VHF and UHF Crossed Yagi

So I’m wanting to build two antennas. A 2m crossed yagi and a 70cm crossed yagi.

Any tips or tricks out there to put horizontal and vertical elements on the same boom? Would love to have some sort of switch box/relay to switch it from LHCP and RHCP, etc.

I want to build something of quality using aluminum boom, aluminum elements, and I have my own 3D printer. Any advantages / disadvantages of through boom with button insulators or mounting elements on the boom itself with insulators? also spacing between the vertical elements and horizontal elements. Should I do cross or X?

Also, I see all sorts of yagi calculators out there, but only for single polarity? Do I just duplicate it on both horizontal and vertical sides?

Also trying to think about what matching I should use, gamma match, t match, stub, etc.

I’ve never really constructed something this extravagant so any help is appreciated.

Running the elements through a metal (conductive) boom requires you to adjust the element length to correct for changes caused by the boom. Some commercial and plans-on-line designs mount elements on stand-offs so the boom is not in the plane of the elements. Easier than applying correction factors. DK7ZB has a wealth of info and designs on his pages. There may be some examples of this for switchable Horiz/vert polarity or circ. polarization antennas. M2 and HyGain commercial antennas use thru-boom button (insulated) construction and work well but $$… Arrow runs the elements through with no insulation; they work but some dispute if they’d perform better with correction factor changes.

I like the WA5VJB “cheap yagi designs” and have built single-polarization versions for 145 Mhz, 222 MHz, and 435 MHz. . Copies of his articles are available at several locations on-line. Use a non-conductive boom (wood (treat for weather exposure if planning a long-term installation), PVC). I used a length of square wood from the local big box home improvement store. If you can’t find a local source for the elements, try SpeedyMetals online (they also cut to length and are quite accurate). They are very easy to build and match. I’ve seen examples online of people making a circ-polarization version. The DK7ZB designs are higher-performance and a bit more exacting to build.

ARRL and AMSAT books and online resources describe how to get circular polarization. With 2 antennas on same boom, easiest is you offset physically one antenna from the other and feed them with identical length phasing harness lines. These lines have to be selected and built to present the correct 50 ohm impedance at the common feedpoint. There is an AMSAT article on the “WRAPS” rotator and antenna system describing how to do this for a pair of Arrow antennas (2M downlink, includes polarity switching). You could follow the same approach with a set of cheapyagis, it is much easier when receive-only.

I use mostly RH-circ polarized on my 2-way satellite station (M2 Leo Pack). RH-LH switching seems to help, however many folks use fixed RHCP or horiz-polarized yagis successfully (I used a single 5 or 6 element “Cheap Yagi” on 2M before I purchased the LeoPack). Polarity switching RH (default) and LH may sometimes help, but I am unaware of any automated means to determine when to switch. So makes more sense for an attended station.

Cross or X? if you mean orientation of elements with respect to a cross-boom, X is considered better if using a metallic (conductive) boom to keep the elements out of the plane of the boom. Same applies to feedline. Keep it out of the way.

I’d build a single polarization VHF (2M) Cheap Yagi of a reasonable size (4-6 elements) on a wood boom (easier to drill), try it horizontal or vert polarized and see if you like the improvement enough to keep going with the project. You can always use it to hit far-off repeaters or for hilltop roving.

73 de KS1G

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Truely admire the spirit to design and build them yourself!

I considered it but eventually decided to buy the WiMo X-quad antenna for 2m + 70cm as I realized the cost of materials (not to mention the time investment) is hard to beat.

I added the Remote Controlled Polarization Switch so I now have the option to switch Hor-Ver-RHCP-LHCP which suits me well as a HAM radio enthausiast. For SatNogs I leave the antennas in RHCP (which could be accomplished cheaper with the phasing-harness listed on the same WiMo page if that is all you require).

The antennas are up the roof for 2 years now and proved to be very sturdy. Performance (with good pre-amps) is good for SatNOGS and OK for HAM-use. For my station - see picture - it was the right compromise.

Best of luck if you do decide to build yourself, that can be very fulfilling, if you have the time, tools and materials for it!

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How are you bypassing the lna when you transmit when you’re on the ham side of things?

Most LNA that operate with a tranceiver have a relais build in that bypasses the LNA when no power is applied. The power can often be supplied over the coax-cable with a bias-T injector, and/or through a separate line. You apply a voltage during RX and switch off the voltage just before you switch from RX to TX. The LNA is then bypassed and protected. Many tranceivers have a solution to steer this.

Many commercial LNA, like mine also have a VOX-circuit. When they are powered, and detect TX power, they let the relay immediately bypass the LNA to protect its electronics. This can save some switching lines. But beware of limited power handling capability of most VOX-circuits!

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My setup is similar to PA1RB’s: I use a pair of outdoor-rated Advanced Receiver Research (ARR) preamps that include an RF-switched relay rated at 160W. Most of my use is at substantially lower (25W or less) power, so I am well within the ratings. I’m very aware that RF-switching can have reliability issues. Hams running high power levels regularly (tropo, meteor scatter, EME) will often use relays that completely bypass the preamp during transmit, controlled by a sequencer that take the PTT (footswitch or PTT keying signal from WSJT-X or similar) and delays transmitting until all supporting circuits (preamp power, antenna relays, amplifier if any) are ready.

I have not (yet) used my yagis with SATNOGS. I’d have to configure hamlib for my rotor interface, move the serial control connection from my laptop running SATPC32 to the RPi running SATNOGS, and switch the feedline from my transceiver to the SATNOGS SDR. Because the antennas are closer to the ground and are surrounded by trees that are very leafy and wet this time of year, simple omni antennas at roof level suffer less degradation and can outperform the yagis for some observations.

I recommended the WA5VJB yagis to the OP because they are inexpensive and easy to build and I thought he wanted directive antennas requiring steering.