Getting started on 23m EME

[VK2CBD]

Good Dave - I am near Newcastle so I might be further away than you think.

Yep I'll have a look at getting the spetum feed going this weekend - I must talk to my neighbour about that tree...

Cheers and thanks again for all your help

[VK2AMS]

Gday Fellas couldnt resist telling you I had my first EME qso on JT65C this morning with slawek DL6SH best was-23 , the preamp arrangement you suggested was spot on Dave(thanks ) and minikits latest is heaps better that the last one ( I had a small problem with an inferior solder joint on the bias inductor so while i fixed it I put the previous model preamp in and did checks using NFM there was a reduction in sun noise of 3db ) the GS15B amp performed faultlessly with 180W in the shack!it is capable of 300W but I am taking it steady atm.
I will be on tommorrow morning from daybreak as I have a sked arranged with howard G4CCH. As I am well aware having only a 1.8M dish means the "big guns " are doing all the work ! it was interesting learning to track the moon , keep an eye on the doppler constant reajustments etc but it made for an excellent outcome. cheers and good luck to all!
73 . mark VK2AMS

[VK4CDI]

Congrats Mark, always a buzz to get that first QSO in the log........
I will be around in the morning watching with interest, you should have no trouble working Howard.......
Cheers
Phil
VK4CDI

[VK2JDS]

This is Great news Mark, its all working for you and getting the hang of the doppler shift is helped by using wsjt or vk3um's EME2009 program which is well worth a look.

another thing to test using sun noise and NFM ( http://vk1od.net/software/nfm/NFM.pdf ) would be to remove the choke and remeasure noise, as with a small dish you do get a shadowing effect from the choke and its a tradeoff whether the illumination of the dish vs the shadowing of the choke makes an improvement. a good experiment for some day hihi
next is to add a ring of birdwire mesh around the outside to expand it to 2m or more. its very lightweight and just adding 8 inches all around should make quite a difference.

I heard Howard this morning on 090 and he was strong as always on cw but the moon was in trees and he doesnt like my straight keyed morse hihi. You will have no troubles on JT65

Mark what you have proven is that EME is within the reach of anyone with a 1.8 metre dish and I hope we can encourage many others to have a go at this type of exotic 23cm dx!

I will be on air in the morning early
73's de Dave

[VK2CBD]

G'day,

I have now completed a G4DDK VLNA2 kit. The LNA seems to perform to spec in terms of current drawn, circuit voltages and noise power. It is stable with a 50 ohm termination or with an OC on the input. When I connect it to my OK1DFC feed (in a 3m dish) it oscillates. I see this with a spectrum analyser. There is a comb of energy from VHF through to 2+ GHz.

I have tuned the feed with a network analyser (with it installed in the dish) and have roughly 35dB RL on the RX port and 30dB on the TX port. I have the TX port terminated in a 50ohm load when the LNA is connected on the RX port.

This may be a red herring, but I have a second LNA - completely different manuaf, model specs etc, which also ocsillates on this feed, but is happy with an OC or 50ohms

Have anyone seen this sort of problem? Any ideas.

Thanks, Brett VK2CBD

Brett

[VK4CDI]

Hi Brett
Maybe your RL is too! good.......
does it oscillate on both Septum ports?
Maybe its the O/P line playing up?
Isolation relay OK?

Cheers
Phil
VK4CDI

[ZL4PLM]

G'day,

I have now completed a G4DDK VLNA2 kit. The LNA seems to perform to spec in terms of current drawn, circuit voltages and noise power. It is stable with a 50 ohm termination or with an OC on the input. When I connect it to my OK1DFC feed (in a 3m dish) it oscillates. I see this with a spectrum analyser. There is a comb of energy from VHF through to 2+ GHz.

I have tuned the feed with a network analyser (with it installed in the dish) and have roughly 35dB RL on the RX port and 30dB on the TX port. I have the TX port terminated in a 50ohm load when the LNA is connected on the RX port.

This may be a red herring, but I have a second LNA - completely different manuaf, model specs etc, which also ocsillates on this feed, but is happy with an OC or 50ohms

Have anyone seen this sort of problem? Any ideas.

Thanks, Brett VK2CBD

Brett

Brett I assume you have fitted all the microwave absorber material supplied IAW Sam's design & build instructions???

And where did you get the septum? Homebrew?? I assume from OK1DFC design??

rgds

Simon ZL4PLM

[VK2CBD]

Simon/Phil,

yes I have fitted all the absorber material. The feed came from OK1DFC himself. Phil the LNA is connected via an adpator directly to the RX port, so no relay (I have no TX capability yet). I have never had a RL too good before. Actually I did try detuning the RX port, but it still oscillates

Yes it goes beserk on both TX and RX ports. When you say the output line playing up, I can terminate the IP to the LNA in 50ohm and all is good; it's only when it is connected to the septum feed that there's a problem.

I am going to try a short on the LNA input to see whether that will make it osc. Also I'll take the feed out of the dish/change position of the feed in the dish and see whether that changes things. It'd be good to have some RF absorber I could cover the end of feed with.

Brett

[VK4CDI]

Certainly an interesting problem...
When I said O/P line, I guess I was trying to say is it the first or second stage thats oscillating.......
If all else fails, email Sam....

Cheers
Phil

[ZL4PLM]

Simon/Phil,

yes I have fitted all the absorber material. The feed came from OK1DFC himself. Phil the LNA is connected via an adpator directly to the RX port, so no relay (I have no TX capability yet). I have never had a RL too good before. Actually I did try detuning the RX port, but it still oscillates

Yes it goes beserk on both TX and RX ports. When you say the output line playing up, I can terminate the IP to the LNA in 50ohm and all is good; it's only when it is connected to the septum feed that there's a problem.

I am going to try a short on the LNA input to see whether that will make it osc. Also I'll take the feed out of the dish/change position of the feed in the dish and see whether that changes things. It'd be good to have some RF absorber I could cover the end of feed with.

Brett

Brett

did you sweep the Septum at 1296????

I find it surprising that with a 50r load on the LNA its stable but then with the septum it goes mad??

can you post a pic of the setup? pic paints a 1000 words!

Sam is pretty responsive - go ask him ... tell him I sent you LOL

It would suggest the Septum isnt showing 50R or there is some coupling going on

all bizzare

a pic may help

Cheers

Simon

[VK2JDS]

hmmm interesting . none of mine have oscillated or played up at all when you add liberal bits of the absorber material right behind the front end fet and around the inside of the metal box.
pls post up a pic of the inside of your G4DDK, just a 640/480 jpeg etc.
i suggest adding more absorber material on the output side of the front end fet until it shuts up. also the length of the small legs under the front end device is for negative feedback
have a read of Sergei's notes regarding his mods. RW3BP i think, as thats where Sam got his mods from.
go here : http://www.vhfdx.ru/apparatura/rw3bp_12 ... timization
and add lots of material, make yours look like his
also i gather you are seeing this oscillation when the feed is mounted up at the dish focus? dont trust it when its in the shack as it could go nuts
Dave

[VK2CBD]

I have had some success this evening - got more agressive with the input inductor. My gain peak was lower in freq than it should have been, so managed to drag it up by reducing inductance in L1. It is now around 1100MHz.

Now no more oscillations with the spetum feed, however I'd like to know what the NF looks like!

I'll posts some images of the amp and the gain and noise power plots when I get a minute.

I am not sure I am over the line yet, but I think I have made some progress...

[VK2CBD]

I managed to make some quick sun noise measurements this morning with the septum feed and new LNA. I saw 12.5dB sun/cold sky.
Not sure how active the sun is at the moment but this is starting to sound reasonable I think.

[VK4CDI]

Hi Brett
I think Sam reckons a noise peak at 1100Mhz is abt right for low NF.....and your sun noise indicates you are pretty close....
I will be QRV tomorrow morning from 2100Z if yo need a signal....

73
Phil

[VK2CBD]

Here are a few images of the amp etc

I have not posted images to this forum before so heres hoping this works!

Cheers
Brett

[VK2JDS]

from memory i think that gain peak is close to being right, maybe a little higher in freq..
the sun noise rise is good, if you are using the 910 to measure it.
perhaps a bit more absorber material on the output side might help, make it the same as the pic on Sergei's site i linked to before
I will be on air tomorrow morning if you would like a test Brett, just let me know or ring on the mobile
Dave

[VK2CBD]

All,

I am looking for a couple of microwave relays for my 23cm setup. I am conscious of trying to get min insertion loss and sufficent isolation to protect the LNA. Any recommendations - what are you using? Has anyone tried the transco 919 series on EME - these are on Ebay at the moment.

http://www.ebay.com.au/itm/270791420296 ... 1438.l2649

Has anyone measured the ILoss on these at 23cm?

Thanks Brett

[VK2GOM]

I bought one for the Rx switching on my future 23cm EME setup. I also use the same relay for Tx/Rx switching at 10GHz with no problems at all.

I think these relays are rated to 18GHz.

73 - Rob VK2GOM / G0MOH

[VK2JDS]

yes, they work well Brett, I use them here and if you are using a septum there is sufficient isolation to allow quite high power on the transmit port.

[VK2AMS]

Same here Brett I use them on all my transverters as well as the septum polariser, never had a problem with one yet (touch wood)! cheers . mark VK2AMS