Re: Topband: Post contest season: TX antenna vs RX antenna cros-stalk. What do you do?
Hi Mark - I have not experienced K3 TX/RX antenna isolation problems with my station configuration. I expect that if there is an isolation problem with your rig's TX and external RX antenna routing/switching, that problem would be nearly impossible to quantify using your station's TX and RX antennas. The rig's TX/RX isolation would need to be measured on the bench, using good laboratory grade equipment. Perhaps, Elecraft can provide a list of expected isolation values that were measured for each of the TX and external RX antenna routing/switching configurations possible with the K3 and K3S. Those measurements would surely have been done during the rigs' design performance verification tests. GL 73, Terry K4RX ++ Hi Bill, I think this is not what I meant here; I also do use BPF's and the Front End Savers. The problem is that while listening to your receiving antennas, there is also some signal from the transmit antenna getting through thanks to the internal cross-talk of your rig's TX/RX relay. I was wondering what people do besides the obvious 'kill the TX antenna input during RX mode' ? 73 Mark, PA5MW _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Why do rodents eat coax?
All of my transmission lines are buried except for the single coaxial cable that feeds my 6m long-boom Yagi. After 15 years, I have not experienced any problem with varmints chewing on any of my buried cables, despite being located in the dense North Florida jungle. However, the aerial coax located along the boom of my 6m Yagi was attacked and destroyed on two occasions several years ago. The first time, some critter stripped away the BuryFlex outer sheath, foil and braided shield, and center dielectric along a 10-foot section of the feedline. That left only a skinny center conductor as a very poor transmission line. At the time I supposed that it must have been the work of nesting squirrels (tree rats), so I simply rebuilt the feedline harness for the upcoming Summer Es skip season. After a few months the problem returned and the coax was found stripped away again. I set aside radio operating for a while and began watching my 6m tower for evidence of the guilty party. To my surprise, I found the culprit to be medium sized woodpecker birds. Two or three birds would hang upside down under the Yagi boom and very efficiently strip away at the coax until the damage was done. I rebuilt the feedline harness again, but this time I installed all of the coax on the Yagi inside of protective grey PVC conduit. The conduit did increase the antenna wind loading, but I have not lost a transmission line to birds since then. YMMV. Terry K4RX W8JI wrote in part: Squirrels and rats can be a problem, but mostly my cable chew issues have been from raccoons. I used to trap them and deport them a few miles. Now I just I bury my cables. Even a few inches of dirt is enough. Where they come up out of ground, I sleeve them with cheap plastic sprinkler pipe. You can splice out the bad areas, but you have to bury, sleeve, or fix whatever is eating it. _ Topband Reflector Archives - http://www.contesting.com/_topband
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: Submerging variable caps in oil as substituteforvacuum variables
Dissipation factors for particular oils are found here: http://www.icrepq.com/icrepq'12/538-toudja.pdf I cannot comment on the accuracy of the data. Terry K4RX -Original Message- From: Topband [mailto:topband-boun...@contesting.com] On Behalf Of Tom W8JI The major issue with dielectrics is dissipation factor at 2 MHz, which affects losses and Q. Dissipation factor is not published all the time. I can't find dissipation factor for mineral oil. _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Shunt fed tower plus Marconi vertical phasing on 160 and80?
...and reasonable instrumentation and a good understanding of what is actually going on. Difficult or hard is a judgment call from one's own particular expertise and experience perspective. Antennas are a wonderful interest area of amateur and professional radio. Experiment and enjoy. Read good engineering books if you are interested in antennas. 73, Terry K4RX I don't know how deeply you understand directional arrays and networks, but you could probably make it work with a couple T-network tuners and some relays just by cut and try. It might take a little fiddling around listening to signals, but there will always be a combination of what you could do with a T network or two that would provide deep nulls. It is more cookie cutter to use series fed quarter wave elements with current feed (95% of people still do that wrong), but if you have a little patience and don't mind experimentation, you could certainly make it work. I phased dissimilar elements many times over the years, with the grossest mismatch a T phased against a shunt fed tower. All it takes is parts and patience. :-) 73 Tom All good topband ops know how to put up a beverage at night. _ Topband Reflector
Re: Topband: Beverage antennas - Ticks
Tom is correct. Ticks carry many bad blood bugs, both virus and bacteria. Here in buggy North Florida tick fevor is very common and it is not Lymes disease. Mountain tick fever, Texas tick fever, Southeast tick fever, the list goes on... Ticks are also the vector for spreading deadly Cytauxzoonosis to domestic cats in North Florida sourced from wild Bobcats to deer... Terry K4RX -Original Message- From: topband-boun...@contesting.com [mailto:topband-boun...@contesting.com] On Behalf Of Tom W8JI Sent: Monday, July 23, 2012 4:04 PM To: donov...@starpower.net; topband@contesting.com Subject: Re: Topband: Beverage antennas Ticks carry many things, some that doctors are not familiar with. ___ UR RST IS ... ... ..9 QSB QSB - hw? BK
Topband: Radial Wire Source
Consolidated Electronic Wire and Cable http://www.conwire.com/ sells bulk quantities of solid copper tinned wire, available in many AWG sizes. Prices seem to track copper commodities prices.image that. 73, Terry K4RX ___ UR RST IS ... ... ..9 QSB QSB - hw? BK
Topband: Antarctica 160m
12-Mar-05 R1ANN de K4RX ___ UR RST IS ... ... ..9 QSB QSB - hw? BK
