What’s It #21 – an RF dummy load

RF dummy load for transmitter testing
RF dummy load for transmitter testing

I’m about to start testing a remote COMM radio. To verify the radio it will need to transmit.

Given these tests, the general convenience of having a transmitter test load, the relative easy of acquiring parts (Amazon.com) & assembly, I decided to build rather than buy.

The design consists of 20 1K ohm 3 watt resistors all in parallel. This total 60 watts at 50 ohms. This is submerged in a quart can of oil to dissipate heat. The effective rating is safely 120 watts and higher loads for short transmission.

The total cost was $12 for one hundred resistors, $7 for five BNC connectors, $1 for each of the quart paint cans, $9 for a 6″x6″ sheet of 20 AWG brass, and $2.75 per quart of light weight motor oil. While the two dummy loads technically cost me $17.75 each, the next two (if I needed them) would only cost me an additional $3.75 each.

What’s It #21 ?

I need two of these and rather than spend $40 – $50 each I decided I’d build them. Here is one.

What is it ?
What is it ?

Garmin understands amateur aircraft builders

For anyone who has worked with Garmin’s prior generation of aircraft avionics, they are all too aware of the challenges of wiring high density D-Sub pin connectors, threading back-shells, and conforming to old standards. So I keep being amazed by the small changes Garmin has made with their latest generation of avionics targeting the amateur home built aircraft community.

I’m very grateful for the switch to standard D-Sub pins and the open top connectors makes the assembly much easier. And here is another example of Garmin thinking like a builder rather than an engineer – mounts which can be switched from the ends to the sides of their new remote mounted radio.

When building a kit plane, everything is up to the builder and this means every airplane is a bit different with hundreds of decisions.

In my RV-8, finding a location for the remote radio was becoming a challenge of compromises. I finally located a suitable space but the radio mounting tabs were in the wrong place to make it work. I was about to concede and build new mounting tabs but when I removed the factory tabs I discovered Garmin had anticipated my need!

With the factory installed mounting tabs at each end of the radio, it can be mounted horizontally or vertically with ease. In my case, the problem was that I needed to mount it across between the RV-8’s forward baggage bulkhead and the Z-brace. Ideally, I wanted those tabs to be on the sides of the radio rather than the ends. Thankfully, Garmin attached the mounting tabs with screws. When I unscrewed the tabs I was delighted to see that Garmin had designed the tabs’ screw locations and the radio’s screw holes (two extra ones hidden under the tabs in their original locations) to rotate 90 degrees and re-attach! All I had to do was unscrew the tabs, turn them 90 degrees and there were nut plates already installed for the alternate orientation.

Garmin had designed the radio to give the builder multiple choices for how to install their radio.

This truly is an example of designing for their end user!

GTR-20 with adjustable mounting rails
GTR-20 with adjustable mounting rails

A 6PDT push button for COMM1/COMM2 radio switching

switch stereo audio, mic, and signals
switch stereo audio, mic, and signals

Traditional aircraft used an audio panel in the avionics stack to handle multiple radios, audio sources, and intercom between the occupant headsets. This was logical when there were so many audio sources which needed to be monitored for different segments of flight – two radios, identifying VORs and NDBs, listening for the outer marker signal, etc.

With the growing availability of GPS for all segments of flight including precision landing, some aircraft have done away with an ADF and even NAV radios. My plane is one of these. There are pros/cons to this configuration but for a lot of domestic flying, it’s safe and complete.

Many newer radios incorporate the intercom and even have alert and auxiliary audio inputs. With all of he capabilities of these modern radios, most of the audio panel capabilities are redundant. The exception is supporting two radios.

Two radios are handy since one radio should always be setup to talk to the airport or to air traffic control. The second radio can handle things like checking weather at the departure or arrival airport. It can also be helpful when you know you will be changing frequencies multiple times in a short period – eg: weather, clearance, ground, tower, then departure control.

Having two radios doesn’t dictate an audio panel. Switching frequencies has become much easier with database integrated radios and EFIS/GPS connected radios. With these systems, a frequency change is often a press of a button.

This leaves the listening to weather and the “convenience cases” when you want to load up clearance and ground to a second radio. The “listen” to the second radio can be handled through an auxiliary input on the primary radio. Now we have only one case to solve – temporarily switching to the second radio.

In a side-by-side airplane, both occupants have access to the panel but in a tandem (or solo) only the pilot can reach the panel. Only the pilot really needs access to both radios. My airplane is a tandem and I fly 99% solo.

A pilot headset has a MIC, a push-to-transmit, mono or L/R headphones, and the ground wire. That’s 5 connections. A switch can handle toggling all 5 wires at once between two radios.

The sixth switch lets us listen to the second radio while connected to the first.

Below a video of the switch. The switch has both solder lugs and PCB pins. The pins can be cut off when using the solder lugs. The push button switch “latches” when pressed and releases when pressed again. It has a mechanical colored indicator that is visible when pressed to the “latched” position.

6PDT Push Button Switch

Stereo farming

soy beans starting to turn

soy beans starting to turn

tomato stakes

tomato stakes

Making a spherical ice "cube" for a unique cocktail presentation

Swanky scotch and whiskey bars spend a fare amount of time (and money) on atmosphere and presentation – how else can they charge $20 for a $4 drink ?!

The glass is only part of the presentation and it’s easy to replicate at home. The ice is another story.

The first task is to create clear ice. There are a number of methods described on the internet and the one that proved successful was directional freezing, detailed by Camper English. I just had to call him out for having such a cool name.

IMG_4674_tuned IMG_4686_tuned IMG_4684_tuned

Using an inexpensive cooler, fill it with nothing more than tap water (or filtered water if your tap water is funky). Put it in the freezer with the top removed or open. Wait about 48 hours. In this time it will freeze down about 4". Remove the cooler from the freezer and let it sit on the counter for about 10 minutes then invert it in your sink and slowly, the block will fall out. It will still have an unfrozen portion. Knock this off to leave you with a block of clear ice. If you want chunks, break off pieces as needed.

To get a sphere of ice, you want to start with a more manageable piece. I tried carefully breaking the block but it was very unreliable and wasteful.

I took six 1-liter bottles and cut off the top and bottom. I drop these into the cooler filled with water before it goes into the freezer. After 48 hours, I remove the cooler as before and let it sit. Then, I break the block apart to free the cylinders. Each piece is about 4" tall as before.

Note: the one pictured has a small amount of front on it because I had tossed it back in the freezer for later use. If you do this, let it sit out for about 10 minutes to temper, otherwise even the temperature of your hand will shock the ice and crack it.

From "cylinder to sphere" you have two options, you can shape it by hand or using a press. Both methods take advantage of thermodynamics.

Hand Method: There are two manual options – melting and chiseling. Here is the chisel method. I tried my hand at the melt method. Using a large stone or thick metal surface, slide the ice cylinder across its face/top. The surface – being at room temperature – melts the ice. It’s a lot like sanding a smooth curve onto the corner of a piece of wood. Turn the cylinder and melt the edges. Keep shifting the ice to round it more and more until you have a sphere.

Press Method: Shell out big bucks, find someone else to shell out big bucks, or try to score a crazy deal on eBay to get an Ice Ball Maker (aka Ice Press). Open the press and insert the cylinder of ice and rest the top back on the ice. The small amount of pressure is now what is doing the work – it’s the mass of aluminum. It starts at room temperature and has a high thermal mass. It melts the ice and its temperature drops. If the chunk of ice is not too big, the excess will melt away as the metal comes in contact with ice. The technique works for shapes other than a sphere. Below is an example video … from Macallan, of course.


I think it’s time for a Gin. Hendricks, perhaps ?