Gain is the effect produced when either more dipoles are used in an antenna (such as a Collinear) or if extra elements are added (as in a Yagi). What happens is that the shape of the pattern is altered to send more radiation in a particular direction and less in others.
The term dBi refers to gain over an Isotropic source and is really a theoretical term. It would give a radiation pattern in the form of a perfect sphere emanating from this source.
The expression dBd refers to the gain produced by a half wave dipole, which as stated above gives a 360° shaped pattern. The difference between them is 2.14 dB, which the dipole produces above the Isotropic source. An increase of 3dB means a doubling in gain, therefore a 3dBd gain antenna has twice the gain of a half wave dipole and a 6dBd antenna has twice the gain of a 3dBd antenna.
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'Collinear' literally means 'one above the other' and usually refers to several dipoles mounted above another and held within a non-conductive tube of Glass-Fibre or similar. The pattern produced is still 360° in the horizontal but much narrower in the elevation depending upon the number of dipoles used. This results in increased gain, typically 3dB or 6dB above that given by a single dipole.
'Yagi' antenna is a technique of fixing a passive element alongside a dipole to act as a reflector and then also attaching a number of parasitic elements to the other side, each slightly shorter than its predecessor. The effect is to concentrate the radiation pattern into a cone shaped beam, concentrating the RF Power into one direction and giving a much higher gain figure.
This is commonly asked but is not easy to state definitely because so many different factors are involved, mainly these are: the height above ground the antenna is installed, the transmit power used (less any losses in the system taken up by feeder cables, filters etc.) and the gain of the antenna used. What should be kept in mind however is that all VHF and UHF radio propagation is essentially 'line of sight' that is if the antenna site is at all visible to the outlying mobile unit, then the signal will usually be strong enough. This can vary between one or two kilometres to some 30 km (20 miles) or more.
This is another question that has different answers, We offers a good range varying from RG213 which is similar to that fitted to most antennas in short lengths, to the Low Loss, Foam Dielectric types of ½", 7/8" and 1 ¼" sizes that will reduce losses. Basically the larger diameter cable the lower the losses, also losses increase the higher in frequency you go so the need for larger cables also increases.
Nominally all connectors fitted to antennas and feeder cables are supposed to be 'weatherproof' but it is a brave installer who would trust to this. Normal practices today is to first use self-amalgamating tape across the whole of the connector joint and ensure it leaves no voids or sharp edges, then follow this with two layers of good quality electrical insulating tape overlapping by 50% with each turn. This in itself is good enough for most.
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An antenna plot tells you where the radiation is concentrated. Patterns are usually referenced to the outer edge of the plot, which is the maximum gain of the antenna. This makes it easy to determine other important antenna characteristics directly from the plot.
Most antenna users are interested in the directivity or beamwidth of the antenna. This is usually referred to as the "half-power" or 3 dB beamwidth, the points between which half the power is radiated or concentrated, and specified in degrees. As an example, the typical half-power beamwidths of a 3, 6 and 10 element Yagi are 60°, 40° and 30° respectively.
Beam width is a function of design, which has to incorporate all the relevant (and related!) factors to achieve the optimal result: gain, VSWR ( voltage standing wave ratio), front-to-back ratio, operating frequency, & bandwidth. Antenna Experts antennas have excellent operating characteristics in that they are broadband, have a VSWR of 1.5:1 or less, a high front-to-back, and very consistent gain across the operating frequency.
If you require more coverage, choose an antenna with more beamwidth. However, more beamwidth can imply a lower nominal gain at the same frequency than an antenna with a narrow beamwidth.
This is the first major delineator of antenna selection. The only way to increase gain is to concentrate power in a narrower beamwidth. The narrower the beamwidth, the greater the gain of the antenna.
A Yagi antenna is basically a standard half-wavelength antenna with additional elements placed in front of it to focus the energy for transmission in one direction. The more directive elements, the narrower the beamwidth and the greater the gain. In other words, gain is simply how you focus the radiated energy at the transmitter and how you focus the 'ear' of the receiver.
Above 400 MHz, a 3-element yagi will typically have 6 dBd gain, depending on the physical size of the elements, the boom, and other design characteristics. Adding additional elements will increase the gain. (Adding 3 dB is doubling the gain.) So the 9 dBd. gain yagi has twice the gain of the 6 dBd. yagi.
Omni antennas radiate transmit power (the signal) in all directions (360°) and listen for incoming messages from all directions. Omni antennas, therefore, do not send a signal as far as a yagi antenna of the same gain.
A vertical omni directional antenna is often used for line-of-sight communications with mobile stations spread out in various directions usually restricted to the horizon. If greater performance is required, using a collinear type of omni that decreases the vertical beamwidth and hence concentrates more power on the horizon where it will be most beneficial can increase the antenna gain. Increasing the length of the antenna (adding vertical elements) will increase the gain of an omni antenna.
Lightning protection must be examined from four distinct directions. First off, the place where the antenna is mounted (such as on a tower) is important. Then there must be input protection from the lightning strike itself, typically in the form of a huge and rapid build up of voltage and current at the input to the radio. Thirdly, a proper ground system must be employed to rapidly conduct the lightning bolt energy away from the radio.
If at all possible, don't mount your antenna on the highest building or tower. Place it a few feet lower and hopefully the fickle lightning bolt, if it generates a direct hit, will not discharge through the antenna. Furthermore, the boom or mast should be grounded to the mast or tower. Don't forget to ground guy wires that are used on stabilize towers. They are just as likely to be hit since they extend over a wide area around the tower.
The most important lightning protection is good low impedance Earth/ground connection to the associated equipment. The Earth ground connection should be a copper plated rod preferably at least 3-4 meters in length driven into the ground. This ground rod should be located as close to the equipment as possible, typically just outside of a building at the entry point of the antenna feed-lines.
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I be no expert but I suspect that perhaps an efficient antenna on 400Mhz would be too large to launch. Perhaps someone else could comment? I did have a Ublox Neo6M chipset with an amplified quadrifiler antenna that would get
a reasonable GPS lock while in my basement! I dropped it and that was the end of it. The chips have been surpassed and more imporatantly the antennas went out of production.
The CSG shop still has the chips listed on pages 6 and 7: https://www.csgshop.com/category.php?id_category=16&p=6 Kurt
Found this. Might help answer your questions:
https://jcoppens.com/ant/qfh/calc.en.php
Not sure if this also applies to quadrifilar antennas, but on a 1/4 wave whip antenna, small errors in length produce insignificant effects on antenna performance, so optimizing for the middle of the band works just fine.
Not sure if this also applies to quadrifilar antennas, but on a 1/4 wave whip antenna, small errors in length produce insignificant effects on antenna performance, so optimizing for the middle of the band works just fine.
Yeah, A long nosecone with a nosecone mounted 70cm or even a 2meter GPS tracker is a nice position to be in. Can even add a counterpoise or "tigertail" to turn the vertical antenna
into a vertical dipole. For sport fliers don't bother but if going to be flying in an extreme regime might give one a little edge. For instance another element on the 70cm
Beeline GPS might improve the situation a bit. Here's a representative site that explains it: https://w3atb.com/tiger-tail-antenna/
Again, If one's rockets aren't expected to go more than 2 miles I wouldn't bother with this with any tracker.
This link is about Quadrifiler antennas on 70cm: https://uuki.kapsi.fi/qha.html There might be an advantage on the receiving end with being able to decode positions from
a tumbling rocket but I don't think you would be able to fit it inside of a rocket on the tracker end unless it was a large project. Kurt
Every antenna has a bandwidth that they will work over. At 435Mhz a quadrafiler antenna should work over several MHz just fine.
I'm using a Crossed Moxon Array on 435 MHz for tracking rockets. I've had success with flights to 20,000 feet. It should work higher that is just the highest flight I have tested it with. Mine sits on a PVC stand about 6 feet tall and I don't have to touch it during a flight. I use a 1/4 wave vertical in the nosecone for the rocket end of things.
https://www.oocities.org/w9bci/VHFUHFSatelite.pdf
Every antenna has a bandwidth that they will work over. At 435Mhz a quadrafiler antenna should work over several MHz just fine.
I'm using a Crossed Moxon Array on 435 MHz for tracking rockets. I've had success with flights to 20,000 feet. It should work higher that is just the highest flight I have tested it with. Mine sits on a PVC stand about 6 feet tall and I don't have to touch it during a flight. I use a 1/4 wave vertical in the nosecone for the rocket end of things.
https://www.oocities.org/w9bci/VHFUHFSatelite.pdf
That is what my intuition was telling me so it's comforting hearing it from someone else with more knowledge on this subject than myself, which is not hard. Still having a firm answer is what I am hoping to get. BTW one of the flights I am hoping to have this rig up and running on will have a Raven 3 and your new Mag switch on board.
Good article on the how to make a Quadrifilar Helical Antenna (QHA or QFH), the tiger tail is not something I had considered so I will have to dig a bit deeper. Did you notice the author of the article used one of these antennas in an amateur rocket https://haisunaata.avaruuteen.fi/. It's not uncommon for me to fly in the 3+ mile range, although I am also hoping that this antenna might perform well enough for some higher alt flights I have planned in the 40-60K range. We will see. As I state I will have my yagi going as well so this is more a backup.
Good to hear another opinion on the range or accuracy of antennas. The trackers I will e using with this antenna are the TeleGPS units, which have a 1/4 wave whip vertical antenna on them.
Nice Terry, That looks easier to build than a Quadrifiler. Do you recover most of the positions on descent? I've noticed with simple antennas like a stock wire on a 70cm BeelineGPS and an aftermarket duck antenna, there are missed positions via Rf with the long fall under drogue from high up 8k or more. These losses which vary from flight to flight are occurring well before loss of signal. I suspect (especially with the 16mW BLGPS) that changes in polarity with the tracker flopping around under drogue were responsible for the position losses.Along with the Crossed Moxon Array that Terry recommended, others recommended a Texas Potato Masher as well as the Eggbeater, as possible options for this application.
Worst case I've seen was loss of two positions that would be over a 15 second span and then positions resume. I've heard one missed position too. Easy to observe with the once every 5 second APRS transmission. Sometimes makes me sweat
but breathe a sigh when reception returns. Another reason why I like to blow the main out as high as practicable because with the slower descent and a more or less vertical position of the tracker antenna, packet reception is much more reliable.
That's what really counts to have a successful recovery. Get as many positions as possible down low before Loss of Signal (LOS)
I just might look into making one of these Moxon arrays for the fun of it. Seems simplier than a Quadrifiler ground station. Learned something today. Oh also learned that if one is going with a Quadrifiler ground station, since the transmitter is using a vertical polarized antenna it doesn't matter if the receiver Quadrifiler is Right Hand Circularly Polarized or Left Hand Circularly Polarized.
Only way to improve receiving is use the best antennas for the job on both ends, more power output on the tracker and a good quality of receiver. Thanks again for posting. Kurt KC9LDH
https://aprs.fi/#!mt=roadmap&z=11&call=a/QCRS&timerange=&tail=