Does $28 whip antenna support 10hz -1GHz?(with ebay link) - Page 1
Forum section: electronics / rf-microwave

author: nicegirl
author_rank: Contributor
timestamp: March 18, 2022, 06:15:39 pm
content: https://www.ebay.com/itm/114530317789I found above antenna with main parameters:QuoteDoes this whip antenna really support 10hz -1GHz?

author: Joel_Dunsmore
author_rank: Regular Contributor
timestamp: March 18, 2022, 07:11:48 pm
content: well, it does telescope. I doubt very much it has 1.5 SWR much below about 100 MHz. These type of "vertical" antenna are typically matched where length equals 1/4 wavelength. So 1 GHz is 30 cm full wave, or 7 cm 1/4 wave, and 100 MHz is 75 cm 1/4 wavelength. So it could be matched over that range (matched meaning good return loss or low SWR). I guess much below 100 MHz it won't be matched, but it is at least DC coupled so it could work with poor matching and won't have the gain it does at other frequencies.But, I see you have asked several questions about making something that appears to be a receiver for modulated signals. It might be helpful to describe your overall project to help others (like me) understand the context of your questions.

author: cdev
author_rank: Super Contributor
timestamp: March 21, 2022, 01:21:07 am
content: Of course for 10 Hz, no. Price is irrelevant. That antenna is just a telescoping whip connected to a coaxial connector. Its not a broadband antenna as the ad might imply.At the lower extent of that range its going to be very inefficient of course.A monopole that is electrically much longer than a quarter wave is going to have a very lumpy antenna pattern based on the tendency of a long wire (electrically) to act like a traveling wave antenna, it will receive and transmit with any gain towards it's far end. The wavelength of a 1000 MHz signal is going to be so short that that antenna is going to be determined by the addition and subtraction of the length.In my experience a long wire less than I wavelength above the ground on HF tends to be off its end to some extent. Of course this is nothing like a vertical.If you want a predictable pattern use a quarter wave monopole. A quarter wave at the proposed design frequency.

author: cdev
author_rank: Super Contributor
timestamp: March 21, 2022, 02:16:51 am
content: I would make aplanar disc antenna, or a verticalbowtie..The planar disk is easiest, and works well..Use two large pizza plates. Use coax that allows you to connect the shield to the bottom disk. This is called an infinite balun.Use two pizza plates attached to a piece of flat wood.. like a figure eight. Visualize a double spatula.. Google planar disk antenna.Make sure the coax shield is bonded to the bottom disk at at least the ends, ideally it should be bonded several times.. this reduces noise.. If you dont do this then you need to use a balun at the center for best performance, but the conventional balun probably will hurt performance at high UHF frequencies (above 1 GHz) (unless you choose the balun very wisely)The infinite balun, basically uses theembedding of the feedline inside one of the two arms of the dipole to keep the signal balanced, this acts like a balun. You should also use at least two or three ferrite split beads on the feedline after it exits the bottom of the antenna. Actually the more spit beads you can use there on the feedline, going down, the better. They help with noise a lot.Then lower frequency limit this antenna works at is determined by the size of the disks which ideally should be equal. Pizza pans from dollar stores are good planar disks for this antenna. The two disks should be as close to one another as you can without them touching. You solder (or bond) the tip to the coax center and the bottom to the shield, and for best results it should be soldered all along its length successfully. (But this is difficult without causing problems with the coax impedance especially with foam coax.. Teflon dielectric is better for this kind of soldering)If you cant do that use copper tape, cover the bottom part of the coax with copper tape.The most critical thing to get right is the point where the two discs almost touch one another. The connection to the coa there should be as short as possible, and you should make it your business to bond the two connections to the coax well. Use copper tape if your pans are aluminum to provide a solid point for your soldering. Its essential to use a solder bond. Almost all builds of these antennas you see use two disks but an upgrade to the planar disk can be effectuated by using four disks. make two slits in two disks so they can be joined to make a ball and then do it again for the bottom. In other words, make an X out of the two disks. Then use copper tape and solder to electrically bond the point where the two disks meet.Do this again on the bottom. What I wrote above about the infinite balun applies in the same way with this variant. It will work much better with care taken to ground the shield well. I would use low loss semi-rigid coax with its braid accessible on the outside for this antenna.Ive made several of them (one just uses aluminum foil and cardboard and copper tape and is perfectly flat like a poster) and they work well and are easy to hang from a hook or something on the wall or (ideally) ceiling. A large planar disk antenna can work well at fairly low frequencies. It seems to have a tiny bit of gain over a dipole at its resonant frequency but has the advantage of being broadband and having its pattern, its main lobe at the horizon. Use a decent feed cable and the performance can be good. Better than the usual discone at the horizon, and its more broadband too.(It seems like what you are asking about is a very broadband antenna. Such an antenna is so hard to make it might as well be impossible in terms of feasibility when it comes to low frequencies as they demand either very large antennas or innovative strategies far beyond the antenna youre describing.)That monopole antenna was kind of the minimal antenna and in the 1980s it was provided with scanners (I got mine with a RadioShack scanner I bought when I was a kid. The scanner is long gone but I still have it.) because it "kind of worked" somewhat on almost anything. But its not at all an adequate antenna for anybody who wants to be successful at receiving a wide number of signals. The p[lanr disk is a real broadband antenna that will serve you well at frequencies above its lower cutoff frequency well up into the UHF range. The higher you can get it above the average terrain, the better. The curvature of the earth limits your range for that reason at VHF and UHF. This is illustrated well by a program called "splat" which is used by radio and TV boradasters and hams to determine the height and to some extent gain needed to establish a link between different stations.

author: max-bit
author_rank: Frequent Contributor
timestamp: March 24, 2022, 02:37:31 pm
content: $ 30 for a standard telescopic antenna?It's just a scam and that's about it.

author: cdev
author_rank: Super Contributor
timestamp: March 24, 2022, 06:03:45 pm
content: Are they really charging $30 for that? Well, I guess a fool and his or her money are soon parted, as they say.I have seen similar antennas sold on ebay for $3 or even less.Hey, that reminds me, a cheap 4:1 balun sold top allow use of 300 ogm twinlead with coax cable can be used as a central T with wire to make a broadband dipole. Make two rings one on each side (wire coat hangers work well for this) and put the rings on each side..You can make a much better balun using the TLT methodoloogy..Actually you can do much better.. One of the users here (Tiscoli) His name is I think Tim, He is very savvy when it comes to RF transormers and electromagnetic theory and applications.. He's one of the most helpful people here, actuallyHe made a bowtie antenna for his own use thats built around his own design broadband balun and the two "ears" are bent into a bowtie shape that makes this an ideal antenna for broadband.. And its likely quite cheap and easy to make using coat hangers..From my own work with planar disk and bowtie antennas I suspect it performs very well.. To get vertical pattern turn it sideways. with the feedline exiting to the side.. Super simple, but works great.. And its quiet.. This works much better than the antennas many people use for this kind of general VHF/UHF reception.. It works really quite well for the FM broadcast band and HDTV (if sized appropriately.)The bowtie or planar disk is far superior to a dipole.. However the balun and a good one becomes the limiting factor.. as well as the height above ground. Such an antenna is semi directional with the most gain being broadside to it. If you put it up like a T then the polarization is horizontal and if you put it up like a figure 8 then the pattern is vertical.A bunch of times I have posted a 1:1 balun design based on the elecraft BN-2 .. That balun has a switch that lets it put the windings in series or parallel..allowing either a 1:1 or 4:1 impedance ratio..he bowtie impedance likely ends up being in between 50/75 and 200/300 ohms so that is good to have.that balun would be a good choice.. But use a small one if you want good response at UHF. You can build the BN-2 clone with magnetics that allow a response well up into the GHz range if you make it very tiny with thin, insulated wire. (I often use the wire from Ethernet cable which is usually good for RF, as insulated wire goes) Note: I am describing a receiving antenna..The balun will make this antenna quiet and quite good for a very wide range of applications.. I suppose one could use it for transmitting (if licensed appropriately) but the thin single stranded Ethernet wire is not suitable for any amount of power above QRP, at the most a very few watts.Don't use the thin coax unless its very short or you will lose the upper frequency range in the feedline.