Installing a SANDIA STX 165 Transponder/Encoder

//Installing a SANDIA STX 165 Transponder/Encoder

Installing a SANDIA STX 165 Transponder/Encoder

I recently bought another Stearman, my third. It’s a beautiful Scott White rebuild, and I bought it from Bill Nice and his partner in the plane, Scott Ackerson. Fine gentlemen, and a gorgeous airplane. The whole process of acquiring the plane and getting it home from Indiana to Minnesota during some of the worst Spring weather in recorded history should probably be the subject of another article, but suffice it to say it’s now home, and I once again smile like a little boy when I open the hangar door.

This is a piece about the transponder I installed as soon as I got the plane home. My home field, Faribault, Minnesota (FBL), lies just several miles south of the edge of the Class B airspace for MSP. Of course, in order to legally fly under the “wedding cake,” I need an altitude reporting transponder, meaning that without one I cannot fly more than 3 miles north of my home airport, and one of the only shortfalls this particular airplane had was the absence of a transponder. So I went transponder shopping.

The last time I put one of those in a Stearman, you had to have a transponder, paired with an encoder, which mounted as separate unit. That meant finding two separate mounting locations, lots more wires and an extra circuit breaker. Putzy. I soon discovered that there are now units available that incorporate the transponder and encoder in one small box. The one I soon settled on was 165. It’s small (1.78” x 3.5” x 7.34”), light weight (1.3 lb.), and draws less than an amp. They even offer an optional adapter for mounting it in a 3 1/8” panel hole, which I did not need since I had a radio side panel in the back cockpit. I called and talked to Dennis at SANDIA for about a half hour. The more we talked, the better it sounded, but once he told me about the “Old Man Mode” that enables you to switch the displayed code to huge numbers that even my 65 year old eyes can focus on without my reading glasses, I was sold. One phone call to Gulf Coast Avionics with my credit card in hand, and a new unit was on its way.

STX 165 box contents #1

Fig. 1 STX 165 box contents #1

Fig.2 - STX 165 box contents #2

Fig.2 – STX 165 box contents #2

The box arrived several days later, and I excitedly opened it. I’ve attached two photos of the contents. The box included the STX 165 unit, and several bags of needed connectors. The Gulf Coast guys warned me that an antenna was NOT included, nor was antenna cable, since those items will vary so much from installation to installation, so I ordered an antenna, which was shipped along with the unit. I had previously arranged for my friend, Craig, to help me install it (I’m an A&P, but he’s a retired airline radio mechanic and has forgotten more about avionics installations than I’ll ever know…). He told me not to order any antenna cable, as he has a huge supply of it. I was surprised to note that installation instructions were not included in the box, but there was a little note that explained that SANDIA makes those available online (http://www., and you can print them from there. Likewise way they don’t have to worry about issuing revisions, they just tell you to download and print the instructions as close to installation as you can, and that way you will always have the most current instructions available. Not a bad plan, but it assumes an installer will have a computer and printer handy. On the other hand, this allows a prospective purchaser to go to the website for SANDIA and check out the instructions before even ordering the unit.

The other thing required but not included was a 1 amp circuit breaker, which the installation manual specifically calls for to protect the transponder. So, I ordered one of those too. Once all the parts were here, we met in my heated hangar on a rainy cold day and went to work. Actually, I should say HE went to work, as there’s only room for one in that back cockpit, so I just handed him tools and parts as he worked his magic.

Fig.3 - STX 165 Box before installation

Fig.3 – STX 165 Box before installation

We decided on locating the unit at the aft end of the existing radio panel. Craig said he could do everything without removing the radio side panel, so he did just that. He put drop cloths in place to catch the refuse that results from all the nibbling, filing, and drilling, which worked like a charm. He located power and grounding sources, and routed wires as necessary. He had to relocate a couple of switches and headset plugs. In a couple of days, it all came together, and powered up just fine. See the attached photos for before and after shots of the panel. Looks great!

Fig.4 - STX 165 Box after installation

Fig.4 – STX 165 Box after installation

Then we did a log entry and 337 for the installation, revisions to the Weight and Balance Report and Equipment List, and it was time to make it all legal with the VFR transponder check. As soon as I could get an appointment, I flew the plane to MKT, where Jason at North Star Avionics did the check and made the log entry. I flew home with the transponder on in ALT mode, knowing I was quietly blinking away on some distant radar screen somewhere miles away. I also knew I could now legally fly under the MSP Class B airspace to waggle my wings over my house!

In conclusion, I would recommend this unit. One must remember that the kit doesn’t include antenna, cable, or circuit breaker, so you’ll have to do something to fill those squares. You’ll end up with a unit that doesn’t take up much space, is easy to install, and best of all can display big numbers for old guys like me!

By |2016-11-13T09:33:13+00:00November 12th, 2013|Flying-Wire|Comments Off on Installing a SANDIA STX 165 Transponder/Encoder

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