Antennas for 3.4 GHz

[VK7HH]

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

[VK2XAX]

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

[VK7HH]

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

[VK7HH]

What model antenna Tim?

850 - 6500 MHz or

2100 - 11000 MHz?

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

Hayden

[VK2XAX]

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

[VK2XAX]

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

[VK5ZD]

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

[VK7HH]

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

Hayden

[VK3QI]

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

[VK3ALB]

Hayden,

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

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



Sent from my SM-T350 using Tapatalk

[VK7HH]

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

[VK5ZD]

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.

[VK3QI]

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

[VK3QI]

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

[VK7HH]

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

[VK5ZD]

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.

[VK7HH]

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

Hi Tim,
I wonder how you got on with this and the results you found?

Hayden

[VK2XAX]

Hi Hayden,

Both the wife and I came down with the flue and we're both still trying to get over it!

Between that and work, and an additional time sensitive project, I haven't been able to get back to it

Hopefully soon, since my 3.4GHz transverter has been languishing on the bench,

cheers

Tim

[VK7HH]

Thanks Tim,
My LP antennas arrived the other day so I’ll start to have a play. Interested to see how you mounted the PVC feed arm into the existing metal arm? Can’t quite see in the photo.

Regards
Hayden

[VK2XAX]

The centre mounting point is 25mm square tubing that normally holds the standard feed supplied with the dish.

I've found a piece of exterior electrical conduit is a snug fit for the interior dimensions of the square tube.

Into the end of the conduit is a sawn slot that is a snug fit for the PCB.

My intent is to form a radome out of a water bottle to fit over the PCB to give it some weather protection.

I have some form-able hard line, RG405, to bring back from the PCB to a panel mount N that will sit in a small plate that will be fixed to the back of the dish and then its Heliax all the way down to the shack.


regards

Tim