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Design for matching network for end fed whips?
I am wanting to experiment making vertical whips, end fed, for a number of
frequencies from HF through to UHF and was wondering if someone can point me to a link with designs for constructing these. I want to feed with 50 ohm co-ax for convenience, and I think it basically has to resonate at the design frequency, tapped for 50 ohms to feed it and present a "high impedance" to the end of the resonant element. Naturally there will be different designs required for UHF frequencies compared to HF frequencies for mechanical considerations and I guess different matching networks with different Q's will have pros and cons too.. Anyone with some links / info would be greatly appreciated Thanks Nick |
Design for matching network for end fed whips?
"Nick" wrote in message ... I am wanting to experiment making vertical whips, end fed, for a number of frequencies from HF through to UHF and was wondering if someone can point me to a link with designs for constructing these. I want to feed with 50 ohm co-ax for convenience, and I think it basically has to resonate at the design frequency, tapped for 50 ohms to feed it and present a "high impedance" to the end of the resonant element. Naturally there will be different designs required for UHF frequencies compared to HF frequencies for mechanical considerations and I guess different matching networks with different Q's will have pros and cons too.. Anyone with some links / info would be greatly appreciated Thanks Nick This would all depend a great deal on type of antenna you want to end feed, 1/4, 1/2, 5/8, ect. Jimmie |
Design for matching network for end fed whips?
Nick wrote:
[stuff] Here is a link to get you started: http://www.aa5tb.com/efha.html This deals with a 1/2 wave monopole. I have found that 1/2 or 5/8 is where it is at (antenna radiation pattern), and usually end up physically shortening the 1/2 wave ant with a loading coil or helically winding it over the entire shortened length of ant (fiberglass tube, etc., in the 10 meter band about 8 ft.) Regards, JS |
Design for matching network for end fed whips?
Nick wrote:
I am wanting to experiment making vertical whips, end fed,... End fed whips? Is there some other way they are fed? In the middle? At the other end? Am I missing something (and at my age that is likely)? Irv VE6BP |
Design for matching network for end fed whips?
"Irv Finkleman" wrote in message news:BW4ai.6472$xq1.1239@pd7urf1no... Nick wrote: I am wanting to experiment making vertical whips, end fed,... End fed whips? Is there some other way they are fed? In the middle? At the other end? Am I missing something (and at my age that is likely)? Irv VE6BP Good points guys... ( I guess a vertical dipole could be fed elsewhere ( centre / 1/3rd of the way up etc.... ) I elaborate... End fed half wave dipoles was the original intention, but as JS remarked, an end fed 5/8ths seems more interesting..... One of my applications is for an aerial mounted on a motorcycle windscreen, fed with 50 ohm co-ax for inter-bike comms... 70 cms (or possibly 2 mtrs) but needs to be ground plane independent, hence the thought of a half wave ... Another is a 16 foot whip for 10 mtrs ....... probably mounted just under the house gutter I just want to make myself something for the interest rather than buy something Thanks, Nick |
Design for matching network for end fed whips?
On 7 jun, 23:50, "Nick" wrote:
I am wanting to experiment making vertical whips, end fed, for a number of frequencies from HF through to UHF and was wondering if someone can point me to a link with designs for constructing these. I want to feed with 50 ohm co-ax for convenience, and I think it basically has to resonate at the design frequency, tapped for 50 ohms to feed it and present a "high impedance" to the end of the resonant element. Naturally there will be different designs required for UHF frequencies compared to HF frequencies for mechanical considerations and I guess different matching networks with different Q's will have pros and cons too.. Anyone with some links / info would be greatly appreciated Thanks Nick Hi nick, When you want to be ground plane independent, a halve wave resonance is the best option. It does introduce ground currents, but far less with respect to 1/4 or 5/8 WL. Please note, that you still need some ground, but a motor cycle frame will be sufficient. When you want to have full benefit of the HW, you must assure that it resonates as a half wave (so it will be shorter then an physical half wave). I would recommend familiarizing yourself with an EM simulation program. It may save you a lot of experimenting (with negative results). While the center fed impedance of a HW dipole is not strongly depending on thickness of radiator, the end fed impedance is. An HF whip (5m for 10m) will be somewhat below 1 kOhm, however a UHF thick whip (5mm/70cm band) over a small groundplane will be in the 500 Ohms range. The disadvantage of the HW end-fed is his length. When you want to make it shorter (for example the coil or helix construction), its end- fed impedance increases significantly. When you halve the length (but keep halve wave resonance), you may expect a factor 2...4 increase in impedance. About matching. Mechanically, end-fed matching is easiest, you can put the ground to the motor cycle frame. Elevated feeding gives low feed impedance, but you also have to include a common mode (balun) function. For end-feed, you may use an LC section (L in series with coax, C parallel to antenna), wound transformer, or combination of both. I assume that you have some means to measure VWSR and or impedance and don't touch the ends with there is relative high voltage.... Best regards, Wim PA3DJS |
Design for matching network for end fed whips?
"Nick" wrote in message ... "Irv Finkleman" wrote in message news:BW4ai.6472$xq1.1239@pd7urf1no... Nick wrote: I am wanting to experiment making vertical whips, end fed,... End fed whips? Is there some other way they are fed? In the middle? At the other end? Am I missing something (and at my age that is likely)? Irv VE6BP Good points guys... ( I guess a vertical dipole could be fed elsewhere ( centre / 1/3rd of the way up etc.... ) I elaborate... End fed half wave dipoles was the original intention, but as JS remarked, an end fed 5/8ths seems more interesting..... One of my applications is for an aerial mounted on a motorcycle windscreen, fed with 50 ohm co-ax for inter-bike comms... 70 cms (or possibly 2 mtrs) but needs to be ground plane independent, hence the thought of a half wave ... Another is a 16 foot whip for 10 mtrs ....... probably mounted just under the house gutter I just want to make myself something for the interest rather than buy something Thanks, Nick My trick for feeding a 5/8 is to wind the coil with an 1/8 wl of wire as a starting point and then trim from there. Using the coil in seies with the antenna with coax connected between the other end of the coil and the ground plane(no taps, coil does not conect to ground). This provides a petty decent match to 50 ohm coax that can be reined a bit by drooping your counterpoise(radials). |
Design for matching network for end fed whips?
Thanks for the last two very useful replies...
The desired location for the bike aerial is lower part stuck to the inside of the screen with as much as high and above the screen as possible. The reasons for this are obviously its good to have it as high as reasonably possible, but also to get it away from the QRM generated by the electronics around the dash area. Also, as we ride as a pair, one is always in front or behind the other, so immediately there is the body mass in the way, screening the signal. Now this doesn't generally matter as we are usually withing 200 metres of each other and 1/2 watt at UHF is still full strength signal, but when we get perhaps a few miles apart and are in front / behind situation, the body is definitely attenuating the signal significantly. Generally one rides in front much of the time, so a rear aerial gets round this, and a front aerial on the following bike is not shielded by the riders body - I have both front and rear aerials and I guess it would be good to have an antenna switch to select, but BNCs and swopping is no trouble. The other thing is that everything has to be waterproof where it matters. I have been experimenting with hot melt glue to pot up connections - anyone have experience of this as a good potting agent ? I will put out a separate thread about this as its a bit hidden in this thread.. Thanks again all - much appreciated Nick |
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