etc. Thus if I could locate plans for the making of such an antenna it would save me a fair amount of time in the calculations and cut and try type of antenna building. The info collected so far is at least a starting point for the conversion of this antenna. Thanks to all who have given input, it is greatly appreciated. Mike VK3XL -- VK3XL Hello Mike, In your case, I would try to rebuild the ringo. The construction is not that difficult and the capacitance between the radiator and support is designed to provide the right capacitance for doing the matching. To get your whip to resonate as a half wave, you need that capacitance for making the step from 50 Ohms to about 1500 Ohms (also when using the series coil solution). Instead of aluminum strip, you can use heavy copper wire. The ringo gives you the freedom to change the inductance (smaller/ shorter ringo) and the tap. Because of the DC short it gives some protection against the high energetic LF components in nearby lightning strikes. Disadvantage is the somewhat less useful bandwidth. http://www.ea8zq.com/ant27.htm gives some info, the text is Spanish, but the images are nice. http://www.elettronia.it/Catalogo-d.asp?cod=A052 shows a picture of a ringo antenna (Italian site). The ringo has about 2 turns. Somebody living close to me had also a ringo antenna (with about 2 turns). The antenna could be tuned at the antenna base by extending a tube downwards. I'm sorry I don't have picture. Best regards, Wim PA3DJS www.tetech.nl |
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