modifying Ka band LNB for 22 GHz water maser reception

[Eduard Mol]

Hi all,

After the successful detection of methanol masers at 12.2 GHz I was wondering if it would be possible to detect maser lines at other frequencies with my 1 metre dish. Water masers at 22.235 GHz seemed to be a good candidate, because these can be quite strong (several thousand Jy to >10K Jy). Water masers are also variable, which makes them an interesting target for regular observations.

About a year ago I asked in a post on this forum if there are any useful LNBs for this frequency. Unfortunately the inverto Ka band LNBs Wolfgang recommended seemed to be no longer available, so I ordered a triax twin Ka band LNB. It has an LO frequency of 21.2 GHz, and it is intended for receiving at 19.7- 20.2 GHz. It may be possible to receive 22.235 GHz which would be downconverted to 22235-21200=1035 MHz, well within the frequency range of my SDR. Unfortunately, there are two hairpin filters inside the LNB which almost entirely blocks 22.2 GHz. I therefore want to remove/ replace or adjust the filter so I can (hopefully) receive 22 GHz. However, I am far from an expert at this so I am not sure what to do next.

Would it be possible to "re-tune" the filter to 22 GHz?

If not, what could I do to bypass it? Michiel told me that I could just place an isolated copper stripline over the filter, but I am worried that it may cause some unforeseen problems/ losses. It also looks like there is not enough space on the PCB to place a bypass stripline around the filter without removing the filter itself (which is a modification I can not undo)

Best regards,

Eduard

 

[Marcus D Leech]

On my Inverto I was able to see 22.235 GHz without mods. The filters were not very sharp. 

Sent from my iPhone

On May 27, 2021, at 4:18 AM, Eduard Mol <eddiem...@gmail.com> wrote:

Hi all,

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[Eduard Mol]

Hi Marcus, 

I do not have the inverto unit because it was no longer available. I have tested my LNB with a 22. 2 GHz test signal and concluded that this frequency was almost completely blocked. Before that I also did some attempts last winter at detecting the H2O masers in Orion KL and W3(OH), these attempts were unsuccessful.

Op do 27 mei 2021 14:46 schreef Marcus D Leech <patchv...@gmail.com>:

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[Marcus D Leech]

Ah. I had not realized you’d tested. Many of these manufacturers use very similar designs. 

Sent from my iPhone

On May 27, 2021, at 9:30 AM, Eduard Mol <eddiem...@gmail.com> wrote:



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[Captain Anne Flint]

Hi Eduard, 

I would suggest you reconstruct that part of the circuit and play around with it (the filter assembly may be proprietary, but the circuit is not) to see what happens when one cuts traces and/or installs jumper wires. From the photo, I’m assuming you’d need a lower-temperature surface mount soldering iron and a delicate touch on the original assembly. You’re worried that you couldn’t return the filter to its original state and I tend to agree. Things can go really wrong. 

What about Dr. Reeve? he has a lot of circuits online. 

How much did the original assembly cost? Got any older equipment sitting around that could be sacrificed? 

Feet First, 

Wende