Antenna tuner/ground plate

[Seeking Solace]

Originally Posted by ka4wja

Osprey,
Please read Jim Cate's posting....
And, please read the recent discussion I referenced...
And, please forget the BS about needing a resonant antenna or antenna tuner to receive HF signals...

Do, all of those.
Tell us exactly where you are at, what you wish to receive, and at what time of day....and we'll get you going...

fair winds...

John

John, sorry to say after all these years of playing radio you've let some book somewhere tell you that resonance is hogwash for reception. I respectfully disagree. Try doing a S/N reading on a non resonant antenna vs a resonant antenna and the results will be immediately obvious. Does it need to be absolutely resonant, no. I believe I stated that. I also stated that it was a compromise with any antenna installation.

I can also say that you can not use your watt meter to calculate signal loss based on input vs output. You would have to measure input vs output directly. Your watt meter doesn't take into account velocity factor of cable, inherent connector losses, or any of the other factors that can and do add up. Nothing you said added to the conversation in any way.

Perhaps you feel it is your need to try to correct everyone on the internet? It's radio theory as I've told you in other posts. There is no exact science to it or it would be called radio fact. There are literally thousands of publications and practical application studies that prove the benefits of resonance. It is also a scientific fact that when capacitance and inductance match you have resonance and the least resistance to the transfer of energy in RF circuits.



How long you've been repeating unfactual opinions about RF and db loss is of no consequence, I use this "theory" everyday to communicate via HF, VHF, and in multiple modes. I possess the exact same license you do and took a very likely similar proctored exam administered by qualified examiners. Calling my observations, and that of many other qualified RF engineers "Hogwash and BS", while your opinionated right, is rude regardless of your intentions.

I would like you to show some pier reviewed technical information that would say that a resonant antenna is not more effective than a non resonant antenna. I believe you will not now or ever find such a mythical document. That is your experience, and I can respect that, however it is wrong.

[Paul Elliott]

Antennas do not have to be resonant to function well. A tuner or matching network may improve the received signal strength, but usually not enough to matter in the real world. As John says above, if you can hear the noise level increase when you plug in your antenna that's usually all the antenna gain you need. Most SSB receivers have plenty of available gain.

One factor that can make a (usually small) difference, is that a resonant antenna is usually going to be somewhat directional. All antennas are directional to some degree, other than the theoretical isotropic antenna. If this directionality favors the signal you are trying to receive, then that signal will be stronger and the noise from the non-favored directions will be reduced. This can give you a few dB of signal/noise ratio improvement. In most cases you won't notice it.

Antenna gain, impedance matching, cable and connector loss, transmitter power, all are very important on the transmitting side of the connection. Every dB of loss or gain here directly affects the received signal-to-noise ratio.

Interesting sidetrack: I was experimenting with milliwatt-level radio propagation (see WSPR), and I was using a 50 db attenutator in my receiver input. This let me monitor my transmitter output without overloading the receiver. Even with this 50 db loss my receiver was still picking up some distant WSPR stations. I don't recommend putting a 50 db attenuator in your receiver connection, but this reminded me that most of the time antenna gain isn't all that important for reception.

[Seeking Solace]

Originally Posted by Paul Elliott

Antennas do not have to be resonant to function well. A tuner or matching network may improve the received signal strength, but usually not enough to matter in the real world. As John says above, if you can hear the noise level increase when you plug in your antenna that's usually all the antenna gain you need. Most SSB receivers have plenty of available gain.

One factor that can make a (usually small) difference, is that a resonant antenna is usually going to be somewhat directional. All antennas are directional to some degree, other than the theoretical isotropic antenna. If this directionality favors the signal you are trying to receive, then that signal will be stronger and the noise from the non-favored directions will be reduced. This can give you a few dB of signal/noise ratio improvement. In most cases you won't notice it.

Antenna gain, impedance matching, cable and connector loss, transmitter power, all are very important on the transmitting side of the connection. Every dB of loss or gain here directly affects the received signal-to-noise ratio.

Interesting sidetrack: I was experimenting with milliwatt-level radio propagation (see WSPR), and I was using a 50 db attenutator in my receiver input. This let me monitor my transmitter output without overloading the receiver. Even with this 50 db loss my receiver was still picking up some distant WSPR stations. I don't recommend putting a 50 db attenuator in your receiver connection, but this reminded me that most of the time antenna gain isn't all that important for reception.

Picking up stations with a 50db attenuator is no surprise. Even on a dummy load I can easily get into a repeater that is about 5 miles from me with 500mw.

A lot of people discount that mismatch on RX antennas. When 1db of signal can mean the difference between intelligibility and indiscernible signals that loss on the receive can make a big difference. (Weather fax is not a weak signal in my experience by any stretch. I've had to attenuate the signal to prevent overload in my receiver)

My observation is that a well matched antenna can greatly reduce reception of spurious signals and unwanted RFI. If the RFI is close to the operating frequency that you are working you can actually even get better results detuning the antenna. It's a catch 22 any way you look at it. I use another piece of equipment that nulls everything that is not wanted by shifting and adjusting the audio frequency after it's been demodulated. It's very effective for CW and Phone work, but an expensive addition to any station.

Let's assume that the antenna is a 50 ohm antenna and the first stage of the receiver is also 50 ohms. We both know that isn't remotely likely, but for the sake of doing the math we need to have a starting point. Now, let's present a mismatch at the antenna between 50 and 75 ohms.



Source Impedance:
50
Ohms Absolute Load Impedance:
90.14
Ohms
Load Impedance R:
50
Ohms Load Reflection Coefficient:
0.6
Load Impedance J:
75
Ohms Load VSWR:
4
Load Return Loss:
4.44
dB
Load Mismatch Attenuation:
1.938
dB

Now we're going to do that again going from the F connector back to the receiver. We can double our load mismatch calculation of 1.938 x2 = 3.876db of loss in the antenna system. Yes, it's understood that without common mode the loss is less important, but it is still there.

What happens to that signal that comes into the antenna that is reflected by the mismatch condition? It gets radiated back out just like any RF signal would be reflected to a mismatch antenna from a transmitter. Unlike a transmitter that will continue to supply a fresh source of RF, the receiver can only get what it is able to pull from the air. It is a much weaker signal too!

So what the end result presents to the amplifier stages of the receiver is all that much weaker. Now what that means to us is that our "Signal" will be much smaller as compared to our "Noise" (S/N ratio). If the RX signal is greater than that of the noise then it's not an issue. The closer those two numbers get to one another the harder to get anything useable into our amplifier stage it is going to be.

That's just the impedance mismatch. It doesn't take into effect the loss from insertion, velocity factor, or any other causes of loss in the antenna system. The reason many commercial receivers don't worry about matching antennas is because they are dealing with a strong enough signal to begin with that is able to overcome any "Noise" they have along with that desired signal.

Since dBm is based on a logarithmic scale, it is an absolute power measurement. For every increase of 3 dBm there is roughly twice the output power, and every increase of 10 dBm represents a tenfold increase in power. 10 dBm (10 mW) is 10 times more powerful than 0 dBm (1 mW), and 20 dBm (100 mW) is 10 times more powerful than 10 dBm.

You can convert between mW and dBm using the following formulas:

P(dBm) = 10 · log10(P(mW))

P(mW) = 10(P(dBm)/10)

For example, a power of 2.5 mW in dBm is:

dBm = 10log2.5 = 3.979

or about 4 dBm. A dBm value of 7 dBm in mW of power is:

P = 107/10 = 100.7 = 5 mW

Path loss is yet another factor you must contend with. As distance increases the loss along your path (or multiple paths) will increase.

TX power + TX antenna gain – Path loss – Cabling loss + RX antenna gain – 10dB fade margin > RX Radio sensitivity or (less commonly) RF noise floor. Things add up quickly. Just because you're able to RX without a resonant antenna doesn't mean it is as good as you would with one, or even that having one will be better in all situations.

I don't know how technical you want to get about it, but you can always take away from a signal by reducing your RF gain on the input. There comes a point that you are no longer able to amplify the wanted signal without also increasing the unwanted products as well. If given the choice, I'll take a strong signal and attenuate it.

He's thinking about putting in an HF radio, not just using the pretty low quality receiver that he currently owns. Putting in a half decent solution will mean starting over later with doing it the right way.

[ka4wja]

Seeking Solace,

I have no idea what you are talking about???
What book???
I never mentioned any book??

I should have never even tried to help..

I'm truly sorry, but...I'm sort of at a loss as to what to say...in my over 40 years of real-world HF comms experience, including design, construction, and operation of dozens and dozens of HF antennas, as well as studying and teaching radiowave propagation and antenna system design for much of that 40 years....I'm still surprised by many who miss the point (all poodles are dogs, but all dogs are not poodles)...
{and, while this does contrast with my professional life (where resonance and infinitesimal differences ARE very important....in the world of HF comm circuits, for HF receiving, these are not important factors at all....and will confuse the issue at hand, which is trying to get Osprey877 to learn how to receive the WeFax and Voice weather info that he needs, and he does not need to use a resonant antenna, nor an antenna tuner....and those are the facts....sorry...}

You know just because one antenna, or another, works for someone, for a certain path, for a certain number of days/years, etc. and you measure its performance and are happy with it....that's great! And, if a particular antenna's pattern matches the most common angles of attack/reflection for these paths, and/or its pattern assists in improving the received S/N, that's great too!

And, I'm happy for you...but...
But, what does this have to do with resonance???

You keep mentioning use of a resonant antenna and/or using an antenna tuner, is better....and for HF receiving, this is total and complete hog wash...
Please forgive me sir, I'm truly sorry, but just because you believe this to be true, and just because others may also believe this, and just because you've found that using a resonant antenna (or a non-resonant one with a tuner) has improved your received S/N, does not change the facts that the underlying statement is false...

There is so much signal (and noise) that the infinitesimal difference that might be calculated, when dealing with a HF comm link, the point is moot....

I do not wish to go 'round 'n 'round on this any more, and I will not....
As I think the only outcome would be contention and hurt feelings, but please sir....please accept what I write here....
I am NOT saying that your experiences didn't happen, just that the conclusions you draw from them are false and misleading, and passing them along as "fact" is quite disingenuous....like I wrote above, it's like you're trying to say that just because all poodles are dogs, then all dogs are poodles, which we all know is not true...


Now, being rude isn't who I am, but just ignoring all of this false info and allowing some of my fellow sailors to be misinformed isn't me either....
Just about everything you write is incorrect....yes, quite a bit of it is thought of as fact by so many of my fellow hams....but total bunk, nonetheless!

Of all of these myths and false info you post....this is the most egregious....

Originally Posted by Seeking Solace

The selectivity and sensitivity of the receiver will determine how good of an antenna will be needed to hear your desired station.

The sensitivity and selectivity of the receiver has nothing to do with how good of an antenna you need, except to say that a really good directional antenna (not possible on our boats) can allow you to null out interfering signals (noise and/or other undesired stations), and possibly reduce interference from stations on an adjacent channel/frequency...

Every HF communications receiver / transceiver made in the past 40 - 50 years (with the possible exception of some $50 made-in-China junk) has more than enough sensitivity to receive HF signals just fine....nobody needs a book or spec sheet to prove it, just turn the receiver on and plug-in an antenna, if the noise goes up (or you get a signal), then it is sensitive enough....(understand that natural background noise on all HF freqs below 20mhz - 25mhz, even in the open ocean and/or quiet rural areas is higher than the sensitivity of any HF receiver!!! And, most HF comm users will use attenuators on all freqs below 15mhz to move the receiver's dynamic range into a more usable range...(or use small, inefficient, but directional, receive antennas, and the excellent sensitivity of our modern receivers....to improve received S/N...)

Maritime HF comms, is fairly uncrowded (unlike the ham bands)....and while most cheap, portable SW receivers don't have adequate selectivity to operate on our crowded ham bands with a good antenna (like using a shroud or stay), on the maritime HF freqs, there are NO issues at all with selectivity.....and even if you were on a crowded band, a resonant antenna (or antenna tuner) does not have any usable "selectivity" to assist the receiver in discriminating adjacent signals....there is no correlation between receiver selectivity and antenna resonance!!!


Again, I'm sorry....but this is all bunk / myth / false info....yes, much of it is propagated my so many of my fellow hams as fact, and I just roll my eyes, and tune away.....but, here I'm trying to get a sailor who appears new to HF comms ("Osprey877") some factual info that will help him....I have no interest in further argument / discussion here....

I have tried to be polite and courteous here, and quite honestly, I'm regretting even trying to help this guy Osprey877!
First you imply that somehow "books" have it wrong and you're right...and then you want me to post a peer-reviewed paper about how a non-resonant antenna can receive signals as well as a resonant one??
Well, I'm 200 miles away from my desk and references....so that's not going to happen...sorry mate!

But, I can refer you to many reference books (radio engineering handbook, ARRL handbook, RSGB handbook, etc.) that you should have easy access to....but, if don't believe in the books, why ask about them??

Seriously, the problem is quite obvious to all of us who have been there and done that, as well to anyone who grasps the facts, not just believes the BS propagated on-the-air and online...
(and, if you want to come off like an ass, that's good....'cause talking about "velocity factors" and "inherent connector losses", makes it clear you really have no clue! )
{BTW, in my professional life (not sailing / not HF radio), I figure link budgets down to the "hundredth of a dB" (0.01dB) and here connector loss IS taken into account....even at microwave freqs, it's typically in the range of 0.05dB in total....but, on an HF comm circuit??? You're really in the weeds there! }

I have absolutely NO interest at all in insulting anyone!!!
And, no....I do NOT think it necessary to correct everything....but, maybe you could look in the mirror, and ask yourself did you give Osprey877 useful info??? (BTW, the answer is no...)
And, please understand that I did struggle with what to write here....I wanted my fellow sailors to have accurate / correct info, but could not figure out how to do that without correcting you...
(you know, when I'm wrong and/or learn something new, I admit it....and actually thank the person who helped me learn....just learned something new yesterday!....just saying if you read what I wrote, I think you'll see it is just factual info, and me trying to help Osprey877...)


My ONLY interest here is to help Osprey877....and just hoping he will read Jim Cate's post above....read the discussion I referenced....tell us about where he is at....
If that's not good enough for "Seeking Solace", well there is nothing more I can do...

Osprey877, please do yourself a favor and read Jim Cate's post above....read the discussion I referenced....tell us about where you are at, where you're planning on sailing, etc....and whether you're in a marina, etc....and assuming we can get you familiar with HF radiowave propagation and use of the Sitex receiver, we will get you going...


Fair winds....and I'm done!!
(seriously, I'm done with this thread and wish you all the best...)


John


P.S. As I reread what I wrote....I do regret getting involved in this discussion....not because I don't stand behind my words, but because I think I stirred up things that distract from Osprey877 getting his system working....
So, I'm outa' here...

[Seeking Solace]

I'm sure that if I had posted that someone was wrong and offered nothing to back up my position it would be easy enough not to reference why.

Osprey, the information is out there and it's free. You don't have to take my word or anyone else's. I've even shown the math to back up my claim and the caveats to go along with it.

Everyone is an expert. I guess I wasted my college money and RF engineering should be a hobby better left to those who've spent 30 years deciding what is fact and what is fiction.

Putting all internet trash talk aside (everyone's smarter online). Just drag that cable over to the chainplate and hold it to it. Make sure you're on a frequency that is appropriate for the time of day and what should be the strongest station in your area. Touch it to it and you'll get the faxes if it is working right. Otherwise, go sailing and have a good time!

The best thing about getting offshore is you don't have to even think about the internet, telephones, or that annoying neighbor down the street.

I don't know if John will be back to this thread, but I wasn't trying to be a jerk. I took offense to what you said. Saying that you don't mean to offend doesn't retract from calling someone outright a liar and propagator of myth. We can agree to disagree. To each his own right? People said the world was flat for a very long time, doesn't mean they were right even if it was being taught. I did assume (I know ass u me) that your knowledge was gathered from technical documentation in a book somewhere. It was a poke that the information contained therein was incorrect.

I like weak signal work. That's why matching is important to me. I still have fun with my crystal radio kit attached to the fence too. If only those weather faxes were in AM I could probably get them in with it too. You're right that none of these last exchanges probably helped him in any way. It's technical information that wouldn't make sense to someone who wasn't in the field or a serious hobbyist. Cheers!

[Jim Cate]

Originally Posted by osprey877

I have a Target SSB Receiver (NOT a transceiver). Do I need an antenna tuner and ground plate, or are they only needed for transmitting, not receiving?

g'Day Osprey,

By now I bet that you are sorry you asked! You have received pages of suggestions, backed by esoteric language and calculations, and I bet that most of it was pretty much over your head and added little to your useful knowledge.

So, here is what I think will be a practical set up and a practical way to check it out.

1. Get rid of the co-ax cable and the adaptor that you now have hooked up.

2. Get a simple phono plug, one that fits into the socket labled "antenna", and solder a length of copper wire, somewhere around 14-18 ga to the center conductor on the connector. Take the other end of the wire to the nearest chain plate or other fitting that is directly attached to a shroud or stay on your boat, and attach it there. Depending on the physical dimensions of that fitting, you may use a ring terminal, fork terminal or alligator clip to make the connection.

3. Now, get the boat out of the marina and away from houses, other boats, overhead wires and industrial sites. Hopefully a mile or so away... but whatever you can conveniently achieve. Then turn off everything on your boat that you can: fridge, instruments, computers and chargers, inverters, solar regulators... everything electrical. And this means in many cases, turning off the supply power at the switch panel. Even better is to simply pull off all the battery positive cables and run a temporary wire to power your radio. These steps will do a fair job of eliminating RFi sources on your boat.

4. Now, turn on your radio and tune it to 5.000, 10.000 and then 15.000 MHz in turn. Depending on the time of day, on one of those frequencies you should be able to hear the WWV or WWVH time signal broadcasts.They are there 24/7, and should be easily heard if the radio is functioning correctly.

5. If you do hear one of those signals, your radio and antenna are working ok. Nt necessarily optimally, but good enough for your purposes. If you can not hear one, then I suspect that your radio is faulty, for the setup should be adequate.

6.Now, start reconnecting the various on board electrical devices that you just turned off... one at a time, checking your reception each time. This will help you identify any RFI sources that may lurk on your boat.. things that you will need to either turn off whilst trying to get your wx, or seek help in cleaning up electrically. Do take notes while doing this!

After this, return to the marina and try again. I suspect that you will have limited success there... I know that I've been stymied by marina noise in most of those we've been in over the years, despite all the clever things I've tried!

Good Luck, mate

Jim

[transmitterdan]

Osprey,

Since there is a bunch of noise in this thread it's hard to find the signal. Such is the internet of things.

Read Jim Cate's post. If you don't have an RCA connector you can just take a long piece of wire and fold it a few times and stick it into the hole of the antenna jack. Don't worry about a ground. Don't force it but fold the wire just enough times so it fits snug. Pull the wire up into the air with a halyard (flag halyard works great). If the antenna is a few meters long it will pick up WWV.

Ignore all the nonsense about resonant antennas. You don't need to know any of that.

When you want to transmit either on ham or marine bands come back here and ask questions. KWJA is a good resource to consult before you buy or install anything.

[Paul Elliott]

Originally Posted by Seeking Solace

A lot of people discount that mismatch on RX antennas. When 1db of signal can mean the difference between intelligibility and indiscernible signals that loss on the receive can make a big difference.

And this is our fundamental disagreement. 1dB of loss at the receive end will have virtually no effect. Neither will 10dB.

At the receiver, the Signal to Noise Ratio (SNR) is what counts. That dB of loss due to an antenna mismatch will attenuate both the desired signal and the undesired noise by the same amount. The SNR will be unchanged. The signal will still be readable, or unreadable. In virtually all cases, if you can hear the atmospheric noise then you have enough gain.

At the transmitter end, 1dB of extra signal will improve the received SNR by 1dB. This is where matching and loss become important.

For what it's worth, I do understand this stuff. I used to design and test commercial VHF transmitters and receivers. At VHF and above, atmospheric and other noise is much lower than what we get on the HF SSB frequencies. Compared to the frequencies being used for marine WFAX, VHF reception is much more sensitive to losses and matching.

[Seeking Solace]

Originally Posted by Paul Elliott

And this is our fundamental disagreement. 1dB of loss at the receive end will have virtually no effect. Neither will 10dB.

At the receiver, the Signal to Noise Ratio (SNR) is what counts. That dB of loss due to an antenna mismatch will attenuate both the desired signal and the undesired noise by the same amount. The SNR will be unchanged. The signal will still be readable, or unreadable. In virtually all cases, if you can hear the atmospheric noise then you have enough gain.

I agree 100% that the mismatch will reduce both unwanted and wanted signals equally. Where I begin to diverge is that at some point the signal will be in the noise floor for any given frequency and conditions.

It is my opinion that by increasing the match by tuning the antenna to the resonant frequency you will have a greater opportunity to keep your desired ratio squarely in the Signal side of the equation. Because of the nature of tuned circuits you are inherently rejecting the unwanted signals that are not resonant with the antenna.

Here is a working example. You've tuned into a station that you want to hear. They have a weak signal (You're antenna is a random length that is not matched to the receivers input impedance). Now, you use your tuner to match the antenna to the radio. You will hear both the "noise" and the station's signal increase, and if equipped see a measurement of the change on the meter. The weak station is now much stronger as compared to the "noise" that is also present. I do this each time I pre-tune for a given operating frequency.

Without tuning those weak stations would not be otherwise able to hear. You're not changing the equipment's S/N ratio when you do this. You're actually getting more of the signal you want to hear and less of the noise that is not resonant on that frequency. You are effectively giving yourself more gain on a specific frequency while rejecting other frequencies. It is a "tuned" circuit.

[Paul Elliott]

Originally Posted by Seeking Solace

[...]

Without tuning those weak stations would not be otherwise able to hear. You're not changing the equipment's S/N ratio when you do this. You're actually getting more of the signal you want to hear and less of the noise that is not resonant on that frequency. You are effectively giving yourself more gain on a specific frequency while rejecting other frequencies. It is a "tuned" circuit.

The bandwidth of any antenna, or impedance-matching tuner, is so broad that it will have no effective noise-reduction effect with a normal radio. The radio's own filters are measured in KHz (usually 3.5 KHz or so), and are extremely sharp and deep. A tuned antenna will have a bandwidth measured in the tens or hundreds of KHz and will be pretty broad.

This tuned-antenna selectivity can help in the case of strong out-of-band interference (which can overload the front-end, causing intermodulation distortion products), but this is not usually a problem on our boats.

Look I'm not saying that losses are good, or that there aren't rare cases where excess loss might reduce readability. I am saying (as are others) that in the OP's case they almost certainly aren't an issue.

[transmitterdan]

Originally Posted by Seeking Solace

Here is a working example. You've tuned into a station that you want to hear. They have a weak signal (You're antenna is a random length that is not matched to the receivers input impedance). Now, you use your tuner to match the antenna to the radio. You will hear both the "noise" and the station's signal increase, and if equipped see a measurement of the change on the meter. The weak station is now much stronger as compared to the "noise" that is also present. I do this each time I pre-tune for a given operating frequency.

Many marine HF transceiver rigs employ an antenna auto-tuner. These are necessary for the transmitter section to work properly. It is likely that if the tuner was previously tuned to a frequency well removed from the desired frequency then it will attenuate this new desired frequency by many 10's of dB making reception difficult or impossible. Therefore, it helps to retune the tuner to the desired frequency. So I can understand why you might get the idea that antenna tuning helps a lot. A better way of thinking about it is that mis-tuning the antenna really attenuates the signal a lot. Even so, no tuning is much better than mis-tuning. One should not take the experience with one type of rig and try to extrapolate it to a completely different one.

[Seeking Solace]

Originally Posted by transmitterdan

Many marine HF transceiver rigs employ an antenna auto-tuner. These are necessary for the transmitter section to work properly. It is likely that if the tuner was previously tuned to a frequency well removed from the desired frequency then it will attenuate this new desired frequency by many 10's of dB making reception difficult or impossible. Therefore, it helps to retune the tuner to the desired frequency. So I can understand why you might get the idea that antenna tuning helps a lot. A better way of thinking about it is that mis-tuning the antenna really attenuates the signal a lot. Even so, no tuning is much better than mis-tuning. One should not take the experience with one type of rig and try to extrapolate it to a completely different one.

I'm not sure I see where you're going with this. I fully understand why and how a tuner that has been tuned to a frequency far away from the desired one would cause poor reception.

Let's take a brief moment and in layman's terms discuss what a tuner does.

A tuner matches the input impedance of two connections to present a matched load to a transmitter or receiver. Typically an LC circuit or some variant of CLC, LCL, LLC or whatever combination of inductance and capacitance it needs to create a balance between inductance and capacitance. When inductance and capacitance cancel one another out you get reactance. This is what happens when we say we have a resonant antenna. It's wavelength and impedance matches the receiver or transmitters desired input or output.

To make that as simple as possible it would be said that it electrically lengthens or shortens the antenna by presenting a matched load to the input or output of the device. This allow the most unhindered transfer of power in both directions.

A detuned antenna is no different than a non resonant antenna. They are one in the same in every way. Any antenna that is not physically or electrically the correct length for a given wavelength signal will induce a standing wave or reject the current applied to it. Tuners are a compromise because they do not actually change the length of the antenna. They only change the load matching. Eventually in theory the energy will be transmitted from a transmitter, despite a mismatch. In the case of a receiver it will reject the current and it will be reflected unless it's path has the least resistance.

This is before it ever makes it to the receivers first stage of amplification. There is a inherent noise floor that exists on every band and is the point that signals below this level are going to get exponentially more difficult to demodulate. If the signal is below this threshold you will not be able to pick it out of the noise no matter how good your signal to noise ratio.

You're experience with a detuned, non resonant antenna is exactly what my original post was about. It is another field confirmation of the same thing.

[transmitterdan]

Originally Posted by Seeking Solace

I'm not sure I see where you're going with this. I fully understand why and how a tuner that has been tuned to a frequency far away from the desired one would cause poor reception.

Let's take a brief moment and in layman's terms discuss what a tuner does.

A tuner matches the input impedance of two connections to present a matched load to a transmitter or receiver.

Not exactly. A tuner transforms the antenna impedance (S11) at the tuner output terminal to the nominal impedance of the transmitter which is connected to the tuner input. But there is no need to impedance match the receiver since the receiver is already presenting 50 ohms to the antenna. There will be little or no reflected signal at the receiver with or without a tuner since it is internally matched. But because marine transceivers have a tuner it is important to get it tuned right so it isn't acting as a big expensive attenuator sitting between the antenna and the receiver. That is what I am getting at.

Originally Posted by Seeking Solace

A detuned antenna is no different than a non resonant antenna. They are one in the same in every way.

They are not the same at all. A non resonant antenna can be a perfectly good receive antenna and yet be a poor transmit antenna. Ask yourself how many receive only receivers you have come across that require resonant antenna tuners? Pretty much none of them do. Television receivers, automobile radio receivers, scanning receivers, etc. do not have resonant tuners. By your reasoning they should not work which is clearly not the case. They work just fine. This is so because whatever power the antenna can collect it delivers to the receiver input terminal. Almost none of that power is reflected back out of the receive port and no resonant tuner is required to make this statement true. All that is required is a halfway decent receiver front end.

I have designed, built and work with some of the largest antennas on earth. I truly do know this subject. For the OP, any several meter long piece of wire plugged into the antenna jack will receive weather faxes and other HF broadcasts just fine. They do not need an antenna tuner.

[Paul Elliott]

Originally Posted by Seeking Solace

[...]
There is a inherent noise floor that exists on every band and is the point that signals below this level are going to get exponentially more difficult to demodulate. If the signal is below this threshold you will not be able to pick it out of the noise no matter how good your signal to noise ratio.

What exactly do you mean by this? Signal and noise define the Signal to Noise Ratio. There is no such thing as a "good signal to noise ratio" independent of the signal and noise levels.

And yes, there will be some level of mismatch-induced loss where the signal (and noise) are so far below the receiver noise figure that the signal will not be heard. In this extremely rare case better antenna matching will help. But we have been saying all along that if the receiver hears an increase in atmospheric noise then there is adequate gain in the system. This is almost always the case.

To the OP: I apologize for helping this discussion veer off into the weeds (or into the noise), but at you have already received some good advice. I'm enjoying the technical debate, and such is thread drift..

[Seeking Solace]

Originally Posted by transmitterdan

Not exactly. A tuner transforms the antenna impedance (S11) at the tuner output terminal to the nominal impedance of the transmitter which is connected to the tuner input. But there is no need to impedance match the receiver since the receiver is already presenting 50 ohms to the antenna. There will be little or no reflected signal at the receiver with or without a tuner since it is internally matched. But because marine transceivers have a tuner it is important to get it tuned right so it isn't acting as a big expensive attenuator sitting between the antenna and the receiver. That is what I am getting at.



They are not the same at all. A non resonant antenna can be a perfectly good receive antenna and yet be a poor transmit antenna. Ask yourself how many receive only receivers you have come across that require resonant antenna tuners? Pretty much none of them do. Television receivers, automobile radio receivers, scanning receivers, etc. do not have resonant tuners. By your reasoning they should not work which is clearly not the case. They work just fine. This is so because whatever power the antenna can collect it delivers to the receiver input terminal. Almost none of that power is reflected back out of the receive port and no resonant tuner is required to make this statement true. All that is required is a halfway decent receiver front end.

I have designed, built and work with some of the largest antennas on earth. I truly do know this subject. For the OP, any several meter long piece of wire plugged into the antenna jack will receive weather faxes and other HF broadcasts just fine. They do not need an antenna tuner.

He's probably done what anybody in their right mind would do and dropped that target HF3 over the side. Let's hope he pulled that wire over to the chainplate and is enjoying it already.

How could it possibly be presenting the receiver with a 50 ohm matched load from an unmatched antenna? It is not damaged because it is not being heated by excessive reflected power that a transmitter would produce with an unbalanced antenna.

How many TV's, scanners, car radios, have resonant antennas? I'd say nearly all of them. Go slap a tape measure on your car radio's antenna I bet you'll find that it closely meets the correct wavelength for it's intended bands. It's not a perfectly resonant antenna, but it doesn't have to be exactly perfect. Same with a TV antenna. Why do you think they have more than just a random wire for TV antennas? If any random length of wire longer than the desired band is enough why bother to make a log periodic yagi for watching television?

I can very much agree that a very poorly matched antenna can be a pretty decent receive antenna. It can not perform nearly as good as a well matched antenna.

Plenty of that power is reflected back. Physics says that it is either going to be absorbed as heat energy or reflected. Remember we're dealing with very small voltages at the receiver. If the mismatch is acting as an attenuator, where is that power going? Attenuators don't just act like a valve to slow an restrict the transfer of power by creating a mismatch. That power is diverted to ground as heat.

I agree he only needs to have an antenna at all to get the weather faxes, or most signals for that matter. How good of an antenna is going to determine how well he can get those signals. I know that in my old two piece transmitter / receivers the tuner was only hooked to the transmitter. I used non resonant receive antennas quite often and it worked brilliantly. I had no idea how much better it was going to be when they put those two items in the same box with a relay. There really is a big difference having that tuner on both sides. Is it needed? Heck no. Will it make weak signal work a dream and allow you to hear stations you otherwise would not? Absolutely.


As to Paul's S/N statement 100% fact. My only comment to that is that I must work those extremely rare cases every day. I often work the weakest signals I come across because it is a challenge and often QRP stations. They're using less than a few hundred milliwatts and small homebrew transmitters. Working those stations is a lot of fun, but sometimes I find out it's not a QRP station at all, but conditions are poor or the other station has some type of antenna issue. This could very much be the case if a sailboat was de-masted and had a very poor antenna.

Thanks for sharing your opinions and expertise from years of working in your perspective fields. I'm curious if he got it working. I hope so.