Antenna for VHF - Page 1
Forum section: electronics / rf-microwave

author: jtronix
author_rank: Regular Contributor
timestamp: April 23, 2017, 11:28:18 am
content: I would like to buy antenna for my walkie talkie my transmit frequency is 145MHz and Receive is 155MHz.From where i can buy the antenna and which type of antenna is good for long range?

author: ChristofferB
author_rank: Frequent Contributor
timestamp: April 23, 2017, 12:55:16 pm
content: Well 145MHz is right in the 2m band, so any ham-site could sell you a decent antenna for that. I suppose it could receive on 155 MHz as well, but it may be an advantage to have a separate transmit/receive antenna.When you say long range, do you have a single station you want to talk to, like a repeater or something? then you could go for a directional antenna like a yagi.If it's a handheld station, a 2m yagi might be a bit large to carry around. how about a standard whip antenna? Or is that what you already have?

author: jtronix
author_rank: Regular Contributor
timestamp: April 23, 2017, 02:15:10 pm
content: Thanks for your suggestionI'm going to use it with DRA818V module. At this moment i' not sure about repear whether i'll need or not and i'll decide after testing. Can you llease suggest how to use repaer for extend signal range ??Does whip antenna is good for long range (5 km)??

author: German_EE
author_rank: Super Contributor
timestamp: April 23, 2017, 07:10:38 pm
content: Are you sure about that 155 MHz frequency because it's outside the amateur bands?Anyway, grab an SO239 socket and five lengths of coat hanger wire each about 20 inches long. Solder one length to the center pin of the SO239 and the other four to each corner of the socket (you may need to use solder tags here). Bend the four groundplane lengths down till they are about 45 degrees from horizontal then trim the center length of wire using an SWR meter, it should end up about 19.5 inches long.http://www.hamuniverse.com/2metergp.html

author: jtronix
author_rank: Regular Contributor
timestamp: April 24, 2017, 02:12:26 pm
content: Today i'd call antenna manufacturer and ask for 134 to 174 MHz antenna. but he replied me that 134 to 174 MHz antenna is not possible to make you can have max 5 MHz bandwidth that means if the antenna can be made of from 145 MHz to 150 MHz or 150 to 155 MHz ,...etc.can someone comment on thishow antenna design isCan we make it at home?

author: German_EE
author_rank: Super Contributor
timestamp: April 24, 2017, 04:56:24 pm
content: The 5 MHz bandwidth sounds about right, that's for a reasonably efficient antenna. Outside the working frequency the antenna will still work, just not very well. As an example I used a groundplane antenna like I previously described to work 2m FM when I lived in the UK, the same antenna was used to receive air band signals from the local airport (108-137 MHz), it worked but it should have been a lot longer.

author: PA0PBZ
author_rank: Super Contributor
timestamp: April 24, 2017, 05:58:52 pm
content: A discone antenna can be very broadband but has no directional gain, if you want that you can look at a log periodic antenna. Both can be made to cover more than a 1:20 frequency ratio. However, a simple reflector - dipole - director antenna will work fine for 145-155 MHz.And since no one brought it up yet, you are not allowed to transmit on 145 MHz without an amateur radio license, and not on 155 MHz without a proper license for that and certainly not with home brew equipment.

author: LaserSteve
author_rank: Super Contributor
timestamp: April 24, 2017, 09:41:36 pm
content: FYI FWIW:https://www.eevblog.com/forum/rf-microwave/looking-for-long-range-wireless-audio-transmitter-and-receiver/Steve

author: GW7MGW
author_rank: Newbie
timestamp: April 25, 2017, 12:48:58 am
content: Some times we get surprising results from an aerial, I was on a mountain and living in a container, to be able to get BBC world service during the day I threaded a wire through the vent in the container and ran it to a pole. I had expected to go outside that night to use 2M set to talk to locals, but found I was locked in, and so I connected long wire to my 2 meter radio and tried at a very low wattage to talk to locals.It worked, it should not have really worked, and was not too good for the radio but my FT290R worked well.Aerials are odd things specially on receive, I was using a HB9CV and I was told the military were going to transmit TV in the near future, I had a TV for my computer, so tried plugging in the aerial to see what I got, and there was a signal very weak but there, so rotated aerial got it a little better but still poor, anyway dinner time so went to get dinner and walked past a open door to a room and noted he had a TV showing same program but far better, I stopped and enquired, he had left the built in aerial on his TV and I was picking up a signal from his video recorder.So if the aerial is good for the transmit frequency you may still receive well out of the band the aerial is designed for, again 2 meter this time in the UK, car fitted with halo aerial and 7/8th whip, using a FT290R with hard wired MM 30 watt linear amp I was going to talk to another ham on the way home using side band and compare the two aerials, his aerial was horizontal and as I drove further and further away the halo was doing best, he went for tea as I reached about 50 miles away, but another ham joined in, the first one had left his radio on and I continued back towards North Wales now around 90 miles away and now it seems the first station was hearing me again. However the odd thing was now the 7/8th whip was better than the halo. It seems as distance increases being horizontal or vertical becomes less important and the gain of the aerial is more important.In Wales the mountains limit distance, but in Suffolk at some times you could get huge distances. All down to weather, however same frequency on the Falklands and where in UK 30 to 300 miles, in Falklands 10 to 30 miles, we rarely heard the East Island but not really that far away, with one exception Port Louis could be heard all over the Islands even with a hand held. Love to know why, but that one settlement had a huge range.So there are two very different radio contacts, you get the chance contact maybe off the e layer 100's of miles but only once in a blue moon, and the guaranteed contact where what every the weather you can communicate. With RAYNET the latter is important, and we would test where we could reach and often have either a repeater or a person to repeat the messages. Long time ago I used packet radio, because you could use other peoples radio to forward the message you could do really long distances, however you typed the message, put on the kettle, made coffee and then sat waiting for reply, it was like watching paint dry. As internet arrived packet stopped being used.

author: Electro Fan
author_rank: Super Contributor
timestamp: April 26, 2017, 04:29:29 am
content: probably not the least expensive product but this design will work well on 2M and also 70cmhttps://elkantennas.com/product/dual-band-2m440l5-log-periodic-antenna/

author: AG6QR
author_rank: Frequent Contributor
timestamp: April 26, 2017, 05:38:48 am
content: You have to define your goals a little better, I think.Is this antenna to be used handheld? Or mounted to a building or other structure? Or used in a vehicle (permanently? or temporary magnetic mount?)Do you want to transmit and receive in a particular direction, or do you want something that works equally well in all directions?How big and heavy can you tolerate? How much money?Like others, I'm suspicious of transmitting on 145MHz and receiving on 155MHz. For most ham radio repeater use, the difference between sending and receiving frequencies in the 2m band is usually 0.6MHz (600 kHz). This is close enough that one antenna does both jobs.Regardless, most antennas work well for receiving well outside their ideal transmitting band. That's because receiving is largely about signal-to-noise ratio, and when an antenna is poorly tuned for a particular frequency, it usually attenuates both the signal and noise relatively equally, so the SNR remains acceptable. Transmitting, on the other hand, is all about efficiently radiating all the power delivered to the antenna, and this is mostly about making the impedance of the antenna match the impedance of the feed line. The impedance of an antenna is usually very much frequency dependent.In practice, all of my antennas that are optimized for transmitting on the 2m ham bands work well for receiving in the aviation band (118MHz-136MHz) and the weather band (Approx 162 MHz).For a walkie-talkie, most people want a relatively small, omnidirectional antenna. One that is rugged and flexible is usually nice. The Diamond SRH77CA is a good general purpose antenna for the 2m ham band. Of course it's not magic, and there are similar antennas made by other manufacturers. Be sure to get an antenna that matches whatever style of connector you have on your walkie-talkie.http://www.hamradio.com/detail.cfm?pid=H0-006297But there are other possibilities, depending on how you want to use the antenna. A 1/4 wave magnetic mount antenna with a decent coax will perform very well mounted on a car roof. A yagi will perform very well if it is pointed at the station you want to contact.At these frequencies, there is tremendous value in getting the antenna up high and in the clear. Put a mediocre antenna up 20 meters in the air, and it may start to perform quite well.

author: Lord of nothing
author_rank: Super Contributor
timestamp: May 10, 2017, 01:00:35 pm
content: Where are you from?Maybe a Company who build stuff in your Area is cheaper than an European / American/ Asian Antenna.

author: BigBoss
author_rank: Regular Contributor
timestamp: May 16, 2017, 12:28:59 am
content: A small Yagi-Uda antenna with a folded lambda/2 dipole with few non-folded lamda/2 dipols at the front of that dipole will work a quite reasonable wide-band antenna.You can also use an old TV Band-III antenna, I'm sure it will work at that frequency with a bit loss.