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Upgrading the QO-100 setup : adding a line isolator

This page was last updated : 28-Dec-23 12:08:35

As written before the up-converter used in this project is the UpCon6W from Amsat-DL. Recently I found out that they added the text below to page. 

Achtung!
Bitte stellen Sie bei der Inbetriebnahme unbedingt vorher sicher, dass der 2.4 GHz Feed richtig angepasst ist und alle Stecker/Kabel in Ordnung sind. Eine schlechtes SWR und Fehlanpassung der Antenne kann zur dauerhaften Beschädigung und sogar Zerstörung der Endstufe führen!! In diesem Fall können wir keine Garantie übernehmen. Billiger als eine kostenpflichtige Reparatur ist dann vielleicht ein 2.4 GHz ISOLATOR. Bei eBay findet man solche Isolatoren/Zirkulatoren bereits für wenig Geld, zum Beispiel UTE CT3240-OT.

Which I believe wasn't there at the time when Jan PA0JWZ (SK) and I build this project. Translated in English it says:

Danger!
When commissioning, please make sure that the 2.4 GHz feed is correctly adjusted and that all plugs/cables are in order. Poor SWR and antenna mismatch can lead to permanent damage and even destruction of the power amplifier!! In this case we cannot provide any guarantee. A 2.4 GHz ISOLATOR might be cheaper than a paid repair. You can find such isolators/circulators for little money on eBay, for example UTE CT3240-OT.

Although I always take care that the setup is OK, the possibility for a failure is always there (moister, etc). So following the advice I went looking for a Isolator but couldn't find any at the time at eBay and also the Dutch site Marktplaats.nl didn't have any. But when I went digging for more info, I found out that on AliExpress they where selling isolators for various frequency and designed to be used on PCB's (link). Costing  less then 20 Euro I thought it was worth buying one and experiment with it. So I ordered one for the 2400-2500Mhz frequency range and waited for it to get delivered.

After less then 2 weeks a small almost nothing waiting packaged arrived and inside, nicely packed in polystyrene.

The WG2020X Isolator was designed and build at RF-TyT and is basicly a drop in isolator (see : https://www.rf-tyt.com/rf-isolator/drop-in-isolator.html ) which can handle 100 W forward power and 20 W reverse power. Which is more then enough for this project. 

Next thing I had to do was make a PCB to hold the isolator. A small piece of single sided PCB of 30x30mm, 2 SMA PCB connectors, 4 M2.5 bolts with nuts and a little elbow grease  was all it took.  

After cutting the PCB to the correct size, I drilled 4 holes matching the 4 holes in the isolator.  

Marking the exact place where I need to put the SMA edge connectors, I milled away some copper to free the center pin of the connector. 

The 2 edge connectors soldered into place. 

Mounted the isolator to have it connected to the connectors. 

 The pins of the isolator are higher then center pins of the edge connectors so a small piece if silver wire was need to make the connection.

After calibrating my LiteVNA for a frequency span of 2.400 GHz to 2.410 GHz, it was time to see if I got some value for the money I spend and hooked up the isolator.

Marker frequency is the center of the Narrow Band portion of the QO-100 uplink. We see that the S11 is a lottle off the sweet spot, but looking at my PCB construction it isn't a surprise. But a SWR of 1.32 is just 0.1 higher then the specs, is fine by me. And looking at the S21 of -0.14dB I won't complain at all. 

So now it's time to see if the isolator is doing what it's constructed for. 

First we leave the output open (I used a open calibration SMA for it). As a result we see a slight increase of SWR to 1.4 which is quite save for the upconverter.

Next we short the output (I used a short calibration SMA for it). As a result we see a slight decrease of SWR to 1.247 which is also quite save for the upconverter.

Next to be sure, I placed the 50 Ohm calibration SMA on the outpu. As a result we see a slight increase of SWR to 1.326 which is again quite save for the upconverter.

So looking a the above test results, It's save to assume that this isolator will project the finales for the UpCon6W. 

Next step is to box it all up insert it into the output line of the UpCon6W.

But that will be for another day. 

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