Antennas for 3.4 GHz

23cm, 2.4/3.4/5.7/10/24/47 GHz and above - antennas, propagation, operating, etc. Includes Optical communications, with light,
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Antennas for 3.4 GHz

Post by VK7HH » Mon Aug 05, 2019 11:46 am

Hi All,
I want to get a slightly better antenna with more gain on 3.4 GHz than my GARC panel that I currently have.

As I'm relatively new, I wonder what others have done? I've seen coffee can feeds etc.. but I don't have a dish just yet (still looking for one).

Perhaps I can modify a gridpack antenna, shorten the dipole. Will the focal point change?
Any other antennas that can easily be converted to 3.4 GHz?

Hayden

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Re: Antennas for 3.4 GHz

Post by VK2XAX » Mon Aug 05, 2019 12:20 pm

Hi Hayden,

I'm in a similar situation so I decided to change out the feed of a 2.4GHZ grid pack for a WA5VJB LPDA. This gives me a dual band antenna for both 2.4 & 3.4 GHz.

The PCB LPDA's handle up to 60w before starting to cook. There's a doc on the net from W1GHZ who did that test Smile

My grid pack is 20dBi on 2.4Ghz and should be similar on 3.4Ghz given the 3.4GHz feed point is not at focus.

I just need to add the coax and N connector and I'm done. I'll post test results when I've finished it.

cheers

Tim
GridPackmodfor3.4GHz.JPG
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Re: Antennas for 3.4 GHz

Post by VK7HH » Mon Aug 05, 2019 1:18 pm

Awesome Tim, be interested to know your results.

Is it possible to get the LPDA at the correct focal point? I have a spare conifer dish sitting at home

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Re: Antennas for 3.4 GHz

Post by VK7HH » Mon Aug 05, 2019 1:30 pm

What model antenna Tim?

850 - 6500 MHz or

2100 - 11000 MHz?

https://www.wa5vjb.com/products1.html

Hayden

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Re: Antennas for 3.4 GHz

Post by VK2XAX » Mon Aug 05, 2019 1:53 pm

VK7HH wrote:
Mon Aug 05, 2019 1:18 pm
Awesome Tim, be interested to know your results.

Is it possible to get the LPDA at the correct focal point? I have a spare conifer dish sitting at home
I used the previous 2.4GHz feed as the model for positioning so that the 2.4GHz feed was at focus, this puts the 3.4GHz feed slightly out of focus. Given the dish is 20dBi@2.4GHz, math tells me that , if I focused it on 3.4GHz, it would be about 26dBi.

Given the 3.4GHz feed is slightly out of focus I'd expect some attenuation so I'd expect the gain to be somewhere between 20 and 26dBi on 3.4GHz.

regards

Tim
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Re: Antennas for 3.4 GHz

Post by VK2XAX » Mon Aug 05, 2019 1:57 pm

VK7HH wrote:
Mon Aug 05, 2019 1:30 pm
What model antenna Tim?

850 - 6500 MHz or

2100 - 11000 MHz?

https://www.wa5vjb.com/products1.html

Hayden
The 2100 - 11000 MHz unit.

I bought a few of them to experiment with sometime ago.

TT
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Re: Antennas for 3.4 GHz

Post by VK5ZD » Tue Aug 06, 2019 11:08 am

Replace the original 2.4GHz feed with one of these.
I've made 2 of them for 3.4GHz and they work well.

IMG_20180731_235823.jpg
IMG_20180731_235837.jpg
73
Iain Crawford - VK5ZD
Munno Para West, SA - PF95ih

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Re: Antennas for 3.4 GHz

Post by VK7HH » Tue Aug 06, 2019 11:24 am

Thanks Iain,
Looks good, do you have any more info on the construction of the bi-quad?

Hayden

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Re: Antennas for 3.4 GHz

Post by VK3QI » Tue Aug 06, 2019 3:33 pm

Iain,

In your picture of the bi-quad, shouldn't the parabolic reflector be turned 90 degrees to have the bars horizontal?

Or is the bi-quad orientation incorrect?

Cheers

Peter VK3QI

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Re: Antennas for 3.4 GHz

Post by VK3ALB » Tue Aug 06, 2019 9:34 pm

Hayden,

I've used templates from this site. Works for me on 1296 and 2403.

https://buildyourownantenna.blogspot.co ... lcome.html



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Lou - VK3ALB

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Re: Antennas for 3.4 GHz

Post by VK7HH » Tue Aug 06, 2019 9:37 pm

Thanks Lou, that's an interesting looking site. I'll check it out!

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Re: Antennas for 3.4 GHz

Post by VK5ZD » Wed Aug 07, 2019 12:05 am

VK3QI wrote:
Tue Aug 06, 2019 3:33 pm
In your picture of the bi-quad, shouldn't the parabolic reflector be turned 90 degrees to have the bars horizontal?

Or is the bi-quad orientation incorrect?
The bi-quad orientation is correct. It was just convenient to clamp the antenna on it's side in a bench vice to take the photo.
73
Iain Crawford - VK5ZD
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Re: Antennas for 3.4 GHz

Post by VK3QI » Wed Aug 07, 2019 1:24 am

Iain,

A bit of a Dorothy Dixer.

Many hams think that the bi-quad should be horizontal for horizontal polarisation, when in fact polarisation is at 90 degrees to the bi-quads.

Hayden had earlier questioned as to whether the 2.4 Ghz grid would be too wide for 3.4GHz. - the main thing is to get the grid horizontal - I have seen people add extra mesh (such as brass flywire) but there is little improvement. A different story at 5.7GHz though.

Cheers

Peter VK3QI

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Re: Antennas for 3.4 GHz

Post by VK3QI » Wed Aug 07, 2019 1:34 am

Hayden,

You asked about the position of the focal point.

If you go with the LP style of antenna, then the following reference is well worth studying.

https://www.wa5vjb.com/references/DesigningPCB-LPs.pdf

The section on phase centre will determine the position of the LP.

Generally, you place the LP so that the phase centre of the highest required frequency is at the focus and accept theslight reduction in gain at lower frequencies.

Cheers

Peter VK3QI

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Re: Antennas for 3.4 GHz

Post by VK7HH » Wed Aug 07, 2019 8:08 am

Thanks for that link Peter. I have ordered a few of those log periodic antennas. I wanted a couple for testing anyway. I'll have a play with the grid and post my results here.

Keep the ideas coming though. It seems the grid pack modification is probably going to be easiest for me.

Regards
Hayden

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Re: Antennas for 3.4 GHz

Post by VK5ZD » Wed Aug 07, 2019 4:09 pm

OK. Just for clarification, both the photos in my previous post were taken with the antenna on it's side.
In normal use, the grid bars are horizontal and the biquad feed is vertical.
There is nothing to be gained by adding mesh for use at 3.4GHz.
The link posted by Lou will give the required dimensions.
Mine was actually built by scaling a 2.4GHz design I found online.
After construction, I adjusted for best SWR (i.e. least reflected power) by sliding the reflector plate on the boom.
It was soldered in place when the best position was found.
73
Iain Crawford - VK5ZD
Munno Para West, SA - PF95ih

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