IC-705 Antenna switcher Last updated on: March 12, 2026
IC-705 projects
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See also Triplexer THIS PROJECT IS CURRENTLY UNDER TEST, INFO HERE IS PROVISIONAL ! As expected, results were disappointing on the 70cm band with the original relays I used, (not shown here) that I had to hand. Consequently, I ordered some more suitable "RF" type relays and a new PCB was ordered. It arrived around 5th Jan '26. The Schematic is near identical. Initial results excellent: <0.2dB loss on all outputs. Cross talk graphs will be uploaded soon. Details below: |
This project is for an ICOM IC-705™ to enable automatic antenna switching. Since the IC-705 has only one antenna connector, changing to HF, 6m, 2m or 70cm band antennas is a bit of a nuisance. This project automatically switches between these 4 bands using Blue Tooth and switching 4 relays. This allows the use of separate switched antennas. In addition, a 5th relay operates when PTT is active on the IC-705. The black relays I had in the junk box used in the original Proto build (not shown) were a gamble, but tried them out. Result was poor on 70cm and 2m bands. This new version using better "RF" style relays has been built. (Thanks to Richard, VE2DX, for suggesting these relays) Losses on all bands (when selected) is <0.2dB In addition, a display shows the current Frequency, band in use, Filter in use and current Mode in use. Also five LED's on bottom edge show which band is active, plus the PTT output. This layout may not be suitable for some setups mechanically, but a front panel OLED display could be fitted to the available I2C connector. (Software has not been done for that) It's not really mandatory to have a display of course. The LED's indicate current band selected and if PTT is active. |
PCB info for those interested. The Schematic is here updated relays. Note, on this board, the UHF relay isolates the other 3 bands when selected so no long tracks or 'stubs'. Feb.. 9th: New PCB arrived and loaded V1.1a, see picture below. PCB Overlay showing values of components Bill Of Material (BOM) The software is here (contact me, vk3pe QRZ.com) When this project is built and you have programmed the TTGO module, you need to setup WiFi (do a search for the TTGO) in the IC-705. Power up the board. Power up the IC-705. Press Menu/SET/Blue tooth Set/Pairing-Connect/Device search. Then Set "Auto Connect ON". This will give you the info on the TTGO. Normally "CIV_BT_IFC" To connect, press it. After that initial set-up, the band switch board should be powered up before the IC-705 and the IC-705 will automatically find the board and connect. NOTE there are NO part by part build instructions. The assumption is you have some building experience.
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Below, is a picture of the updated V1.1a PCB and new relays. It is 100x100mm, double sided copper, from the usual Chinese PCB houses. Note, the un-loaded section of the PCB is for band decoding which might be useful if an external PA and LPF is used on HF for example. There are also outputs for the other bands, not just HF, all being active low using an ULN2803 device.
Relays used are OMRON 'G6K-2P-Y'. 12v type, through-hole. I found cheapest source to be on Aliexpress™. These should be adequate for the 10W of the IC-705. Be careful when buying these relays, very similar types do not have the coil polarity correct. Check Data sheets! It's also possible to use 5v relays as there are a couple of links on the PCB to allow use of 5v. Version 1.1 PCB The section not loaded is for optional individual Band output switching (active Low) See Sch. The top BNC socket is from the IC-705. On the right, from top is 70cm, working down to HF. Bottom relay provides PTT out on SPDT contacts, all isolated from GND. ie C, NO, NC. I plan to mount the PCB into a case, probably made from PCB material, with holes cut for the BNC sockets, plus the LED's on a front panel. Actual TFT display is not that important for me. If I did this again, I might have had 2 PCB's, one for the TTGO and one for the relay switching. That adds to cost though. An alternate mounting method is to mount the PCB vertically behind a front panel, so the TFT can be seen. And mount the LED's also vertically, to poke through the front panel. Alternate 'vertical' mount BNC sockets could then be fitted on the rear of the PCB.
The PCB is 100x100mm in size, double sided copper. The display is a little washed out, here is a better view of the display which is part of an ESP32 "TTGO" board. NOTE the display of current Mode and Filter#. The GREEN section is to show Rx and Tx mode, the latter is in RED.
NOTE, the projects on these pages are presented in good faith. They may or may not work for you. Any damage to your ICOM IC-705 is not my responsibility as I have no control on what you may or may not do. VK3PE (QRZ.COM for email) Originally created by vk3pe on Jan 26th 2025 Last updated on March 12, 2026
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Bottom relay provides PTT contacts out. 