Antennas for 3.4 GHz

[VK7HH]

Hey Tim,
An update.

I removed the feed off a gridpack I had today and replaced it with the LP antenna.
I ran a sweep on 2.4 GHz of just the LP with a short tail (approx 10cm). My directional coupler doesn't cover up to 3.4 GHz.

As you can see, the return loss isn't great... probably something I did.

I then added extra length and mounted at roughly the same focal point as the old 2.4 feed. According to previous posts on here, I mounted it so that the element #12 (13cm) was in the same spot as the previous dipole.

This is the return loss plot mounted on the grid -

Return loss is great down at 2.3 but at 2403 MHz it's only -13dB. Not great but workable.
I then decided to butcher one of my LP antennas and tried to cut the elements a bit shorter to move the frequency up to 2400. After a bit of fiddling i got it close, but not quite. So I got another LP antenna and remounted it and just ran with it as is.

I ran a test on 3.4 and testing against my panel antenna there seems to be a definite improvement. I was hearing VK7ZBX 2 S points stronger than on the panel and it is very directional, unlike the panel. Further experimentation is needed but it's a good start.


Oh... and reading this document -
https://www.wa5vjb.com/references/DesigningPCB-LPs.pdf
says that at 3.4 GHz one of these has burned up at 40W FM. I'm running 20W and with about 10 seconds of key down smoke started appearing out the front of the feed. I haven't opened it up yet to see where, but it seems it can't handle as much power as stated.

Video of the contact/testing coming soon

[VK7HH]

Had a look at the PCB today of the antenna and the resulting burn mark.
Pictured for info:

As you can see it is element #9. As the phase center according to the previous linked document is #6 for 6cm and #12 for 13cm it makes sense that this element is the phase center for 9cm.

Interestingly I had a little bit of hot melt glue near this element on that side of the PCB, not that I think that was a contributor.... but the other side was not burnt at all.

[VK7HH]

Here is the video of the contact testing the LPDA antenna.

[VK7HH]

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

Hi Tim,
Do you have a link to the document with the power test done by W1GHZ? I'm having a look. I can see the info in WA5VJB's document about smoking them at 40W FM, but mine are cooking with just 20W FM. I even tested his 800 MHz to 6 GHz antenna (the larger one) and it too burns up.

Hayden

[VK3QI]

Hatden,

is this what you are looking for?

http://www.w1ghz.org/antbook/conf/WA5VJB_LPA_feed.pdf

Cheers

Peter VK3QI

[VK2XAX]

Oh... and reading this document -
https://www.wa5vjb.com/references/DesigningPCB-LPs.pdf
says that at 3.4 GHz one of these has burned up at 40W FM. I'm running 20W and with about 10 seconds of key down smoke started appearing out the front of the feed. I haven't opened it up yet to see where, but it seems it can't handle as much power as stated.

Yea that's the one, I think I had the W's confused. I've just spent an hour or so looking at all the docs I have and I cant see any mention of a power rating in the W1GHZ docs.

I still haven't done anything yet, other things have been taking precedence.

regards

Tim

[VK7HH]

No worries thanks Tim.
They work fine at 20W on SSB, just FM they get a bit hot.

WA5VJB replied to me and said that he had some running up to 60W SSB into them.

Looking to upgrade to a dish soon

[VK2XAX]

Hi Hayden,

I finally mounted the LPDA on the dish tonight, SWR @ 2403.100MHz is 1.26 and 1.31 @ 3398.100Mhz

see attached pics.

I just need to work out some sort of radome to weather proof the feed so I can stick it on the tower.

cheers

Tim

[VK7HH]

Hi Tim,
Looking good. I received my directional coupler in the mail the other day that will allow me to do readings up to 4.4 GHz now, so I need to place my LPDA in front of the grid and test. I've been testing it in front of a dish.

In other news - I decided to try a Cantenna on the front of my dish. It's just a little 65cm offset Foxtel dish - nothing flash but worth the experiment. I tested the Cantenna by itself and managed to get a return loss of close to 30dB. When mounted in front of the dish I can see dips above and below 3400. I tried trimming and fiddling with the feed, but in the end I settled with what I got which isn't too bad - 20.91dB at 3398.

I need a bigger dish.

[VK7HH]

Further progress on the Cantenna for 3.4 GHz. I did some more measurements and realized my can was too big. I found a slightly smaller can (Big Red Tomato soap - for one!) and mounted a few probes and played around. One immediate thing I noticed was that the return loss curve does not change too much from testing by itself and then mounting on the dish - they are very similar.

I also followed the advice of mounting a small 4mm set screw 180 degrees on the other side of the can. This allowed fine tuning.

I now have managed to get over 33dB of return loss at 3398 MHz - not too bad. There is another dip further up at about 3460, but I'm not worried about that one.

Photos:

[VK2AZ]

Haydan,
For the probe length on your cantenna, did you measure from the inside of the can to the tip or the top of the N inner connector that pokes into the can slightly?

Just playiong with making one at the moment.

Hilary
VK2AZ

[VK7HH]

Hi Hil, I measured from the middle of the N connector to the end of the probe. I ended up having to do a lot of filing as it was way too long first time

[VK2AZ]

Hi Haydan,
Not sure what you mean about " middle of the N connector"?
Do you mean from the end of the little flange that pokes into the can or the inside of the can to the tip?

Hil

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[VK7HH]

Sorry Hil,
Didn’t really describe that properly. From the solderable bit (rear side of the flange).

I figure once the plug has mated on the connector then everything past the tip of the N male is to be included in the antenna

[VK2AZ]

Thank you,
I will give it a go.

Regards

Hil

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