1296 minikits preamps

[VK3XDK]

Gday everyone,
I recently purchased a minikits eme179a23 preamp
I needed a bit more gain than my own "versatile preamp" to get over 6db of cable run and i dont yet have any specific 1296LNA designs myself (for EME use)

WOW what a wonderful preamp ( It hears the sparrow fart over in Europe -that's what i tell my 10YO and miss-us about my dish anyway ) -- IT really does perform well, BUT the bl**dy thing keeps taking off!!

I wonder if others have had the stability issues and what has been done to fix it? I'd love to be able to use it!
Looks to me like there may be too much gain for one little box?

Nothing on the website, and yes- my feed has a VERY good return loss. (the LNA even plays up a bit on the bench)
I would email him personally but i feel a bad "Vibe" from past experiences.

[VK4CZ]

Watching with interest... constructed mine a month ago, but am yet to test as I'm now working on the enclosure to go up near the tower.

[VK3XDK]

I probably wouldn't have noticed the instability if it want for my constant sun noise evaluations.

Sun noise here was varying over 2db 10min- to 10min checks (whilst trying to optimize)
at least i know now (back to cascaded pga103's whilst i sort it out)

[VK4GHZ]

I bought one of these MiniKit 23cm preamp kits about 18 months ago, but the general lack of activity ultimately resulted in a complete loss of interest here, and the kit remains, well, as an unassembled kit .

Same with the 150W 23cm PA.
90% finished - 0% interest now.

[VK4REX]

Generally speaking, you will not get high gain preamps operating successfully without some careful placement of absorber material in judicious spots within the case and most likely on the lid. Once the sweat spots are found for the placement of the right type of absorber material they are repeatable for and only for the same case. Change the case and restart the process. For the devices we are trying to use you would normally need to look at spectrum up to 10ghz or more to make sure the devices are stable. I chose to use the G4DDK preamp at 1296 as Sam had put in a lot of work into stability and the finished device worked EXACTLY as specified. I achieved 36dB gain and .25dB noise figure as measured on an 8970B and 5dB ENR noise head and total stability up to 26Ghz. I have tested and aligned several of these preamps for other people and they all performed within normal deviations.

As a side comment, my preamp just let me work Trevor 4AFL at 5x3 over a 78K obstructed path with him using 10mW, lots of good activity happening in Brisbane on 1296 lately.

[VK3XDK]

I dont want to be overly critical with this post,
The preamp is VERY VERY good other than stability and it probably wont take much to fix.
My sun noise calcs/ comparisons are telling my that it is quite a bit better than the 0.5nf that mark is quoting in his specs, i would say more like about 0.4 to 0.45 (which puts it up amonst the very good ones, especially with low pass rejection that it offers))

1296 here (central Melbourne) is very prone to 900mhz? intermod (in which i first suspected) but these preamps really knock it down.

The kit was supplied with some "anti-feedback" foam but is clearly not enough to do the job.

[VK2JDS]

Have a look at the description Sam g4ddk gives for placement of RF absorber material. I run 4 of his lna's here and have some modified vk5eme ones as backups.
I got Sam to send me extra of the correct absorber so the lid and sides of the enclosure near the front end on my home made and modd vk5eme ones got material on them. Cut 1cm lengths half a cm wide and place them either side of the input sma pin.
Another thing i did with a particularly cranky one was to place a 5mm square piece right at the output of the front end device. That shut it up. 6GHz oscilation...

Your qsl card arrived here Graham from our first moonbounce contact
73 Dave

[VK3XDK]

After much messing around and no success, i decided to change the input fet.
All looks %100 now

Very strange but least it now going.

[VK2JDS]

a pic of the absorber material : its not foam, more like the texture of chocolate perhaps.

it must be taking off or doing something wrong when you were using that previous fet Graham.

73 Dave

[VK1KW]

How do you get your preamp isolation? there are no pin diodes. Have cooked a couple trying to get the relays right. I would love to get a proper masthead for 23 and 70 locally.

[VK2JDS]

Hi Rob, no you dont want pin diodes or any others anywhere near the front end. too lossy

How its configured all depends on how you intend operating your station.
For a moonbounce station you would use a septum which already has (i guess) 20dB of isolation depending on the build quality, therefore a 18GHz SMA transco etc will work well.
If using a dipole feed , be it yagi, dish, gridpack etc, then the microwave sma relay will be fine up to modest power levels.
To run a 100 watt amp I would suggest a N transco would be fine, thats what I run on the output of w6pql 150 watt brick when working terrestrial.

sequencing :
If you are using ssb then just key up and dont speak for a second, for cw press the mox key on the radio then start sending(which will give sufficient delay). this works well on EME, even in contests.
For digital modes like JT65 there is already a delay setting built into the software that takes care of the key-up time.

If you really need to idiotproof the station then a vk5eme sequencer is your best bet. have the morse key and handmic ptt going through the sequencer to make sure a random press wont take out the active devices in the LNA.
To date I havent done this here except in the transverters for terrestrial. I have a minikits sequencer earmarked for the EME hut, but so far I have been ok , only about 6 blowups over the years and all repaired using spare fets back in the house on the workbench.
73 Dave