2m and 70cms Dual Band Yagis - Why not?

[@ammocraft]

Great to see you back posting. This is the goto channel for antenna modelling.

[@hamradioguy-g0ksc96]

thank you

[@pribeiro]

Glad to see you active and ok. Regards.

[@hamradioguy-g0ksc96]

Thank you

[@andreivincene4785]

Great video and explaining! Thank you!

[@heinzschopf9118]

Very interesting insights of the combination problems which can occur. Even the harmonic infeed problem with risk of destroying the RX stage is rather frightening.

[@hamradioguy-g0ksc96]

Thanks Heinz, As I mentioned in the video, these are worst case scenarios although all or any of these issues can occur, the worst being the twin-fed problems to the RX of the primary band. It is better to know what could happen to take measure to prevent it or use this information to guide your antenna decisions differently.

[@heinzschopf9118]

​@@hamradioguy-g0ksc96 TNX Justin for your reply! My actual setup is rooftop mounted an I0JXX 6m 7el Yagi (12 m above ground, 2 m above roof) on the lower and a 2M12 on the upper mast position, with a distance of roughly 2m. M² does a great job here since over 2 decades, Italy antenna performs also well but is mechanical crap (round boom with weak element fixation)... Now i write down what i am thinking about since 2 or more years, all your antenna concepts (as well as the others) in mind...: Since it is not a problem to "hide" an 11m boom where there is already 9,6m mounted, i would like to build myself two boom systems with 11m sqare tapered or so, eventual self supporting w/o ropes, carrying mixed antenna systems. I could imagine for the lower boom a mix of roughly 9el@6m, 5el@0m, and something 20el@70cm. 10m centered around the mast tube. Maybe the 70cm elements would better go on the boom downside. So the longer elements to have some free sight for them. 70cm hanging below with some distance blocks and 6m + 10m on top of the boom. I think these bands should not interfere and they could even be carried out with three coax feedlines seperately. Then the upper boom should carry about 13el @2m and maybe 6el@4m. Also 2-cable solution . 4m centered around the mast tube. Also no interference to be expected between 2m and 4m. What is your opinion all about? Risk of RX destruction abolished? Is it possible to create such a concept on EZNEC, or do you see any obstacles? 73 de Heinz, DL2RDT

[@hamradioguy-g0ksc96]

@@heinzschopf9118 it is a difficult one, you ideally need those with a third harmonic relationship with the biggest distances between them, 2m and 70cms, 2m and 6m and so on. 'ideal' stacking distances are not just frequency dependant, the lengths of the associated booms play a role too - the longer the booms, the wider the spacing needs to be. The mean height of the 70cms is going to be greatest (in terms of wave lengths) so mechanical issues aside, I would place the 70cms first above the rotator, then 6m then 2m at the top with widest spacing possible between each. calculate the distance you have in wavelengths rather than just metres.

[@hedgerowpete]

A great video. A genius level explanation, you need to be university level understandings to get the information given. I was hoping that you could explain it in English.

[@chazwozza67]

I use a dual band 2/70 yagi never had a problem with it

[@hamradioguy-g0ksc96]

If you are happy with it, that's great!

[@medaturbo9899]

Thank you

[@AndreasSpiess]

Same question as Randy: What about the Arrow where 70cm and 2m have different polarization? The same problems?

[@hamradioguy-g0ksc96]

no, not when in opposing planes and assuming the elements are perfectly centred. If the elements are off set to one another then there will be some distortion. worst on 70cms as a result of the offset effectively being 3 times that of 2m (in terms of frequency)

[@stephenpadley6684]

Hi, I've got the Arrow 2, if you run the single 2 mtr only what power can you run output. Says max 150 watts and only 10watts duel. What would you advise.

[@nickmoniker]

I would be interested to see what would happen if the two antennas were cross-polarized,

[@hamradioguy-g0ksc96]

Ni issue when in opposing planes and assuming the elements are perfectly centred. If the elements are off set to one another then there will be some distortion. worst on 70cms as a result of the offset effectively being 3 times that of 2m (in terms of frequency)

[@eoinm0nvk110]

Currently building a moxon 20m, I am using 4 glass fibre poles with the wires inside, so there is a bend towards driven / reflector at the ends. I have only just found your videos, great Ty. How would you model the bends in EZNEC?

[@hamradioguy-g0ksc96]

difficult to do accurately without NEC4.2 running on EZNEC

[@georgejaroslavsky5148]

Excellent explanation. And what about the 2m/70cm interaction if instead of a dual band yagi we try a Cubex like approach (Kingbee cubical quad)? (Jorge, M0LDW - LW5DX)

[@hamradioguy-g0ksc96]

there is still a third harmonic relationship regardless of element overall size. Justin

[@43WR155]

Thank you