Re: Topband: 8 circle: DXE vs Hi-Z
Bravo, John! Well stated on all points. No disparaging comments noted. I especially appreciate your discussion of RDF and what it actually means in practice. As you commented, in practice, RDF is calculated (EZNEC, etc.) assuming equal amplitude distribution of noise over all 3D free space. On 160m, in North Florida, I am sure that the assumed equal distribution of noise is never the real case. It is actually possible to calculate RDF for any arbitrary spatial distribution of noise, but to do so you must mathematically characterize the noise distribution in 3D - obviously a formidable task at 1.8 MHz. Usually everyone just takes the simplifying leap and assumes that all the bad noise is coming from off the back and the sides of the antenna, in some well-behaved average way. Noise sourced from the front of the antenna pattern is largely ignored. Antenna patterns are often optimized? to reduced side lobes to near zero levels. The main lobe is generally broadened as a result of such side lobe optimizations. Now consider the case of non-uniform noise distribution, with a high noise level broadly sourced at the front of the antenna pattern and lower noise levels sourced on the sides and back of the antenna pattern. By minimizing noise reception in the side lobes, the main lobe is now broadened and thus is exposed to a greater solid angle of high noise source. Furthermore, the increased exposure to high noise takes place in the main lobe, which has the highest pattern field gain. The actual antenna RDF would be substantially degraded as a result of additional received noise power. For this example, optimizing the antenna pattern for minimum side lobes would actually degrade the antenna's environmental SNR. RDF is a very useful metric for comparing receiving antennas. But, we must use the concept in its entirety - we cannot ignore the system aspects that are hard to measure, calculate, or characterize. Perhaps W7EL will incorporate an arbitrary 3D noise model in his next EZNEC update? 73, Terry K4RX John wrote in part: ...RDF as a receiving metric: RDF is indeed a very useful metric for comparing receiving antennas. However, we need to be aware that it assumes the ambient background (atmospheric) noise is uniformly distributed in 3-dimensional space, which is not always true in specific instances. For this reason, RDF may not exactly predict the differences between two arrays in any given situation. It is possible for a system with a lower RDF to equal or even outperform another system with higher RDF under certain noise conditions. If the noise were always uniformly distributed, then RDF would perfectly predict relative receiving performance (actually SNR). The next point about RDF is that it is calculated for a specific signal arrival direction in three dimensional space. In terms of azimuth, it is the peak direction of the forward lobe. In elevation, it is common practice to use 20 degrees, which can be considered appropriate for DX reception. If the signal arrives from a different azimuth or elevation angle, the SNR advantage predicted by RDF may not actually be realized. I have seen a simple low dipole with a lousy RDF occasionally outperform my 8-circle system by a large amount when the elevation angle of arriving signals is very high and the RDF advantage of the array cannot be realized. As RDF gets higher, the beamwidth of the antenna system generally gets narrower. You can see this if you look at chart #2 in K7TJR's Dayton presentation (http://www.kkn.net/dayton2014/HiZ_DAYTON_2014_7n2.pdf). This brings up another point. By making the RDF very high, you are necessarily restricting the angular sector over which the antenna delivers its best performance. This is fine as long as the angular sector coincides with a direction that is important to you. The flip side is you give up some of that performance outside that sector. For switched arrays with a finite number of selectable directions, that could be a disadvantage when a direction of interest falls halfway between contiguous switching directions. Looking at the pattern of the array will tell you what you give up in the in between directions. These comments with respect to RDF are not intended to be disparaging. On the contrary I do believe RDF is an excellent tool for comparing receiving antennas. You just have to aware of what it actually means in practice... 73, John W1FV _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: 8 circle: DXE vs Hi-Z
Excellent discussion John and Terry. Interestingly enough if you take the 8 elements in a 200 foot circle you can optimize the peak RDF to nearly 15dB. M.T. Ma in his book outlines his math to optimize feeds for the specific purpose of maximizing directivity. Using his mathematics produces 15 dB of peak RDF in this circle with horrible side lobes and a narrow beam. If you set the 8 elements for crossfire phasing you can get an RDF of 14 dB or so. However using either of these phasing and amplitude schemes requires a circuitry system accuracy that is presently unobtainable for backyard installations. Relaxing the RDF to 13.45 and playing with the phasings allows an array to be realized using the technology at hand. Lowering the available RDF of these 8 elements to 13.45 causes the close in side lobes to decrease and the 90 degree side lobes to increase. Interestingly enough these 90 degree side lobes are at a very low elevation angle. Further lowering of the RDF allows a very clean pattern as John and Terry have pointed out. At my location the side lobes generated by keeping the RDF at 13.45 cause none or little harm to the real SNR at my location Just as Terry has pointed out. My goal for designing the all active 8 element array was the very same as Joel has mentioned and that was to build the best performing array that I could for myself in my environment. After all the tests I have made at this location comparing receiving antennas, I wait with great anticipation the tests Joel is making. It will be most interesting to me if one can tell the difference between systems with an RDF within a dB or so on very weak signals. I have successfully measured 1 dB difference in S+N to N ratios between antennas using Spectran. There are things to be learned here. Lee K7TJR -Original Message- From: Topband [mailto:topband-boun...@contesting.com] On Behalf Of Terry Posey Sent: Wednesday, December 17, 2014 7:57 AM To: 'John Kaufmann'; topband@contesting.com Subject: Re: Topband: 8 circle: DXE vs Hi-Z Bravo, John! Well stated on all points. No disparaging comments noted. I especially appreciate your discussion of RDF and what it actually means in practice. As you commented, in practice, RDF is calculated (EZNEC, etc.) assuming equal amplitude distribution of noise over all 3D free space. On 160m, in North Florida, I am sure that the assumed equal distribution of noise is never the real case. It is actually possible to calculate RDF for any arbitrary spatial distribution of noise, but to do so you must mathematically characterize the noise distribution in 3D - obviously a formidable task at 1.8 MHz. Usually everyone just takes the simplifying leap and assumes that all the bad noise is coming from off the back and the sides of the antenna, in some well-behaved average way. Noise sourced from the front of the antenna pattern is largely ignored. Antenna patterns are often optimized? to reduced side lobes to near zero levels. The main lobe is generally broadened as a result of such side lobe optimizations. Now consider the case of non-uniform noise distribution, with a high noise level broadly sourced at the front of the antenna pattern and lower noise levels sourced on the sides and back of the antenna pattern. By minimizing noise reception in the side lobes, the main lobe is now broadened and thus is exposed to a greater solid angle of high noise source. Furthermore, the increased exposure to high noise takes place in the main lobe, which has the highest pattern field gain. The actual antenna RDF would be substantially degraded as a result of additional received noise power. For this example, optimizing the antenna pattern for minimum side lobes would actually degrade the antenna's environmental SNR. RDF is a very useful metric for comparing receiving antennas. But, we must use the concept in its entirety - we cannot ignore the system aspects that are hard to measure, calculate, or characterize. Perhaps W7EL will incorporate an arbitrary 3D noise model in his next EZNEC update? 73, Terry K4RX John wrote in part: ...RDF as a receiving metric: RDF is indeed a very useful metric for comparing receiving antennas. However, we need to be aware that it assumes the ambient background (atmospheric) noise is uniformly distributed in 3-dimensional space, which is not always true in specific instances. For this reason, RDF may not exactly predict the differences between two arrays in any given situation. It is possible for a system with a lower RDF to equal or even outperform another system with higher RDF under certain noise conditions. If the noise were always uniformly distributed, then RDF would perfectly predict relative receiving performance (actually SNR). The next point about RDF is that it is calculated for a specific signal arrival direction in three dimensional space. In terms of azimuth, it is the peak direction of the forward lobe. In elevation, it is common
Re: Topband: 8 circle: DXE vs Hi-Z
All this discussion about RDF overlooks the issue of polarization. If you make an array of verticals with a certain RDF (assuming noise comes from all directions uniformly), the array will be better than an individual vertical by the RDF factor. However, what I have found is that a horizontally polarized antenna, such as a low dipole frequently receives considerably better than a vertical. In that case, you would be better off using an array of low dipoles. The reason why horizontal polarization can be better is that the horizontal component of terrestrial based noise is highly attenuated over distance as a ground wave. Rick N6RK _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: 8 circle: DXE vs Hi-Z
Good points about polarization. If the signals and/or noise are polarized predominantly in one state, then RDF may not be a good predictor of SNR performance, particularly if the antenna receives predominantly in an orthogonal polarization. On the other hand, if the polarization state of the signals and noise evolve randomly with no preference for any one state, which is often assumed for skywave signals, then RDF will be--on average--a good receiving metric, subject to the previous stated qualifications about the spatial distribution of the received noise. However, some of the past discussions on this reflector about preferential polarization of skywave signals on 160 may call into question the assumption of randomly polarized signals. 73, John W1FV -Original Message- From: Topband [mailto:topband-boun...@contesting.com] On Behalf Of Richard (Rick) Karlquist Sent: Wednesday, December 17, 2014 3:19 PM To: Lee K7TJR; 'Terry Posey'; 'John Kaufmann'; topband@contesting.com Subject: Re: Topband: 8 circle: DXE vs Hi-Z All this discussion about RDF overlooks the issue of polarization. If you make an array of verticals with a certain RDF (assuming noise comes from all directions uniformly), the array will be better than an individual vertical by the RDF factor. However, what I have found is that a horizontally polarized antenna, such as a low dipole frequently receives considerably better than a vertical. In that case, you would be better off using an array of low dipoles. The reason why horizontal polarization can be better is that the horizontal component of terrestrial based noise is highly attenuated over distance as a ground wave. Rick N6RK _ Topband Reflector Archives - http://www.contesting.com/_topband _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: 8 circle: DXE vs Hi-Z
Hi guys Polarization does play a lot on 160m for two reasons. I can say that because I am using my HWF (two horizontal flags end fire) since 2009. The first one is local man made noise that propagate only vertical due the attenuation on the horizontal component near the ground. And Second the DX signal always come in both polarization. The result form the two reasons is an optimized signal to noise ration using horizontal polarization. I have both WF with the same RDF, during SR or SS there is almost no sky noise coming from the back because of the darkness, however local man made noise comes from any direction, especially if you live in a city lot like I do. Most of the time the noise is coming at the same direction you want to hear the DX, and if you add power line noise the situation deteriorates a lot for the VWF due vertical polarization. Using my HWF I normally get 10 dB better SNR than my VWF that has the same RDF and same aperture of 74 degree measures, I can turn the antenna and measure it, they are not optimized for best F/B, I optimized them for maximum rejection of local man made noise. The HWF is not a dipole. The two phased loops take of angle us 40 degree and there is a huge attenuation for signals above 60 degree. Low dipole is a huge issue if the dipole is resonant, it will interact with all other receiver antennas and will destroy directivity of all of them, if you want to use a low dipole make it not resonant. Gain in not important so it can be short as a 30 m dipole and still will hear the same way. Another issue with low dipoles is the amount of energy absorbed from the TX antenna. If you connect a power meter and a 50 ohms load o the low dipole and transmit KW on the TX antenna, you can measure several WATTS at the low dipole . You can burn you front end with a low resonant dipole. Adding to all that there is another very interesting observation from my last 5 year using a high RDF horizontal RX antenna, when the TX signal refract on the ionosphere the signal split in two waves, that was very well explained by K9LA. What I observed is that these two waves does propagate in different directions. I normally receive VK6 near my SR with better SNR horizontal from 210 degree SSW and with better SNR from 280 degree vertical. Sometimes the horizontal peak is 20 minutes before the vertical peak that is most of the time at my SR. 73's N4IS JC -Original Message- From: Topband [mailto:topband-boun...@contesting.com] On Behalf Of John Kaufmann Sent: Wednesday, December 17, 2014 8:59 PM To: topband@contesting.com Subject: Re: Topband: 8 circle: DXE vs Hi-Z Good points about polarization. If the signals and/or noise are polarized predominantly in one state, then RDF may not be a good predictor of SNR performance, particularly if the antenna receives predominantly in an orthogonal polarization. On the other hand, if the polarization state of the signals and noise evolve randomly with no preference for any one state, which is often assumed for skywave signals, then RDF will be--on average--a good receiving metric, subject to the previous stated qualifications about the spatial distribution of the received noise. However, some of the past discussions on this reflector about preferential polarization of skywave signals on 160 may call into question the assumption of randomly polarized signals. 73, John W1FV -Original Message- From: Topband [mailto:topband-boun...@contesting.com] On Behalf Of Richard (Rick) Karlquist Sent: Wednesday, December 17, 2014 3:19 PM To: Lee K7TJR; 'Terry Posey'; 'John Kaufmann'; topband@contesting.com Subject: Re: Topband: 8 circle: DXE vs Hi-Z All this discussion about RDF overlooks the issue of polarization. If you make an array of verticals with a certain RDF (assuming noise comes from all directions uniformly), the array will be better than an individual vertical by the RDF factor. However, what I have found is that a horizontally polarized antenna, such as a low dipole frequently receives considerably better than a vertical. In that case, you would be better off using an array of low dipoles. The reason why horizontal polarization can be better is that the horizontal component of terrestrial based noise is highly attenuated over distance as a ground wave. Rick N6RK _ Topband Reflector Archives - http://www.contesting.com/_topband _ Topband Reflector Archives - http://www.contesting.com/_topband _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: 8 circle: DXE vs Hi-Z
I forgot to mention another very important development. My friend N8PR is experiencing with the WF in another level, Peter is using a rotator to turn the WF vertical to horizontal. He worked FT4TA on 160m with the WF at 45 degree polarization, (not elevation, the rotor turns axial) and only 45 degree at the right side, turning the WF 45 degree on the left side the signal was below noise and any other polarization was not good that day. Peter has a lot of noise from a AM BC station 1 mile from his QTH and he is working to improve the common node noise. However the experiment with polarization rotation is providing return in new countries for him. Regards JC N4IS -Original Message- From: JC [mailto:n...@comcast.net] Sent: Tuesday, December 16, 2014 1:02 PM To: 'Tom W8JI'; 'Lee K7TJR'; 'Bob Tabke'; 'topband@contesting.com' Subject: RE: Topband: 8 circle: DXE vs Hi-Z Hi guys I would like to commented on the subject of RX comparison Tom when you introduced the RDF methodology to measure directivity, you really hit the nail in the head. I'm working on RX antennas only since 2005, after hundreds of tests, I am sure that just 1db RDF matters a lot. When you compare RX antennas you really want to know how much you can improve from your TX antenna Signal to Noise Ratio. Better RDF means better SNR, similar RX antennas performance have similar RDF. 1 RDF does help a lot when the signal is just 2 db above noise and you can't pull it out, adding just 1 db you can change from 339 to 449 and log a QSO, or new country. 3db SNR is just what you need on cw. The implementation of the RX is different from EZNEC , you need to consider all elements neat resonance that will be part of the RX system and deteriorate RDF, it means deteriorating SNR. Common mode noise is not well understood for most of DXer's including grounding, these are factors to consider as well. My recommendation is to kook in the space you have and select the best RDF Rx antenna for your available space. Nothing beats the 13.8db RDF from 8 circle array, but you need 300ft radius to achieve that directivity. If you are able to broadside some good RX antennas and get over 14 dB RDF you shall expect better SNR than the 8 cycle/300ft. Remember to detune your TX antenna during RX, It is hard to measure that and sometimes the only way is to compare the SNR from the TX antenna with the RX antenna, is you are using a 11db RDF system you should see more than 10db SNR over the TX antenna. It means you can hear Q5 signals not even detected by the TX antenna, it is not about move comfortable e copy , it is about to hear what is not there in the RX antenna. Detuning he tower won't fix other common mode noise, like cables not grounded, bad grounding, rotor cable 120 ft long working like a vertical, etc, It is necessary detune them all. Regards JC -Original Message- From: Topband [mailto:topband-boun...@contesting.com] On Behalf Of Tom W8JI Sent: Tuesday, December 16, 2014 7:52 AM To: Lee K7TJR; 'Bob Tabke'; topband@contesting.com Subject: Re: Topband: 8 circle: DXE vs Hi-Z Lee, We probably will just have to disagree about this. From my viewpoint, the behavior isn't too much different than a big yagi stack or other antennas we are used to. The size of the array generally sets the directivity limits. We can add more elements that are closer-in than optimum, and that can certainly help if the size is smaller than optimum, but the trade is gain or pattern cleanliness and sharpness for size. The forward two elements and back two elements are too close to contribute broadside pattern, which is what provides the clean pattern absent major side lobes in the full size 8 circle. As a matter of fact, adding them in destroys some of the broadside directivity. If, however, we make the array so small that it loses broadside pattern multiplication, then we can see an increase in directivity through the small endfire length increase. A .327wl radius array gives about .25 wl endfire spacing in the primary cells (the center elements), and is not improved in pattern quality by adding the forward and rearward cells. The two forward pairs and rearward pairs are not only too close to have broadside pattern contribution, they are closer endfire. They are about 75% of the endfire spacing in the central quad, and nearly 40% of the broadside width. They certainly can contribute endfire, but they actually remove broadside directivity in the process! In an optimum size array the amplitude ratio from the primary quad has to be 4:1 or 5:1 or more to prevent some pretty significant pattern null area deterioration when the additional 4 elements are added, because they deteriorate broadside pattern multiplication faster than they contribute endfire gain (at ~.187 spacing when the primary endfire cell has .25 wl spacing). If the array is made so small that there is little broadside contribution from array width, then the addition of the four will improve
Re: Topband: 8 circle: DXE vs Hi-Z
Well I disagree that gain isn't important. Maybe you topbanders in the better areas of propagation can afford to throw away many db to get a better rdf, but that sure isn't the case up here in mid-northern VE6 land. I have numerous receive antennas including many beverages and Wellbrook loops (large area) and the Hi-Z 4-8PRO 8 element circle. They all work more or less as expected on the easy stuff and show reasonable directivity but when I need help for the weaker dx, there just isn't any signal there to work with. The beverages do the best of the bunch, they aren't anything special - typically in the 700-1100 foot range. With the many vertical structures I have there is no doubt their patterns are somewhat affected but they seem to work fine for Eu and JA bcb dx vs the loops and the 8 verticals. Not that this has been a good year for much of anything on the low bands in this area. The HI-Z was erected quite aways from anything else which involved bushwhacking and clearing the entire circle, trenching almost 1200 feet of feedline etc so there was a lot of sweat work done on that project. But on 160 and 80 where I have the tx antennas to use as a comparison, the specialized rx stuff just doesn't hear the weaker stuff. And it's not that I have a pristine can hear a pin drop low noise qth, esp on 160 - plenty of flare stack ingitors plus the usual powerline and smps junk. It's especially frustrating to hear all the glowing success stories of these rx arrays and how they make the dx just jump out of the noise and into your log... 73 Don VE6JY On Thu, Dec 18, 2014 at 4:11 AM, JC n...@comcast.net wrote: Hi guys Polarization does play a lot on 160m for two reasons. I can say that because I am using my HWF (two horizontal flags end fire) since 2009. The first one is local man made noise that propagate only vertical due the attenuation on the horizontal component near the ground. And Second the DX signal always come in both polarization. The result form the two reasons is an optimized signal to noise ration using horizontal polarization. I have both WF with the same RDF, during SR or SS there is almost no sky noise coming from the back because of the darkness, however local man made noise comes from any direction, especially if you live in a city lot like I do. Most of the time the noise is coming at the same direction you want to hear the DX, and if you add power line noise the situation deteriorates a lot for the VWF due vertical polarization. Using my HWF I normally get 10 dB better SNR than my VWF that has the same RDF and same aperture of 74 degree measures, I can turn the antenna and measure it, they are not optimized for best F/B, I optimized them for maximum rejection of local man made noise. The HWF is not a dipole. The two phased loops take of angle us 40 degree and there is a huge attenuation for signals above 60 degree. Low dipole is a huge issue if the dipole is resonant, it will interact with all other receiver antennas and will destroy directivity of all of them, if you want to use a low dipole make it not resonant. Gain in not important so it can be short as a 30 m dipole and still will hear the same way. Another issue with low dipoles is the amount of energy absorbed from the TX antenna. If you connect a power meter and a 50 ohms load o the low dipole and transmit KW on the TX antenna, you can measure several WATTS at the low dipole . You can burn you front end with a low resonant dipole. Adding to all that there is another very interesting observation from my last 5 year using a high RDF horizontal RX antenna, when the TX signal refract on the ionosphere the signal split in two waves, that was very well explained by K9LA. What I observed is that these two waves does propagate in different directions. I normally receive VK6 near my SR with better SNR horizontal from 210 degree SSW and with better SNR from 280 degree vertical. Sometimes the horizontal peak is 20 minutes before the vertical peak that is most of the time at my SR. 73's N4IS JC -Original Message- From: Topband [mailto:topband-boun...@contesting.com] On Behalf Of John Kaufmann Sent: Wednesday, December 17, 2014 8:59 PM To: topband@contesting.com Subject: Re: Topband: 8 circle: DXE vs Hi-Z Good points about polarization. If the signals and/or noise are polarized predominantly in one state, then RDF may not be a good predictor of SNR performance, particularly if the antenna receives predominantly in an orthogonal polarization. On the other hand, if the polarization state of the signals and noise evolve randomly with no preference for any one state, which is often assumed for skywave signals, then RDF will be--on average--a good receiving metric, subject to the previous stated qualifications about the spatial distribution of the received noise. However, some of the past discussions on this reflector about preferential polarization of
Re: Topband: 8 circle: DXE vs Hi-Z
My experience is similar to Don's outlined below. Both gain and noise figure are important in very low noise environments. In my own case, I have a noise floor from my TX array in the high -120s or -130s assuming a quiet atmosphere. A high RDF performance RX array often brings virtually no improvement. In my case, since the RX arrays lack gain, they often don't have the horsepower (gain) to reach down and hear the super low level signals picked up by the TX array. Switching from the TX antenna to the high RDF receive array not only fails to make the signal jump out of the noise (what noise?) but fails to hear the signal at all. In these circumstance both gain and noise figure become very important factors. 73. . .Dave, W0FLS - Original Message - From: Don Moman VE6JY ve6j...@gmail.com To: Topband@Contesting. Com topband@contesting.com Sent: Wednesday, December 17, 2014 10:53 PM Subject: Re: Topband: 8 circle: DXE vs Hi-Z Well I disagree that gain isn't important. Maybe you topbanders in the better areas of propagation can afford to throw away many db to get a better rdf, but that sure isn't the case up here in mid-northern VE6 land. I have numerous receive antennas including many beverages and Wellbrook loops (large area) and the Hi-Z 4-8PRO 8 element circle. They all work more or less as expected on the easy stuff and show reasonable directivity but when I need help for the weaker dx, there just isn't any signal there to work with. The beverages do the best of the bunch, they aren't anything special - typically in the 700-1100 foot range. With the many vertical structures I have there is no doubt their patterns are somewhat affected but they seem to work fine for Eu and JA bcb dx vs the loops and the 8 verticals. Not that this has been a good year for much of anything on the low bands in this area. The HI-Z was erected quite aways from anything else which involved bushwhacking and clearing the entire circle, trenching almost 1200 feet of feedline etc so there was a lot of sweat work done on that project. But on 160 and 80 where I have the tx antennas to use as a comparison, the specialized rx stuff just doesn't hear the weaker stuff. And it's not that I have a pristine can hear a pin drop low noise qth, esp on 160 - plenty of flare stack ingitors plus the usual powerline and smps junk. It's especially frustrating to hear all the glowing success stories of these rx arrays and how they make the dx just jump out of the noise and into your log... _ Topband Reflector Archives - http://www.contesting.com/_topband
Topband: LORAN, Radiolocation
Which does radiolocation mean? Radar or loran/GPS/etc. or both? Not obvious. Rick N6RK LORAN was a system of radionavigation, not radiolocation. Not the same thing. Radionavigation is just what it says, a system used to help navigate a moving ship, plane or land vehicle. It was a useful tool for ships trying to navigate through unfamiliar waterways. Radiolocation uses single a beacon, transmitting from a fixed point to help ships, planes or other vehicles arrive at a destination. The 160m radiolocation beacons were widely used to enable ships and planes to find oil rigs in the Gulf of Mexico. GPS has pretty much rendered both systems obsolete. It's a lot cheaper and easier to use a small handheld or dash-mounted device, linked via satellites, than to build, operate and maintain a high power MF transmitter and large antenna system similar to that used by an AM broadcast station. Don k4kyv _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: 8 circle: DXE vs Hi-Z
Their meaning with respect to gain as unimportant is due to the fact that the RX antenna is all about SNR maximization. A low noise preamp can fix overall signal weakness, if your rig's preamps are insufficient. 73/jeff/ac0c www.ac0c.com alpha-charlie-zero-charlie -Original Message- From: David Raymond Sent: Thursday, December 18, 2014 12:00 AM To: Don Moman VE6JY ; Topband@Contesting. Com Subject: Re: Topband: 8 circle: DXE vs Hi-Z My experience is similar to Don's outlined below. Both gain and noise figure are important in very low noise environments. In my own case, I have a noise floor from my TX array in the high -120s or -130s assuming a quiet atmosphere. A high RDF performance RX array often brings virtually no improvement. In my case, since the RX arrays lack gain, they often don't have the horsepower (gain) to reach down and hear the super low level signals picked up by the TX array. Switching from the TX antenna to the high RDF receive array not only fails to make the signal jump out of the noise (what noise?) but fails to hear the signal at all. In these circumstance both gain and noise figure become very important factors. 73. . .Dave, W0FLS - Original Message - From: Don Moman VE6JY ve6j...@gmail.com To: Topband@Contesting. Com topband@contesting.com Sent: Wednesday, December 17, 2014 10:53 PM Subject: Re: Topband: 8 circle: DXE vs Hi-Z Well I disagree that gain isn't important. Maybe you topbanders in the better areas of propagation can afford to throw away many db to get a better rdf, but that sure isn't the case up here in mid-northern VE6 land. I have numerous receive antennas including many beverages and Wellbrook loops (large area) and the Hi-Z 4-8PRO 8 element circle. They all work more or less as expected on the easy stuff and show reasonable directivity but when I need help for the weaker dx, there just isn't any signal there to work with. The beverages do the best of the bunch, they aren't anything special - typically in the 700-1100 foot range. With the many vertical structures I have there is no doubt their patterns are somewhat affected but they seem to work fine for Eu and JA bcb dx vs the loops and the 8 verticals. Not that this has been a good year for much of anything on the low bands in this area. The HI-Z was erected quite aways from anything else which involved bushwhacking and clearing the entire circle, trenching almost 1200 feet of feedline etc so there was a lot of sweat work done on that project. But on 160 and 80 where I have the tx antennas to use as a comparison, the specialized rx stuff just doesn't hear the weaker stuff. And it's not that I have a pristine can hear a pin drop low noise qth, esp on 160 - plenty of flare stack ingitors plus the usual powerline and smps junk. It's especially frustrating to hear all the glowing success stories of these rx arrays and how they make the dx just jump out of the noise and into your log... _ Topband Reflector Archives - http://www.contesting.com/_topband _ Topband Reflector Archives - http://www.contesting.com/_topband
