One antenna with band switching between  2M (144MHz)  and 70cm (440MHz) - Page 1
Forum section: electronics / rf-microwave

author: JoeyG
author_rank: Regular Contributor
timestamp: July 26, 2024, 12:20:45 am
content: HiI am thinking of a small handheld design where I can have one antenna and switch in passive L's and C' to band switch the antenna from 2M to 70cm with a or more FETs.Has anyone come across PCB design that can do the band switching or do I need a band switch for different antenna (not prefered).

author: MarkF
author_rank: Super Contributor
timestamp: July 26, 2024, 12:37:25 am
content: I'm not a ham radio guy, but you may be able to find something onAlan Wolke's YouTube channel.

author: Andy Chee
author_rank: Super Contributor
timestamp: July 26, 2024, 03:24:59 am
content: Band "switching" is unnecessary.Just use a low pass LC for 144MHz, and high pass LC for 440MHz, and leave them both permanently connected to their respective antennas.This device is called a duplexer and can be homebrewed or purchased from any ham radio shop.

author: wasedadoc
author_rank: Super Contributor
timestamp: July 26, 2024, 07:41:56 am
content: Quote from: Andy Chee on July 26, 2024, 03:24:59 amThe OP clearly statedoneantenna.

author: Andy Chee
author_rank: Super Contributor
timestamp: July 26, 2024, 08:12:04 am
content: Quote from: wasedadoc on July 26, 2024, 07:41:56 amWhether it's a single antenna being split into separate 2m and 70cm transceivers, or a single transceiver being split into separate 2m and 70cm antennas, the low & high pass LC filters can remain in circuit permanently connected. No switching is necessary.

author: wasedadoc
author_rank: Super Contributor
timestamp: July 26, 2024, 09:29:19 am
content: Quote from: Andy Chee on July 26, 2024, 08:12:04 amWhile that is true both cases involve 3 entities. The OP wrote "a small handheld design" and "one antenna". Only 2 entities.

author: Andy Chee
author_rank: Super Contributor
timestamp: July 26, 2024, 10:18:42 am
content: Quote from: wasedadoc on July 26, 2024, 09:29:19 amSwitching seems to imply the existence of a 3rd entity.Otherwise obviously I have no idea what the OP's entire proposed system interconnect is.

author: CaptDon
author_rank: Super Contributor
timestamp: July 27, 2024, 02:05:41 am
content: Are there not already about one hundred different antennas that are 'dual band' for 2M and 70CM band with either an SMA male or female connector as well as BNC types readily available???

author: A.Z.
author_rank: Super Contributor
timestamp: July 27, 2024, 04:25:32 pm
content: Quote from: JoeyG on July 26, 2024, 12:20:45 amor... no switching at all; consider this ideahttps://vk2zoi.com/articles/dual-band-half-wave-flower-pot/now, while the above is probably too long for a handheld, it may give you some hints

author: iMo
author_rank: Super Contributor
timestamp: July 27, 2024, 04:44:08 pm
content: Today one would need the diplexer (written with "i") when he/she/it wants to use duplex (written with "u") mode operation with the handheld transceiver.You have one single "multiband antennna" (2, 3, 4 etc. bands in one single antenna, one connector) and the diplexer inside the radio separates the signals based on the frequency (none switching involved), while you receive and transmit at the same time "cross-band".This mode is used rarely in HAM world, however, therefore there is only a couple of TRXes with this functionality on the market (the most expensive ones).For a dual band antenna in a "simplex" mode you would not need diplexer or switch.As it has been indicated above, there are dozens of various types of "multiband antennas" for VHF/UHF bands available either for purchase or as a DIY build. It is rather broad and difficult area to elaborate here, you would need to search and study a lot.. Best is to use a commercial multiband antenna for the bands of interest. Most of them are fakes (those for $3-$10), but there are genuine ones still available.73PS: I own the handheld which can do full duplex, and I made only 2 single QSOs ever, as an experiment with other HAM who had the appropriate equipment, where we did it as an experiment, it worked nice, I have to admit.. You have to check your local regulation btw., not everywhere is the duplex as well as simplex "cross-band" allowed by the authorities, imho..HAM operators on this bands use simplex only, thus unless you would organize and prepare such a QSO in advance you will not be lucky with the duplex mode..There is one exception - the HAM communication over LEO satellites, where it could be used (if allowed by the local authorities). But for that you would need multi-element Yagi antennas, with circular polarization, usually one Yagi for a band (ie. 70cm uplink and 2m downlink or vice versa), both Yagis mounted on a single boom (like "X").

author: jonovid
author_rank: Super Contributor
timestamp: August 02, 2024, 03:15:06 pm
content: just google 2m and 70cm dual band J-pole wire antennaband switching is unnecessary.

author: David Hess
author_rank: Super Contributor
timestamp: August 02, 2024, 08:07:41 pm
content: 2 meter antennas usually work acceptably at 70 centimeters without doing anything special, so the 2 meter and 70 centimeter RF ports just need to be combined with a duplexer.

author: metrologist
author_rank: Super Contributor
timestamp: August 02, 2024, 09:47:03 pm
content: Quote from: iMo on July 27, 2024, 04:44:08 pmIt is quite easy and inexpensive to make a crossband repeater using two radios (cheap Chinese HH, for example) with the audio I/Os connected together and VOX mode. For example