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 Post subject: Transmatch?
PostPosted: Feb Mon 12, 2018 9:34 pm 
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OK! I passed the Technician and General exams, and now begins the fun of setting up a station. There's a lot of cool stuff on Ebay, especially Old stuff. Trying to be careful not to wind up with a useless pile of junk.

The ponderment at the moment is about Antenna Tuners, SWR, Watts, and/or Dummy Load. I saw something called a KW 107 Supermatch Antenna Tuner / Dummy Load, which seems pretty cool, kind of an "all in one". Or, you can buy them separately.

One thing I can't figure is - what's all this about "antenna matching"? A matching network at the output of the xmitter feeding the feedline won't exactly match the antenna. Not sure why it's even there - seems like you just connect your 50-Ohm transmitter output to a 50-Ohm coax, and you're done. It's pre-matched. It seems far more likely that the feedline won't match the antenna. If matching is required, wouldn't this be the place?

Can somebody please clear this up? I'm probably missing something obvious.

Thanks!
Phil


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 Post subject: Re: Transmatch?
PostPosted: Feb Mon 12, 2018 9:51 pm 
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Joined: Jun Mon 24, 2013 3:00 pm
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Location: Champaign IL 61822
The gotcha is that the antenna will really exactly match, at best, at one frequency.

Yes, its best to put at match at the antenna. But if you like to tune around,
especially on 80 meters, you need to adjust the match with frequency. That's
tough if your antenna is on a tower. So, if you transmitter can't do it alone,
you will need some matcher at the transmitter even if the antenna is
perfectly matched at one frequency.


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 Post subject: Re: Transmatch?
PostPosted: Feb Mon 12, 2018 10:17 pm 
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philtronics wrote:
One thing I can't figure is - what's all this about "antenna matching"? A matching network at the output of the xmitter feeding the feedline won't exactly match the antenna. Not sure why it's even there - seems like you just connect your 50-Ohm transmitter output to a 50-Ohm coax, and you're done.
The rig might be 50 ohms, and the feed line might be 50 ohms, but the antenna itself will only be somewhere near 50 ohms at some frequency and not at all frequencies.

In the olden days (shortly after the Civil War), the tube type transmitters and transceivers all had to have matching circuits in them anyway because there was a required transformation from the tube impedances (thousands of ohms) to the antenna impedances (generally under 100 phms).

So essentially a transmatch "of sorts" was integral to the transmitters (Load and Tune controls working in concert with a band switched inductor).

With the advent of solid state transceivers there were a lot of "fixed tuned" radios that were designed to deal with 50 ohms period. They would tolerate maybe a small SWR, but often complained and reduced their output power to save the output transistors from damage.

These days there are becoming an increasing number of solid state radios with some degree of internal automatic matching to avoid some of these difficulties.

During this whole process people produced Transmatches, Matchboxes, Antenna Tuners, whatever you want to call them that would allow extremely unmatched antennas to be able to accept power on virtually any frequency. These could be used with radios that had built in turners and radios that had no tuners whatsoever.

The bottom line is that an antenna does not have to be 50 ohms to radiate. Instead, you need an efficient way of converting from the impedance of the radio to whatever the impedance of the antenna many be. The hitch in all of this is the feed line.

Coaxial feed lines present the lowest losses when they are match to 50 ohms at each end. If the impedance presented by the antenna is not 50 ohms the losses in the feed line increase even if a tuner is allowing the transmitter to dump power into the feed line. This leads some to "open wire feed lines".

Open wire feed lines can accept extreme mismatches of impedance without significant loss, but they are not terribly convenient (you have to deal with a feed line that has to be kept away from metal things and can present a shock hazard if not installed properly.

I myself use an automatic tuner to allow me to use a 80/40 meter inverted Vee antenna all across the 3.5 to 30 MHz spectrum with an SWR that is acceptable to a solid state radio that contains no tuner itself. It is a compromise, but it works.

In point of fact even an 80 meter inverted Vee antenna that is 50 ohm resonant at 3.750 MHz may exhibit an SWR significantly above 3:1 at 3.5 MHz and at 4 MHz and may require a tuner just to cover the entire 75/80 meter band with some radios.

Curtis Eickerman

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Last edited by Eickerman on Feb Mon 12, 2018 10:47 pm, edited 1 time in total.

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 Post subject: Re: Transmatch?
PostPosted: Feb Mon 12, 2018 10:29 pm 
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Location: Colorado Springs, CO
It depends if you are going to use resonant or non-resonant antenna. For a long wire (non-resonant) you will need the antenna tuner to match the impedance of the long wire (what ever it may be) to the 50 ohm output of the transmitter. If you use resonant antennas, like a dipole, which is cut for a particular band (80, 40, 20, ect.) and fed with 50 ohm coax, (the impedance at the center feed point of a half wave dipole is approximately 50 ohms give or take a few) then you can get by without the antenna tuner unless you plan on attempting to operate from on end of the band to the other. You usually cut a dipole for a particular portion of the band where you wish to operate. For example, if you wish to primarily operate in the phone portion of 40 meters you would cut the dipole to resonate somewhere around 7.2 mHz.

Bill - K5MIL


Last edited by Bill Harris on Feb Mon 12, 2018 10:44 pm, edited 1 time in total.

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 Post subject: Re: Transmatch?
PostPosted: Feb Mon 12, 2018 10:31 pm 
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Think of it like this--your antenna is everything connected to the antenna jack outside of the radio. It is the feedline (50 Ohm), the actual antenna itself, the tree next to the antenna, the bird sitting on the antenna, the ground below the antenna--everything. The antenna, the feedline, and the ground contribute the most, but it is everything. The SWR meter (or antenna analyzer) will tell you if it is a brick wall you are trying to broadcast into or a soft pillow. A brick wall and you ruin your transmitter. A soft pillow and you don't ruin your transmitter, but you may or may not be broadcasting any signal. A dummy load is a soft pillow--it just won't reach the outside world. I have all sorts of different transmitters and I always use an antenna tuner right at the transmitter. MFJ 949E is a cheap one with dummy load and SWR meter built in. When I first became a ham a few years ago, I started with a Yaesu FT 897D. This is an all mode (CW, AM, FM, USB, LSB, digital, etc.), all band, 100 watt transmitter that is very compact and runs on 12VDC. It receives all frequencies between the BC band up to UHF. It was a good way for me to learn what I liked. I now use it as my camping radio and run it off batteries and a solar panel when I camp.

The next radio I got was a Kenwood TS 830S. From there, I bought some Collins S line, then Drakes, then everything on the planet. I started on this hobby late, but I am making up for lost time.

Norm

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 Post subject: Re: Transmatch?
PostPosted: Feb Mon 12, 2018 11:35 pm 
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Good stuff here - and you may not need a transmatch if your radio has a pi network.
What type of antenna are you planning to use?

A local club can guide you as well; I didn't join a club right away and had some hard knocks in the beginning. Clubs can also be a good source of components to get you up and running.
Keep reading, look at the forums on QRZ.com - many answers there.

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 Post subject: Re: Transmatch?
PostPosted: Feb Tue 13, 2018 3:44 am 
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Phil,

The "all in one" accessories like that KW transmatch seem pretty cool but they tend to be the most expensive way to acquire needed items because in the case of vintage gear these combined setups tend to be less commonly found and thus higher priced AND many contain items you want need or may not want combined into one.

A decent watt meter and a good dummy load are two things that will be useful from the very start and you won't regret getting them. You don't need extreme accuracy for the watt meter and a decent working Heathkit, Drake, Swan, Dentron, etc. will be fine and most can be calibrated fairly easily when you feel the need for better accuracy. Although the watt meter isn't absolutely necessary it is so handy to have that it is a good item to acquire from the start. Being able to simultaneously monitor final amplifier plate current and power output makes transmitter tune up easier and you develop an intuitive understanding of the process being able to monitor both input and output simultaneously.

A dummy load makes you a better "ham citizen" by avoiding creating needless interference while testing your transmitter and it very importantly takes away a source of unknown when you aren't sure if a problem lies in your transmitter, antenna, or external matching network. Going directly to the dummy load takes many of the variables out of the equation.

I got my license back in 1975 and used a Johnson Valiant to feed a 40 meter inverted V for 40 and 15 meters and I shorted the center and shield of the coax together and fed it as a top loaded T on 80 meters. The built in wide range matching network in the Valiant allowed it to easily load into this antenna on all three of the then most commonly used novice frequency ranges. But the SB-102 I acquired shortly after getting a general required a better matched antenna and when I got it I put up dipoles for 40 and 80 and a three element quad for 20-10 meters. I didn't buy my first transmatch (a Tokyo Hy Power legal limit tuner) until I bought a Yaesu FT-980 in 1983 because the Yaesu was very particular about what it fed.

Today my primary antenna for my vintage gear is a full wave 80 meter horizontal loop fed at one corner with coax and I use a homebrew heavy duty reversible L network consisting of the roller inductor out of a Gates broadcast transmitter, a vacuum variable capacitor, and the tap switch out of a BC-375 transmitter to choose on which side of the inductor the capacitor resides allowing it to match both high and low power loads. This setup easily matches my antenna on all bands and will easily handle the legal limit continuous duty in any mode. Parts were picked up at a hamfest and total cost with chassis and turns counters for the inductor and capacitor were under $150.

If you start out with a vintage transmitter that has a wide range matching network you probably won't need a transmatch if your antennas are reasonable. I like using the L network because it also acts as a low pass filter which reduces transmitter harmonic radiation which was pretty high with a lot of vintage rigs.

And definitely follow Smooth Oscillator's advice about looking up a local club. The right advice from someone who can help you in person is invaluable in getting your ham hobby off to a fun start.

Rodger WQ9E


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 Post subject: Re: Transmatch?
PostPosted: Feb Tue 13, 2018 4:31 am 
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Location: Michigan, 49712 - SC, 29577
I had the KW-109 tuner which is similar.

They are classic Z-match, link coupled tuners ideal for using with balanced transmission lines (ladder line, twin lead, open wire) They are well built, definitely superior to any MFJ tuner I ever owned.

If the price is reasonable, I'd grab it.


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 Post subject: Re: Transmatch?
PostPosted: Feb Tue 13, 2018 5:21 am 
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One thing I like about collecting vintage stations is that you can get elements of the station to match--all be from the same company and be designed to look and work together. When I got my Kenwood TS 830S, I then wanted the tuner, the speaker, the station monitor, the mic, the headphones, to all match and be my station. I thought that was really cool and Kenwood had made some fine components. I still use my Kenwood AT-230 as my tuner connected to all my transmitters at my main station. It is rock steady and rarely needs even a small touch-up. It has the wattmeter built in and some switching features.

Norm


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 Post subject: Re: Transmatch?
PostPosted: Feb Tue 13, 2018 7:58 am 
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Greetings to Phil and the Forum:

Phil asks:

Quote:
It seems far more likely that the feedline won't match the antenna. If matching is required, wouldn't this be the place?


I don't think this question was addressed directly, so I will answer with emphasis. Yes, you are correct... this is the place to put the tuner. There are some antenna tuners designed to be placed at the feed point of the antenna. This can be mechanically difficult in the case of dipoles (since you have to support the weight of the tuner in the center of the antenna, you might as well turn it into an inverted V) and it is expensive; these tuners have not been on the market for a long time and are thereby difficult to acquire used.... and priced accordingly. Additionally, most of these tuners have a limited range of impedances they can match... so it is easily possible to find a frequency where your antenna will not work at all.

It is far more practical to place the tuner in the shack.... this way, the transmitter sees the 50 ohm resistive load it is expecting and as for the antenna system, well... it is what it is.

An alternative is to use an antenna system where the feed line is an integral part of the antenna. For example, a long wire directly connected to a tuner designed to accommodate same. This approach minimizes losses in the feed.... such losses as are present are mostly radiative losses... which is what you want.... after all, the device is an antenna, which by definition is supposed to radiate.

Most people do what Curtis, Rodger and others are suggesting.... make the antenna as close to a match as possible on the frequencies of most interest and tune out the reactance (and accept the losses) everywhere else. That's what I do.

73,

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 Post subject: Re: Transmatch?
PostPosted: Feb Tue 13, 2018 8:13 am 
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Thanks everyone, for the awesome comments. At this point it's more of an equivalent-circuit question. The feedline is already matched to the transmitter output, so some kind of matching network in this location could only mis-match it - but is this how you get the feedline to match the antenna, from the other end? Something like that.
Best rgds
Phil


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 Post subject: Re: Transmatch?
PostPosted: Feb Tue 13, 2018 3:18 pm 
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Greetings to Phil and the Forum:

I think we need to dip into transmission line theory just a bit to answer your question:
Quote:
The feedline is already matched to the transmitter output, so some kind of matching network in this location could only mis-match it - but is this how you get the feedline to match the antenna, from the other end?


You seem to be laboring under the misapprehension that because the 50 ohm line is designed as such, that that value is what is presented to an apparatus connected to it. This is not the case.

The impedance that a device (in this case your transmitter) "sees" in looking into a 50 ohm line is 50 ohms if and ONLY IF the line is terminated in a pure resistance of 50 ohms on the other end.

Since we are in agreement that the antenna is probably not going to look like a pure 50 ohm resistance, then we can be pretty sure that the impedance looking into the line will not be 50 ohms either. For reactive loads or resistive loads other than 50 ohms, power is reflected from the load back down the line. This reflection results in voltage standing waves along the line. The greater the mismatch, the more energy is reflected. The reflected energy interferes (I use the physics meaning for interference here) with the incident energy. At some points along the line, this interference is constructive... i.e. the voltages add to produce a higher voltage. At other points on the line, this interference is destructive... i.e. the reflected energy cancels some of the incident energy and the voltage at these points on the line is lower. The ratio of these two voltages is known as VSWR or Voltage Standing Wave Ratio. Often, the V for voltage is dropped and just SWR is used. The VSWR is a measure of the degree of mismatch presented to the line by its load.

The worst case is either an open or a short. For either of these conditions, the termination (either open or short) appears again every half wave down the line, and its opposite appears every quarter wave. For example, a shorted 1/4 wave coaxial line appears as an open on the other end. An open (unterminated) 1/4 wave line looks like a short at the other end. This is the basis of the "stub" filter.... simply a piece of coax "T"ed into a transmission line and cut to the wavelength of an interfering signal. The interfering signal "sees" a short across the line and is greatly attenuated. The signal of interest, if far enough away from the interfering signal in frequency, does not "see" this short and travels on.

It follows that if a 1/4 wave piece of transmission line is shorted at the far end, then its impedance will be near infinite at the near end. Now, if we connect another 1/4 wave piece of transmission line to the near end and go to the end of it, it is seeing near infinite impedance where we connected it to the first piece. Therefore, since a 1/4 wave line "inverts" the impedance mismatch, the inverse of open is shorted.... so after two 1/4 wave pieces, we are back where we started... either open or shorted.

The practical result of all this is that when the transmission line is terminated with an impedance which does not match its characteristic impedance, the impedance constantly changes depending on where you measure it on the line. It goes through maxima and minima periodically along the line. If you happen to choose just the right spot and connect your transmitter there, for one frequency, that spot will be 50 ohms.

This is true ONLY for lengths of line that happen to have a "magic length" determined by the degree of mismatch and the operating frequency. This is where the infamous "How long should my coax be?" question that CB-ers often ask comes from. What they are really asking is how long should the matching network be to match my antenna to my radio on this channel? Of course, if the antenna is a reasonably good match as it is supposed to be, the question should be answered: "Long enough to reach the radio".... because in that case, it doesn't matter.

Because hams operate on a wide range of frequencies and often with imperfect antennas and with random lengths of feedline, the impedance at the end of the transmission line that appears in the shack is a crap shoot. Hopefully it is not so far off as to be hopeless, but it is a rare case indeed when it is 50 ohms resistive. So, in order to transform whatever impedance appears at the transmitter end of your feedline to a 50 ohm resistive load at the transmitter output port, an antenna tuner is required.

Since reflected power in the coax represents loss, the ideal location for the tuner is at the load end of the feedline. For a single frequency, this "tuner" can simply be a carefully tuned matching network, such as a gamma match. For frequency agility, a controllable matching network is required. The best way to implement this is to put an expensive remotely controlled or automatic antenna tuner at the antenna feed point. The cheapest and most practical way is to put the tuner between the feedline and the transmitter in the shack and just live with whatever coax losses this scheme results in. As I said before, this is what most of us do.

Edit: Something that I forgot to mention is that when we are dealing with transmission line, the wavelength is different than the wavelength in free space. For 40 meters, a 1/4 wave is roughly 33 feet in air.... but it is only 22 feet in most coaxial cables. This is due to the Vp or Velocity of Propagation of the wave down the transmission line as opposed to free space. Most coax cables have a 'Velocity Factor" of 66%. This means that the velocity of propagation of the wave in the cable is 66% of the velocity in free space, which is c, or the speed of light.

Regards,

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 Post subject: Re: Transmatch?
PostPosted: Feb Tue 13, 2018 4:51 pm 
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Assuming that you will want to operate on more than one ham band you will need to make a few basic antenna decisions.

Lets say you want to work 80, 40 and 20 meters with dipole antennas

If you decide on a 50 ohm coax feed line, you will need to erect three separate antennas. The 80 meter antenna will not cover the entire band without higher than necessary feed line loss in your transmitted signal as you tune from the design frequency of the dipole. This is a problem hams have been struggling with for decades. Many, many articles in the ham magazines have been dedicated to it. Also you will be limited to these three bands. No 30 meters, no 17 meters, no 12 meters and no 10 meters. Some guys use their 40 meter dipoles on 15 meters with less than optimum results.

Alternatively you can use one antenna, a 130' +/- doublet, low loss transmission line like 600 ohm open wire and an antenna tuner, at your operating position, between the radio and the feed line. If you go this route you'll be able to operate on all bands from 80- 10 meters with relatively low losses. A balanced tuner (like the KW) is best in this scenario.


http://trueladderline.com/80-10-meter-w ... -feedline/


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 Post subject: Re: Transmatch?
PostPosted: Feb Tue 13, 2018 5:52 pm 
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W8EJO wrote:
If you decide on a 50 ohm coax feed line, you will need to erect three separate antennas.
Not exactly.

http://www.hamuniverse.com/4bandmaypoleantenna.html

http://www.hamuniverse.com/multidipole.html

I've used variations of these for almost 54 years.

Yes, they technically are multiple antennas, but they use only a single coaxial feed line, so they are not exactly separate.

I still needed an antenna tuner to get under 2:1 over the entire 75/80 meter band because of the wide percentage bandwidth required (13%) compared to the other bands.

My current antenna is just an 80/40 meter version with an antenna tuner helping out on 80 and the other bands. I miss my 3 element TH-3Jr beam which is disassembled and sitting in the garage because of a deed restriction (no HOA, but a similar problem).

Curtis Eickerman

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 Post subject: Re: Transmatch?
PostPosted: Feb Tue 13, 2018 6:24 pm 
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This is being made far too complicated. String up a wire dipole for which ever band you want to operate, feed it with 50 ohm coax and get on the air. If you want to operate more than one band, either put up other dipoles for those bands or as Curtis E. suggest, make a fan dipole with elements for different bands.

Bill - K5MIL


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 Post subject: Re: Transmatch?
PostPosted: Feb Tue 13, 2018 6:47 pm 
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Eickerman wrote:
W8EJO wrote:
If you decide on a 50 ohm coax feed line, you will need to erect three separate antennas.

Not exactly.
Yes, they technically are multiple antennas,
Curtis Eickerman


Curt
I've read your posts in the past and find them very well written. You are obviously quite knowledgeable.

However ....

Your first example [http://www.hamuniverse.com/4bandmaypoleantenna.html] requires nine (9) supports, or if erected as lower efficiency inverted V's, a jungle of trip wires in the back yard.

The second example [http://www.hamuniverse.com/multidipole.html], a classic fan dipole also has disadvantages. There will be interaction between the dipoles unless the physical and frequency separation is adequate. This means 40/30, 20/17, 15/12 will be problematic. Even 80, 40, 20, 10 becomes unwieldy and heavy/saggy. An all band (80/75, 60, 40, 30, 20, 17, 15, 12, 10 meter) version is really not doable.

All of these issues are eliminated with the open wire fed 130' doublet. All bands, two supports, low loss, no radials.

What other antenna can do that?


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 Post subject: Re: Transmatch?
PostPosted: Feb Tue 13, 2018 8:02 pm 
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W8EJO wrote:
Your first example [http://www.hamuniverse.com/4bandmaypoleantenna.html] requires nine (9) supports, or if erected as lower efficiency inverted V's, a jungle of trip wires in the back yard.
As I said I used variations on the idea. My support was a guyed 35 foot push up mast at the peak of a home (topped out around 55 feet). No I did not have "perfect angles" which are not required. Only two supports were needed that were attached to a fence and terminating about 10 feet above ground. All the other antennas terminated at tie points on the roof. Zero tripping hazards (caution was required walking on the roof, but caution is always required when walking on a roof). The center point was raised via a pulley at the top of the pole so that maintenance was a non-issue.

With regard to interaction between antennas, yes their is some. So initial tuning of antennas can be a little tricky (30, 17, and 12 were not available bands at the time either). On the other hand, once done, except for 75/80 I had under 2:1 VSWRs on all other bands across each band. The VSWR going above this on 75/80 had nothing to do with interaction. The issue on 75/80 meters was simply a matter of the percent bandwidth for an Inverted Vee at this frequency.

I operated 80/40/20/15/10 for years without any external tuner. Eventually added a 3 el beam for 20/15/10.
W8EJO wrote:
All of these issues are eliminated with the open wire fed 130' doublet. All bands, two supports, low loss, no radials.

What other antenna can do that?
Well actually several, but they all have their issues too. At the same time the tuned feeders on a doublet with 2 tall supports is not without its issues either (I did not have to route tuned feeders, only required 1 tall support, and still had adequate multiband operation). The issues are just different ones. Every antenna has them. It just depends on if those issues are a deal-breaker for a particular installation or not. For me, having 2 tall supports 130 feet apart was not an option unless I put the supports in the neighbors back yards.

Antennas don't have to completely adhere to strict rules to be effective and adequate. For example, my inverted Vee on 75/80 was not completely vertical. Did that actually make a difference? In reality, it did not for my particular use. It was also not intended to be a DX antenna. If it had been for DX a different antenna would have been a better answer (the reason for my eventual beam on 20-10).

Please understand I am not saying my antenna was THE best answer. It was just MY answer to the constraints I was faced with and the issues I was prepared to address.

My current antenna is much worse in many respects. However, I need to keep it at a height low enough no tend to inhibit anyone going to the trouble to complain about it and be relatively inconspicuous. The one neighbor that actually noticed it thought I was putting up something for Christmas lights because I put it up in December. Then they wondered why there were never any lights on it. :D Now there's a thought!

Curtis Eickerman

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 Post subject: Re: Transmatch?
PostPosted: Feb Tue 13, 2018 9:06 pm 
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Thanks everyone, for your insights! Looks like there are several different ways to go. Theory-wise, as usual, I was trying to oversimplify the situation. Haven't given it a thought ever since that microwaves class about 40 years ago.


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 Post subject: Re: Transmatch?
PostPosted: Feb Wed 14, 2018 1:30 am 
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I now use a balun fed dipole on one band. Cut so that it sort of favors one end of the band but most of the band has a low SWR. Previously I used a dipole center fed with window line, an open wire feeder that is similiar to ladder line. I did not nitpick the exact antenna length as I used a tuner with it and basically could tune it perfectly flat on any part of the band, and being an MFJ tuner, it had the crossed needle meter that made for fast adjustments. That is if you don't mind the bother of tweaking it constantly if you change frequency to transmit. It could also be retuned for use on other bands with a flat match to the radio, and the feedline losses were probably pretty minimal as compared to coax with a mismatch. Or you could just buy an autotuner, and let it get the best match quickly for you. I think most of those are not set up for use with balanced lines, though.

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 Post subject: Re: Transmatch?
PostPosted: Feb Wed 14, 2018 2:36 am 
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Do away with coax cable! Open wire feeder fed from the balanced output of your shack tuner and all is good - just what was done in the 50's - the tuner then tunes the antenna and the feeder - you can't make 50ohm coax into anything else with a tuner - you may end up getting a very large voltage node somewhere down the coax and - poof.

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