KF5OBS #21:LeCroy WS3162 and HDO4024 Bugs

Exposing some bugs on LeCroy’s new WaveStation 3162 and the HDO4024 oscilloscope.

Bug 1 (WS3162): When modulation is applied to a channel, the amplitude drops below the set value.

Bug 2 (WS3162): Phase control dysfunctional on both channels when modulation is applied to either one channel.

Bug 3 (HDO4024): Spectrum calculation locks up and slows the spectrum update down significantly if “Average” or “Max Hold” mode has been selected previously to switching into “normal” mode. FW: Version: 7.3.0.5 & 7.4.0.5

UPDATE (06/16/2014): Just 15 minutes after I published the video, Dan Payne (Director of Distribution, Teledyne LeCroy) writes this: “Thanks Sebastian – I’ll have the applications team look at it immediately – The video makes it a lot easier to see the application.”

 

Tiger / Rat Tail for Handheld Radios

Handheld radios are getting more and more sophisticated and versatile. The bottleneck for modern handheld radios is often the stock antenna. There is an extremely simple yet very effective add-on called a “Tiger Tail” or “Rat Tail” to remedy this situation. This article is going to explain how to make your own.

For less than $1 in material, you can significantly increase the receive and transmit performance of pretty much any handheld radio. Not just amateur radio, but practically any radio out there, including WiFi routers. The following picture shows a Tiger Tail for a 2m band HT.

Tiger Tail installed on an Alinco DJ-G7

Tiger Tail installed on an Alinco DJ-G7

So if all you need is a bit of wire and a ring terminal, then why bother to write a lengthy article? Well, there are a few caveats and tricks with a Tiger Tail. For instance, some math needs to be done to get the exact wire length just right. Most articles about the Tiger Tail just mention fixed numbers and completely disregard that the amateur radio bands are not the same around the world. They also neglect commercial and low-power (Part 15) applications. And to my surprise, many articles do not even bother to mention that a Tiger Tail is a tuned element. A Tiger Tail that may work perfectly on VHF, may perform pretty bad on UHF. So let’s get started!

The following shows all the tools you will need in some form or another:

Tools needed to make a Tiger Tail for your HT

Tools needed to make a Tiger Tail for your HT

You’ll need a ring-terminal appropriate for your wire diameter, some wire (14 AWG / 1.6 mm), wire strippers, a crimping tool and quite possibly a calculator.

Like I said above, the Tiger Tail is a tuned element and needs to be calculated for the specific frequency range of interest. Since I favor metric over imperial units, let’s start with the formula to use if you like metric:

Length = \frac{30 000}{4 * f} * 1.05

Length = length of Tiger Tail in cm
f = frequency in MHz

What this formula does is calculate a quarter wavelength for the given frequency + 5%. The same formula rearranged for imperial looks like this:

If you would like to calculate the length in inches, simply divide the result by 2.54. Or use the following formula instead:

Len(in) = \frac{30 000}{10.16 * f} * 1.05

Lenn(in) = length of Tiger Tail in inches
f = frequency in MHz

Remember that this Tiger Tail works for a single band ONLY. But there’s a pretty easy trick: if you would like to cover more than one band, like 2m and 70cm at the same time, simply calculate a Tiger Tail for each band individually and connect them to the radio at the same time.

So after you calculate the correct length, simply crimp a ring-terminal on the wire and — just for good luck — isolate the other end with a piece of heatshrink tubing. That’s it, no black magic at all. And this is what the final result should look like:

Ring-terminal crimped onto the end of the wire

Ring-terminal crimped onto the end of the wire

And in case you don’t like to read and you’d like to see some of the math being done for you, here’s a video I made on the same topic. The video also contains a cross-check of the math using a spectrum analyzer:

 

850 MHz Scanner Preamplifier / Filter Project

This article shows how to use off-the-shelf parts to improve the performance of a radio scanner in the 800 – 900 MHz band. Furthermore, it shows how to expand radio coverage by using two different receive antennas at the same time.

For some reason, my new BCD996XT scanner wasn’t working as expected on the statewide digital (APCO 25) radio system. Since this radio system is the primary reason why I got this new scanner, I had to come up with a solution. In addition, I really wanted to expand my receive coverage geographically. This article shows how to improve receive signal strength, greatly increase geographical coverage and reduce out-of-band interference.

So where to start? The obvious. Taking a snapshot of the current situation. I am using a wideband discone antenna mounted on my roof. Since this is a very broadband antenna, I imagined that it was catching a whole lot of signals that I didn’t really care about. A look at the MDO4104B-6′s spectrum display confirmed this.

0 MHz - 1 GHz spectrum without preamplifier

0 MHz – 1 GHz spectrum without preamplifier

The bandwidth is 0 – 1000 MHz (100 MHz / div). Even though the resolution bandwidth is 5 kHz, the MDO4104B-6 was actually pretty fast. But that’s just an aside. You can clearly see the strong broadcast VHF signals on the left. Then there are a lot of signals between 500 and 700 MHz, as well. I have absolutely no interest in signals in that range. And over to the right, you can see — among other things — the desired signals. The control channels for the APCO 25 systems in my area are mostly between 850 and 860 MHz.

Since I am primarily using the BCD996XT scanner for the APCO 25 system, I was willing to filter out anything that’s not in the 800 – 900 MHz range. I realize that I’ll lose the capability to monitor most of the VHF and UHF channels (Aircraft, Amateur Radio, Law Enforcement, Business, etc.) by doing this. But I do have plenty of other analog scanners and I also have 2 more wideband discone antennas laying around. So my decision was made; Optimize the antenna system for 800 – 900 MHz and set up a second scanner (BCT15X) for analog channels.

I also decided to combine the signals of the wideband discone antenna (for local sites) and a commercial 850 MHz Yagi antenna (remote sites).

The two scanner antennas in my yard

The two scanner antennas in my yard

APCO 25 sites are smart in that they actually know what data it needs to relay and what not. If there is no radio logged into the site with a certain talk group, there is no need for this site to relay activity associated with that talk group. So while the discone picks up local sites very strongly, it may be of absolutely no help for communication of a neighboring county if there are no radios of those agencies being used locally. Looking at the map, I realized that there were about 6 remote sites northeast of my house. Perfect for a commercial 850 Mhz Yagi made by Larsen.

So besides filtering, I now had to combine two signals from the two antennas. And I thought while I was at it, I might as well include a preamplifier. For practical reasons, mostly cable loss compensation, it’s always smart to put the preamplifier close to the antenna. I did have a rugged outdoor case laying around. All I had to do is select the right things to put in it.

850 MHz Preamp Box

850 MHz Preamp Box

While looking for a combiner, I found one that actually had a bandpass characteristic for 800 – 920 Mhz. It’s the Mini Circuits ZN2PD-920+ [1]. From Mini Circuits are also the 800-1050 MHz SMA inline filter [2] and the amplifier (ZX60-2534M+) [3]. That’s pretty much everything needed except I did not want to run an extra power line for the amplifier. Therefore, I also ordered two Bias-Tees [4].

Inside the 850 MHz combiner / preamp / filter box

Inside the 850 MHz combiner / preamp / filter box

The wiring is pretty straight forward. The two signals from the antennas are being combined by the combiner, then being amplified by the amplifier and filtered by the bandpass filter. In that order. I was debating to put the bandpass filter in front of the amplifier. After all, amplifiers behave according to the “garbage in, garbage out” principle. Since the combiner had a bandpass characteristic, I did not want to introduce anymore loss.

Close-up of the 850 MHz combiner / preamp / filter set-up

Close-up of the 850 MHz combiner / preamp / filter set-up

I cut a small piece of rigid RF cable in half and soldered two capacitors (100 µF & 100 nF) as well as two wires for the amplifier’s voltage supply on the end. An old power supply for a USB hub supplies the 5 V for the amplifier on the other side of the coax.

The BCD996Xt scanner is very happy with the signal levels

The BCD996Xt scanner is very happy with the signal levels

Immediately after hooking up the scanner, I could tell a great improvement in performance. Not just remote, but also local signals were much clearer and the lock time for the scanner was significantly faster. Beforehand, I often missed the beginning of a transmission. Now I can eavesdrop right from the start. A quick look at the spectrum analyzer confirms that the signal situation increased significantly.

0 MHz - 1 GHz spectrum with preamplifier

0 MHz – 1 GHz spectrum with preamplifier

In case you’re interested in building a similar setup, here are the links to the datasheets of the Mini Circuits products used.

[1] Mini Circuits: ZN2PD-920+, Power Splitter/Combiner, 800 to 920 MHz: http://www.minicircuits.com/pdfs/ZN2PD-920+.pdf
[2] Mini Circuits: VBFZ-925, BPF, 800-1050 MHz: http://www.minicircuits.com/pdfs/VBFZ-925+.pdf
[3] Mini Circuits: ZX60-2534M, Low-noise amplifier: http://www.minicircuits.com/pdfs/ZX60-2534M.pdf
[4] Mini Circuits: ZFBT-4R2G+, Bias-Tee: http://www.minicircuits.com/pdfs/ZFBT-4R2G+.pdf

 

Yaesu FT-8800 Extended TX (MARS/CAPS) Mod

The Yaesu FT-8800 and FT-7900 are very popular radios. For some activities, it may be desired to be able to transmit outside of the amateur radio bands. This article will show how to do this modification with minimum effort at home.

Driving a transverter, participating in the Military Auxiliary Radio System (MARS) or Civil Air Patrol (CAP) are just three examples for which an out-of-band extended transmit modification can be handy. Since “out-of-band extended transmit modification” is awfully long, it’s colloquially referred to as “MARS/CAP Mod”.

The modification procedure is the same for the FT-8800, FT-8800R, FT-7900 and FT-7900R. I will use an FT-8800R to illustrate this article. After this modification is complete, the radios will transmit between 137 MHz – 174 MHz and 420 MHz – 470 MHz.

The mod itself is very easy. It simply consists out of removing a surface mount resistor and power-cycling the radio. The first step is to remove the top cover of the FT-8800. The speaker can be disconnected for more room, but in my case, I didn’t think this was necessary.

FT-8800 with opened cover

FT-8800 with opened cover

The second step is to identify the correct resistor. Be sure to double and triple check that you are removing the correct part. The following picture shows the exact position of the SMD resistor. Click on it to see the super large version.

Jumper location for the FT-8800 extended TX modification.

Jumper location for the FT-8800 extended TX modification.

Once you have identified the resistor, remove it. This can be a bit tricky if you don’t have the right soldering tools. A desoldering tool is certainly helpful, but different people have different ways of performing such tasks. One way is to add a small blob of solder to one side of the part and rely on heat transfer within the tiny part to get both sides loose. Some people just cut the resistor with pliers or a scalpel. The latter option can however damage the PCB and the traces.

After this step is completed, reassemble the radio and apply power. The radio will automatically perform a reset and will be able to transmit.

Startup screen of the FT-8800 indicating that the radio is resetting

Startup screen of the FT-8800 indicating that the radio is resetting