Short wave antenna and the "Q"

[shortride]

I may be getting in over my head here so bear with me please.

What part does reducing the "Q" in a shortwave antenna play when it comes to improving bandwidth? Does antenna "Q" only applies to TX antennas or does it also apply to an RX wire antenna?

 

[Ed_Seedhouse]

What part does reducing the "Q" in a shortwave antenna play when it comes to improving bandwidth? Does antenna "Q" only applies to TX antennas or does it also apply to an RX wire antenna?

"Q" applies to any resonant circuit. The lower the "Q" the greater the bandwidth but the lower the sensitivity at resonance.

For Shortwave listening you usually want to avoid resonance since any piece of wire longer than about fifteen feet, if properly placed, will almost always give you as much signal as your receiver needs. Of course any antenna has a resonance, so many are purposely cut to put that resonance out of the bands that the user wants to listen on.

An antenna that is resonant at or near a strong signal can overload the front end of a receiver and cause problems over a wide band.

Again for Shortwave you should worry more about putting your receive antenna as high of the ground and as far from sources of RF noise as possible than about it's length or sensitivity.

One exception would be AM band DX where noise is so prevalent that a directional antenna is desirable. A small highly directional antenna, such as a "magnetic" loop, needs to have a sharp resonance to be sensitive enough to be useable.

 

[nanZor]

An antenna that is resonant at or near a strong signal can overload the front end of a receiver and cause problems over a wide band.

Perhaps if you are using it with a portable or something like a Grundig 750. In the case of his high quality Icom R75, not so much of a problem. If overload IS encountered, one uses the RF gain control or attenuator.

Again for Shortwave you should worry more about putting your receive antenna as high of the ground and as far from sources of RF noise as possible than about it's length or sensitivity.

I understand where you are coming from, but this blanket statement may hinder a beginner if they think that length and sensitivity are not important. Power-house SW broadcasting during good propagation conditions - I can see that. If one advances beyond that, or tries to dx weak tropicals, they may want to look into resonant antennas.

The other aspect of this 15 foot universal length solution up is how do you feed it? Attach the center-conductor of 100 feet of RG-174 to the very end of this short wire? - not a good solution unless natural attenuation is what one desires to build. I wish life were just this simple.

I know about modern receivers having enough gain to deal with short antennas, but there is no need to fear resonance with antennas designed to match the feedline impedance. You may not need it, but from what I've read, it almost sounds like 15 feet of wire is all you need for anything, and manufacturers would do well to save consumers money by not even including 9:1 baluns or any other sort of impedance matching components in their antennas.

Putting sensitivity concerns behind, and the wise advice about getting it up high and in the clear, having specific lengths also determines directivity, ie end-fire or broadside, or multiple little lobes. As a newcomer advances, this is something they will want to look into - or at the very least be aware of.

 

[Ed_Seedhouse]

Perhaps if you are using it with a portable or something like a Grundig 750. In the case of his high quality Icom R75, not so much of a problem. If overload IS encountered, one uses the RF gain control or attenuator.

Well, the OP did not say what kind of receiver he is using and I think it's perfectly reasonable to assume that he's most likely to have started out on the lower cost end. Lots of handheld SW receivers are extremely sensitive and with lousy dynamic range.

I understand where you are coming from, but this blanket statement may hinder a beginner if they think that length and sensitivity are not important. Power-house SW broadcasting during good propagation conditions - I can see that. If one advances beyond that, or tries to dx weak tropicals, they may want to look into resonant antennas.

But we have no reason to suppose that the OP has such a radio. And with the more expensive radios for listening, sensitivity will be just as high and there is little need for a resonant antenna above the A.M. broadcast band. At BC or below a resonant antenna will help to counter the insensitivity of the small highly directional magnetic loops that are generally best for good DX work.

The other aspect of this 15 foot universal length solution up is how do you feed it? Attach the center-conductor of 100 feet of RG-174 to the very end of this short wire?

Perfectly practical as long as the connections are mechanically sound and the shield of the Coax is grounded. I happen have 100 feet of 75 ohm coax attached to my antenna and it works just fine. Of course it would be silly to do this if I was also transmitting, but I'm not. At HF the loss in such a piece of coax is under two DB. Not worth worrying about.

I know about modern receivers having enough gain to deal with short antennas, but there is no need to fear resonance with antennas designed to match the feedline impedance.

There is virtually no good reason to match feedline impedance with a highly sensitive modern receiver. For transmission of course it is essential. But this is a forum for receiver antennas, not transmitting antennas. For receivers low noise is as important or more so than pure sensitivity. An antenna that brings more signal to the front end also brings more noise.

You may not need it, but from what I've read, it almost sounds like 15 feet of wire is all you need for anything, and manufacturers would do well to save consumers money by not even including 9:1 baluns or any other sort of impedance matching components in their antennas.

Well the people who make antennas generally don't also make receivers and everyone is driven by profit, of course. So it is in their interest to seduce the buyer into paying as much as they can extract from him.

Putting sensitivity concerns behind, and the wise advice about getting it up high and in the clear, having specific lengths also determines directivity, ie end-fire or broadside, or multiple little lobes. As a newcomer advances, this is something they will want to look into - or at the very least be aware of.

A short antenna also has the advantage of more or less omnidirectional pattern at common shortwave frequencies.

Once you get into the VHF and UHF ranges you should be using a vertically polarized antenna anyway.

 

[Token]

I may be getting in over my head here so bear with me please.

What part does reducing the "Q" in a shortwave antenna play when it comes to improving bandwidth? Does antenna "Q" only applies to TX antennas or does it also apply to an RX wire antenna?

Q applies to any antenna system, TX or RX. It also applies to multiple circuits in your receiver. But, in general, for listening applications you do not need to concern yourself with it. That does NOT mean it is not an important factor, it just means that for a given antenna design the Q remains fairly constant, and is not something you generally “adjust” at will.

If you really want to get into the level of understanding the hows and whys a few short posts on these forums is not going to do it, in fact it likely will result in further confusion because of the abbreviated nature of the answers. A good starting point might be certain publications, possibly starting with the ARRL Antenna Handbook. While it does not go into the details of Q too far it does tie it into bandwidth, and how it affects your selection of antennas for specific applications.

As a general statement the lower the Q the broader the optimal bandwidth, but the lower the sensitivity. A high Q antenna might be very sensitive, but very narrow banded. While “general” SW listening would seem to call for a low Q antenna the truth is you can have a resonant antenna with a reasonable Q, say a dipole with a Q around 12 to 15, that works very well on a specific band and acceptably well across a wider bandwidth. Unless you really have a desire to know don’t get too wrapped up in the theory, many things that look bad in theory work pretty well in the real world.

My primary “general” listening antennas are all antennas cut for specific bands, they just happen to work acceptably well outside those bands also, within limitations. I do have some more targeted antennas for specific bands/regions of the world.

T!

 

[nanZor]

Ed - I had the advantage of knowing he now has an R75 in addition to an R7100 (lucky guy!) from his other threads.

I'm just trying to caution about well-meaning generalities without specifying the other caveats that might leave one thinking that there is a tabloid like conspiracy about using antennas designed for specific purposes.

For instance, I use antennas well UNDER 15 feet due to space limitations - Hi-Q loaded verticals. However, to get them acceptably efficient, I must replace the missing inductive and/or capacitive reactance with either a flat-top / top-hat, or coil and whip combo which typically leaves only 6 to 8 feet of vertical underneath to do all the real work - but tune out of band, and efficiency goes way down. SWL's that want to do this may look into rewinding Hustler 75/80m resonator coil forms for their band of interest, but that's another project thread...

What might be very helpful is knowing that even if one wanted to use just a 15 foot antenna horizontally, is knowing about "what is high"? 10 feet - 20 feet - 75 feet?

A quick rule of thumb would be that any horizontal HF antenna that is not at least a quarter-wave high will exhibit a high angle of vertical radiation/reception depending on frequency, ie:

234 / f mhz = length in feet for a quarter wave.

Lets say that one wanted to use that 15 foot antenna for the 49 meter band, about 6mhz. At 6 mhz, one would ideally want the antenna to be at *least*

234 / 6 = 39 feet high - and that's just the start. Ideally one wants to get it between a quarter and a half-wave, so that means anywhere between 40 feet and 80 feet!

If this antenna is mounted lower than 39 feet, then on the 49 meter band, the major elevation lobe will be very high, and you can count on about 300 mile reception during the day, and of course much more at night, but still be limited due to it being below a quarter wave high.

I'm getting off track, but the point here is that while a 15 foot antenna that is not impedance matched is an ok way to start, don't stop there despite modern receivers having good sensitivity. We both belong to the club that desires a good S/N ratio, rather than just banging the s-meter, but newcomers should know there are other considerations that they will want to keep in mind from the start - it will save them a lot of grief - or at least a lot of copper.

 

[shortride]

Ed - I had the advantage of knowing he now has an R75 in addition to an R7100 (lucky guy!) from his other threads.

I'm just trying to caution about well-meaning generalities without specifying the other caveats that might leave one thinking that there is a tabloid like conspiracy about using antennas designed for specific purposes.

For instance, I use antennas well UNDER 15 feet due to space limitations - Hi-Q loaded verticals. However, to get them acceptably efficient, I must replace the missing inductive and/or capacitive reactance with either a flat-top / top-hat, or coil and whip combo which typically leaves only 6 to 8 feet of vertical underneath to do all the real work - but tune out of band, and efficiency goes way down. SWL's that want to do this may look into rewinding Hustler 75/80m resonator coil forms for their band of interest, but that's another project thread...

What might be very helpful is knowing that even if one wanted to use just a 15 foot antenna horizontally, is knowing about "what is high"? 10 feet - 20 feet - 75 feet?

A quick rule of thumb would be that any horizontal HF antenna that is not at least a quarter-wave high will exhibit a high angle of vertical radiation/reception depending on frequency, ie:

234 / f mhz = length in feet for a quarter wave.

Lets say that one wanted to use that 15 foot antenna for the 49 meter band, about 6mhz. At 6 mhz, one would ideally want the antenna to be at *least*

234 / 6 = 39 feet high - and that's just the start. Ideally one wants to get it between a quarter and a half-wave, so that means anywhere between 40 feet and 80 feet!

If this antenna is mounted lower than 39 feet, then on the 49 meter band, the major elevation lobe will be very high, and you can count on about 300 mile reception during the day, and of course much more at night, but still be limited due to it being below a quarter wave high.

I'm getting off track, but the point here is that while a 15 foot antenna that is not impedance matched is an ok way to start, don't stop there despite modern receivers having good sensitivity. We both belong to the club that desires a good S/N ratio, rather than just banging the s-meter, but newcomers should know there are other considerations that they will want to keep in mind from the start - it will save them a lot of grief - or at least a lot of copper.

More food for thought on antenna "Q". I mainly ask the question to see if I understood the relationship of "Q" and bandwidth. I like to experiment and I can't think of anything else as easy to do.

 

[Ed_Seedhouse]

More food for thought on antenna "Q". I mainly ask the question to see if I understood the relationship of "Q" and bandwidth. I like to experiment and I can't think of anything else as easy to do.

Well, "Q" is a measurement of resonance, and was originally called "Quality Factor". Many electronic (and other) systems are resonant. The higher the "Q" of a resonance the higher the peak gain is and the narrower the bandwidth.

Sometimes you want a system to be resonant, sometimes you don't.

Broadcast band Transmitting antennas are generally designed to be resonant with as high a "Q" as feasible, simply to ensure that the transmitted power is as great as possible. Since they are limited to a specific frequency this is the ideal.

Amateur transmitting antennas need to have a lower "Q" because they need to transmit at many frequencies, but they are still generally resonant to allow maximum transmission of power to the ether.

For receiving antennas resonance is basically irrelevant so long as enough signal is being received. But every antenna does have a resonant frequency.

Audio components on the other hand seek to suppress resonance as much as possible, so they will have the widest bandwidth possible. Some audio components, particularly transducers such as loudspeakers and headphones, are naturally resonant and can never be made un resonant. So the "Q" is kept low to allow for wider bandwidth.

 

[Ed_Seedhouse]

I'm just trying to caution about well-meaning generalities without specifying the other caveats that might leave one thinking that there is a tabloid like conspiracy about using antennas designed for specific purposes.

Of course the question of just what to say and what to leave out is important for any writer attempting to explain something. Explain too little and you might be seen as withholding vital information. Say too much and you risk boring your audience with (to them) extraneous detail.

Everyone who writes will see this problem differently and make different choices as to just what they explain and what they leave out. I do not see this as a matter of "right" or "wrong" and don't find criticism of these choices to be very helpful.

Correction of factual errors, on the other hand, is always welcome and appreciated.

If, on the other hand, you don't like my choices about what to explain and what to leave out, then I invite you to post your own message with what you think is the correct balance. I might even learn something from your better presentation, if I see that it is better.

One thing I will try to avoid is criticize your choice of what to put in and what to leave out unless, I feel it is critical to the question asked, and even then the proper approach is simply to post a factual correction. I will suggest that you might consider the same approach, though of course you are free to write as you wish.

If you want me to change the way I write I will consider doing it upon offer of sufficient remuneration. Otherwise, I'm 69 years old and don't have any plans to change my approach to life, or writing.

 

[Token]

Well, the OP did not say what kind of receiver he is using and I think it's perfectly reasonable to assume that he's most likely to have started out on the lower cost end. Lots of handheld SW receivers are extremely sensitive and with lousy dynamic range.



But we have no reason to suppose that the OP has such a radio. And with the more expensive radios for listening, sensitivity will be just as high and there is little need for a resonant antenna above the A.M. broadcast band. At BC or below a resonant antenna will help to counter the insensitivity of the small highly directional magnetic loops that are generally best for good DX work.

The thread right before this one (Recommendation for an antenna) in this same forum the OP discusses his radio, an Icom R75. Along with that it took less than 45 seconds to click his name on his post, select “Find all post by shortride” and find him asking about the R75 and the R7100. Similarly it took about the same amount of time to do that with regards to you and find out you use or have used a Sat 750, a PCR-1500, and a 40 foot random wire. You may use other things as well, but those are what showed up without taking the time to open any posts. In general, before I respond to anyone whom I am not familiar with, I always try to look at a few past posts, just to see what their experience level is. We all have brain fade moments and can post something sounding very newby’ish accidentally, even if very experienced.

For Shortwave listening you usually want to avoid resonance since any piece of wire longer than about fifteen feet, if properly placed, will almost always give you as much signal as your receiver needs. Of course any antenna has a resonance, so many are purposely cut to put that resonance out of the bands that the user wants to listen on.

The other aspect of this 15 foot universal length solution up is how do you feed it? Attach the center-conductor of 100 feet of RG-174 to the very end of this short wire? - not a good solution unless natural attenuation is what one desires to build. I wish life were just this simple.

Perfectly practical as long as the connections are mechanically sound and the shield of the Coax is grounded. I happen have 100 feet of 75 ohm coax attached to my antenna and it works just fine. Of course it would be silly to do this if I was also transmitting, but I'm not. At HF the loss in such a piece of coax is under two DB. Not worth worrying about.

I know about modern receivers having enough gain to deal with short antennas, but there is no need to fear resonance with antennas designed to match the feedline impedance. You may not need it, but from what I've read, it almost sounds like 15 feet of wire is all you need for anything, and manufacturers would do well to save consumers money by not even including 9:1 baluns or any other sort of impedance matching components in their antennas.

There is virtually no good reason to match feedline impedance with a highly sensitive modern receiver. For transmission of course it is essential. But this is a forum for receiver antennas, not transmitting antennas. For receivers low noise is as important or more so than pure sensitivity. An antenna that brings more signal to the front end also brings more noise.

Possibly if you are listening to power house SW BC stations there is little need for a resonant antenna or an antenna longer than 15 feet. But chasing weak signals, utilities, pirates, and flea power SW BC stations a resonant antenna, or random wires with large capture areas, can make all the difference in the world.

Out of curiosity I just now tried something, admittedly I had never tried an intentionally suboptimal antenna like a 15 foot wire compared to any of my other antennas. Among other antennas I have dipoles or Inverted-V’s here for 160, 80, 60, 40, and 20 meters. There is an extra feedline going up one of my main towers so I attached a 18 foot chunk of wire to it (longer than the 15 foot minimum you describe, no balun, since you say impedance is not important for receive applications), oriented along the same rough bearing as the 40 and 160 meter Inverted-V’s, other antennas are on other bearings. The 18 foot wire is at a height of about 32 feet, the other antennas are probably pretty close to that on average, with some a bit higher and one or two slightly lower. 18 feet of wire should approach resonance at about 13 MHz, and the 32 feet should be plenty high for that freq. For this comparison I did not use any of my directional wire antennas, the Rhombics and wire beams were not compared.

The feedlines for all antennas tested are approximately the same length, roughly 90 to 140 feet, depending on which antenna. The feedline used is RG-214 and LMR-400, depending on which antenna it is. All feedlines are properly grounded and have identical lightning protection. The 18 foot random wire is fed with about 110 feet of RG-214.

For simplicity I am going to call the 18 foot antenna, antenna “S” (for “short&#8221 from now on.

The first test was “S” against the 40 meter Inverted-V. Starting in the V’s wheelhouse at 7240 kHz the noise floor on the V is about –135 dBm (20 kHz sample width on the Excalibur). Going to “S” the noise floor for the same sample width is about –127 dBm. Noise floor advantage, at the V’s resonant frequency, to the V.

Picking freqs at more or less random, noise floor, V vs 20 footer:
3000 kHz, -145 dBm for the 40V, -132 dBm for “S”
5000 kHz, -141 dBm for the 40V, -137 dBm for “S”
9000 kHz, -137 dBm for the 40V, -123 dBm for “S”
13000 kHz, -146 dBm for the 40V, -134 dBm for “S”
17000 kHz, -146 dBm for the 40V, -137 dBm for “S”
20000 kHz, -145 dBm for the 40V, -138 dBm for “S”
24000 kHz, -143 dBm for the 40V, -140 dBm for “S”
28000 kHz, -145 dBm for the 40V, -143 dBm for “S”

Every freq, from 3000 to 28000 kHz tested, including the resonant freqs of both antennas, show the Inverted V has a lower noise floor. I am thinking maybe the lack of a balun on “S” is hurting us here.

Next would be sample signals, selected at random, to show signal to noise ratios. I intentionally did not pick any signals that one antenna could receive and the other could not see at all. For this purpose the SNR is defined as the peak signal level above the average noise floor on a 20 kHz span sample. Noise floor is averaged over 2 seconds and peak signal level is defined as the peak signal in a 15 second period of time.

2500 kHz WWV, 16 dB SNR on 40V, 14 dB SNR for “S”
5000 kHz WWV, 47 dB SNR on 40V, 45 dB SNR for “S”
10000 kHz WWV, 72 dB SNR on 40V, 63 dB SNR for “S”
15000 kHz WWV, 62 dB SNR on 40V, 67 dB SNR for “S”
20000 kHz WWV, 26 dB SNR on 40V, 30 dB SNR for “S”

4555 kHz CODAR, unk loc, 45 dB SNR on 40 V, 28 dB SNR on “S”
6360 kHz GW-Tor sig, 38 dB SNR on 40V, 28 dB SNR on “S”
8694 kHz Unk FSK, 850 Hz shift, 70 dB SNR on 40V, 64 dB on “S”
10430 kHz Unk FSK, 850 Hz shift, 65 dB SNR on 40V, 37 dB on “S”
12828.5 kHz Unk STANAG 4285, 30 dB SNR on 40V, 35 dB SNR on “S”
15610 kHz WEWN BC stn, 55 dB SNR on 40V, 60 dB SNR on “S”
20500 kHz Unk OTHR, 32 dB SNR on 40V, 23 dB SNR on “S”

The take away form this is that antenna “S” could not compete with the 40 meter inverted V through most of the HF range. Near frequencies that it was resonant on and the 40 meter was not “S” did better, but only slightly. I suspect if it was a dipole and had a balun it would do better yet near those resonant freqs.

How about a bigger antenna, lets say the 160 meter inverted V? OK, it is not truly an inverted V because the included angle is not quite small enough, call it a dropping dipole. This antenna is mounted with the feed point at about 40 feet, very much less than optimal for 160 meters. To make things a little better for antenna “S” the 160 antenna does NOT have a 1:1 balun, it is simply a dipole fed by direct connection to the RG-214 center conductor and outer shield. The 160 meter antenna is cut for 1925 kHz.

Noise floor:
890 kHz, -132 dBm for 160V, -145 dBm for “S”
1925 kHz, -127 dBm for 160V, -145 dBm for “S”
3000 kHz, -123 dBm for the 160V, -132 dBm for “S”
5000 kHz, -137 dBm for the 160V, -137 dBm for “S”
9000 kHz, -137 dBm for the 160V, -123 dBm for “S”
13000 kHz, -140 dBm for the 160V, -134 dBm for “S”
17000 kHz, -142 dBm for the 160V, -137 dBm for “S”
20000 kHz, -133 dBm for the 160V, -138 dBm for “S”
24000 kHz, -132 dBm for the 160V, -140 dBm for “S”
28000 kHz, -145 dBm for the 160V, -143 dBm for “S”

A bit more of a mixed bag here, antenna “S” competing much better now, with lower noise floor than the 160V on several frequencies, a huge difference down on the freq 160V is resonant on. The much, much bigger antenna (about 243 feet of wire), with a much greater capture area is bringing in a lot more noise. But, does it also bring in bigger signals to compensate for that bigger noise?

2500 kHz WWV, 26 dB SNR on 160V, 20 dB SNR for “S”
5000 kHz WWV, 40 dB SNR on 160V, 43 dB SNR for “S”
10000 kHz WWV, 65 dB SNR on 160V, 60 dB SNR for “S”
15000 kHz WWV, 60 dB SNR on 160V, 75 dB SNR for “S”
20000 kHz WWV, 33 dB SNR on 160V, 30 dB SNR for “S”

550 kHz MW BC, 70 dB SNR on 160V, 55 dB SNR for “S”
850 kHz MW BC, 40 dB SNR on 160V, 20 dB SNR for “S”
1650 kHz MW BC, 45 dB SNR for 160V, 20 dB SNR for “S”
4555 kHz CODAR, unk loc, 40 dB SNR on 160 V, 22 dB SNR on “S”
6360 kHz GW-Tor sig, 47 dB SNR on 160V, 36 dB SNR on “S”
8694 kHz Unk FSK, 850 Hz shift, 65 dB SNR on 160V, 55 dB on “S”
10430 kHz Unk FSK, 850 Hz shift, 47 dB SNR on 160V, 30 dB on “S”
12828.5 kHz Unk STANAG 4285, 23 dB SNR on 160V, 27 dB SNR on “S”
15610 kHz WEWN BC stn, 70 dB SNR on 160V, 65 dB SNR on “S”
29850 kHz SKiYMET meteor radar, 30 dB SNR on 160V, 20 dB SNR on “S”

On all of these signals the 160V produced a higher SNR than antenna “S”, with the exception of near “S” resonance and on the 5000 kHz WWV. So yes, the noise floor was up on the bigger antenna, but so were the signals levels.

Yeah, a random hunk of wire just connected to the coax / feedline will work, no doubt. And if you get it up high and away from noise it will be pretty decent. I have a feeling many of us start out that way. But a good, resonant, antenna will work better, even for receive only applications.

Personally, I have not made do with one antenna in decades. Typically I use several antennas, some resonant at low freqs, some at mid freqs, some at higher freqs, and select among those as needed. Unless a person is space limited there is no good reason not to have multiple antennas, on multiple bearings, and optimized for different parts of the spectrum.

A short antenna also has the advantage of more or less omnidirectional pattern at common shortwave frequencies.

This is also a disadvantage. A couple of slightly directional antennas on different bearings can help deal with noise sources and also when there are multiple stations on freq or near the same freq.

T!

 

[LtDoc]

Token,
At least you got the polarity thingy out of the way, that would make more difference than anything else would considering the two antennas in comparison testing.
Forget the balun thingy, it would have no difference for SNR comparisons, or at least nothing of consequence. The 'length's of the two antennas, and particularly what was used as that 'shorty's 'other-half' would make a much greater difference with SNR.
Even so, your testing shows that there is definitely a difference, but I don't think I'd call it a huge one except for certain frequencies, which is also normal.
- 'Doc

 

[Ed_Seedhouse]

The thread right before this one (Recommendation for an antenna) in this same forum the OP discusses his radio, an Icom R75. Along with that it took less than 45 seconds to click his name on his post, select “Find all post by shortride” and find him asking about the R75 and the R7100.

I am sorry, but I am just not going to search every thread anyone has posted. He asked a question in this thread, and I answered it.

This is also a disadvantage. A couple of slightly directional antennas on different bearings can help deal with noise sources and also when there are multiple stations on freq or near the same freq.

Well that's true, but hardly relevant for someone who is just into the hobby and isn't sure what "Q" is yet.

 

[Ed_Seedhouse]

Possibly if you are listening to power house SW BC stations there is little need for a resonant antenna or an antenna longer than 15 feet. But chasing weak signals, utilities, pirates, and flea power SW BC stations a resonant antenna, or random wires with large capture areas, can make all the difference in the world.

I normally listen to SSB on various ham bands on my dinky little un-tuned antenna, and I've heard them from as far away as Indonesia on less than a hundred watts. So methinks you may possibly be exaggerating just a bit.

Sure, if you are listening for the most extreme DX a resonant and directional antenna can make all the difference. I see (and saw) no evidence on this thread that the OP is yet involved in the hobby to that extent.

Maybe eventually he will have a farm of Beverage antennas with a bunch of Yagis up on 100 foot towers. I wouldn't know. Until then I do know he can have big fun with a fairly dinky wire well up in the air and away from local RF noise. Such a wire would clearly be better than what I can put up in my tiny back yard but that hasn't stopped me from having a lot of fun, either.

 

[Token]

Possibly if you are listening to power house SW BC stations there is little need for a resonant antenna or an antenna longer than 15 feet. But chasing weak signals, utilities, pirates, and flea power SW BC stations a resonant antenna, or random wires with large capture areas, can make all the difference in the world.

I normally listen to SSB on various ham bands on my dinky little un-tuned antenna, and I've heard them from as far away as Indonesia on less than a hundred watts. So methinks you may possibly be exaggerating just a bit.

Sure, if you are listening for the most extreme DX a resonant and directional antenna can make all the difference. I see (and saw) no evidence on this thread that the OP is yet involved in the hobby to that extent.

I was not exaggerating at all. I said resonant antennas and antennas with large capture areas can make all the difference in the World. I did not say small antennas don’t work at all, but I will say, without reservation, that small random antennas do not work as well as full sized resonant antennas for the frequency of interest. When the small random antenna runs into its performance limitation the larger capture area antennas or resonant antennas of similar physical size continue to work. Of course, eventually you run into the limitations of each and every antenna, with a good antenna the limitations just come later.

As for hearing Indonesian stations with less than 100 Watts on your wire…what, exactly does that prove? I have worked that region, not just “heard” them, with less than 100 Watts…and that also proves exactly nothing. I have also literally loaded a set of bed springs and worked Australia…again proving nothing, and I would not recommend it for someone’s only setup even though it worked for a 2 way QSO of over 8500 miles. When conditions are right almost anything is possible. And when conditions are wrong the biggest, baddest antenna in the World does no good. But, the better the entire system, from antenna to earphones, the more often conditions are “right”.

I have to say, I don’t think I have ever heard anyone say “I wish I had a worse antenna because these DX stations are just too easy to receive”, while I know very well that I have often heard people wish for better antennas.

For Shortwave listening you usually want to avoid resonance since any piece of wire longer than about fifteen feet, if properly placed, will almost always give you as much signal as your receiver needs.

<<<snip>>>

An antenna that is resonant at or near a strong signal can overload the front end of a receiver and cause problems over a wide band.

Your claim that I was responding to was that resonant antennas are not needed, indeed not desired, “you usually want to avoid resonance”, in your words. My claim is that resonant antennas are almost always desirable, just not always possible for the bandwidth we are talking about, so you should set up as best you can. In the case of having too much signal you can always decouple to prevent overload, but if you don’t have enough signal there is little you can do to resolve the situation.

And a non-resonant antenna can also overload a front end, there is nothing “magical” about an untuned antenna not overloading a radio. What does happen is that the untuned antenna might, indeed often will, receive the desired signal at a lower level, possibly reducing the probability of overload for radios with poor dynamic range or the inability to attenuate strong signals. Unfortunately it will also reduce the level of signals that are not too strong (can’t have it both ways, it will not reduce only the “too strong” signals), sometimes causing those signals to be lost below your detection threshold. As the numbers I posted earlier show, an untuned antenna does not always lower the noise floor over a tuned antenna. And dropping the peak signals without dropping the noise floor means you have just reduced signal to noise, never a good thing to have as a goal.

Your contention that “any piece of wire longer than about fifteen feet, if properly placed, will almost always give you as much signal as your receiver needs” is misleading as guidance to new users. In marginal conditions you are going to be left wanting…if you even realize at all that you are not hearing things you should be. If 15 feet of wire is all that is required why do people every put up more? This advice very possibly could misguide the new SWL to think “why put up more than 15 feet, if that is all I need”?

If someone only has the room for 15 feet of wire then yes indeed, they should put that up, and it will work, possibly even better than they hoped. But, if they can put up 30 feet, or 50 feet, or even 75 feet, they will probably be better off, it will certainly perk up those seemingly “dead” lower freqs that the 15 foot wire would be killing. There is a difference between “works” and “works well”.

T!

 

[Token]

Even so, your testing shows that there is definitely a difference, but I don't think I'd call it a huge one except for certain frequencies, which is also normal.

The fact that at most frequencies (with only a few exceptions) the larger antenna did better (better SNR), even when not at a resonant frequency was, I thought, significant. To tell the truth I did not expect those deltas when getting very far off the tuned band, particularly at the higher end of the spectrum.

In general I agree, the difference is not huge&#8230;unless you need that extra 6 dB (or whatever it might be on that specific signal) to bring the signal from unusable to copyable. On moderate to armchair copy signals it will not matter in the least, but when having to dig for them it will be exceptionally important.

T!

 

[nanZor]

Shortride - hope you haven't run away screaming.

Believe it or not, this a friendly, yet passionate discussion over something we love. The best thing you can do is go ahead and try the 15 foot antenna for a week or month or however long you like. But as a newcomer to the hobby I recommend you not stop here, and try out other antenna combinations as well and put some of your own experience under your feet.

Ed - I appreciate your clear and precise writing - I just disagree with what appears to be general sweeping statements that may not fit under all circumstances and felt compelled to respond. I have a feeling we'll just have to agree to disagree based upon our individual experience. I'll buy you a beer just the same!