The Elecraft T1 is a stand-alone, miniature antenna tuner unit specially designed for use with low-power HF/6m transceivers. Despite its small size, it uses a built in 9V battery, provides a wide matching range and can handle powers up to 20 watts SSB/CW or 10 watts in FM/AM/digi. It is a very cool general-purpose ATU for mobile and portable use. The T1 is available either ready built or as a kit.
Specs
Network Type .... L-network (series L, shunt C)
C switchable to TX or ANT side
Inductance ...... 0 - 7.5 µH in 128 steps
Capacitance ..... 0 - 1300 pF in 128 steps
Frequency ....... 1.8 - 54 MHz
SWR range ....... 10:1 or better
- reduced on 160 and 6 m
Min pwr ......... 0.5 W, 2-5 W recommended
Max pwr ......... 20 W CW/SSB, 10 W AM/FM/digi
Tuning time ..... 5 sec. for initial tuning
1-2 sec for re-tunes
Display ......... SWR 1:1 to 3:1, PWR 0.5 to 10 W
using 3 LEDs with 5 gradations
Power Supply .... Internal 9V battery
Current Drain ... 20 mA during tuning, 0 mA when idle
Size ............ 11.2 x 6.3 x 2.3 cm
Weight .......... 140 g including battery
Other Features
Besides the specification above, the T1 has some very interesting features worth to mention:
- Power Save: The T1 has been designed with QRP and/or portable use in mind, thus long battery life time is very important. The T1 turns itself OFF after being idle for a few seconds and, since the T1 uses latch relays, the power consumption is really low.
- Good Tuning: The T1 always tries to find the best SWR and does not stop at 1.5:1. Combining 7 inductors with 7 capacitors in 2 network types, the T1 has a total of 32768 possiblities to try. The T1 is very fast, since the best match is usually found within seconds.
- Variable TX Signal: I haven’t tried this yet, but according to the Owner’s Manual the T1 does not necessarily need a constant tuning signal in order to tune. It tunes very well using SSB signal – and you don’t have to whistle 😛
- Remote Control: The T1 has the ability to receive band data from transceiver using a remote cable. Currently, only a ready built cable for the FT-817 is available, but more will probably follow.
- Apealing Look: Despite the small size and compact user interface consisting of two buttons and three LEDs, basic operation of the T1 is piece of cake using the Quick Reference on the front panel. The T1 can tell you both the power, swr and even warn you if is time to replace the 9V battery. Besides these basic indicators, the T1 can also transmit detailed info report on CW by flashing a LED and as a very weak RF signal.
- Open Design, No Secrets: All relevant docs including the schematics are publicly available on the Elecraft web site. This way, you can actually review and evaluate the product before you invest your hard earned money.
Technical Description
The T1 uses 7 inductors and 7 capacitors in an L-network. The capacitance can be placed either at the transmitter or at the antenna end of the network. Each inductor and capacitor has its own DPDT relay, with the individual sections of each relay placed in parallel for reliability. The relays are selected under control of a PIC16F876A microcontroller. The used relays are of latching type and they will not consume any power except when tuning is in progress.
The T1 uses a comprehensive, three-stage tuning algorithm to ensure selection of the best of its 32768 relay combinations. The coarse phase takes the longest time because the impedance is an unknown. Using band data via remote control can, however, reduce this time by eliminating some L and C values based on the operating band. High SWR subtrees of L/C possibilities are also pruned during this phase. Fine and very fine matching stages try successively narrower L/C groups. Once a match has been found, it is saved in EEPROM for later consideration when retuning. A number of such matches are saved, so the tuner will rarely need to tune completely from scratch. If band data is available, it is used to load the last-used network values on each band.
For power and SWR measurements the T1 uses a directional coupler. This type of bridge is inherently balanced over a wide frequency range and requires no adjustment. The bridge outputs are connected to A/D converter inputs on the microcontroller, which then measures the voltages and converts them to SWR or power readings. The conversion algorithm uses averaging and linearization techniques to improve the accuracy of the measurements.
Before matching starts, the T1 determines the peak power of the transmitted signal, then uses a large fraction of this value as a qualifier for SWR readings. In this way, SSB voice as well as any other modulation method can be used for tuning, with little loss of accuracy compared to the use of a constant carrier.
The T1 can also display detailed information about it’s internal configuration (battery voltage, capacitance, inductance, etc.). This info is comunicated to the user using CW by flashing a LED and by transmitting a very weak RF signal. This RF output is generated by placing a digital pulse train on the REF line during “ON” code elements. This modulates the 4-MHz oscillator and its subharmonics, providing audible CW signals throughout the HF and VHF range. The signal is coupled to the transceiver via leakage paths in the SWR bridge and L-C network. Very clever.
Building the Kit
The kit comes with two PCBs, a main board containing most of the tuner components and a much smaller control board containing the control elements like buttons and leds.
The assembly manual is very detailed. So detailed that even people with not much electronics experience can follow it at do it right in the first attempt. On the other hand, because of the pocket-sized design of this device, there is very little space and one must also be very careful when soldering.
The assembly of the main board took me approximately one and a half day including winding the coils. One must keep in mind that this is a pocket size tuner and the space is really tight, so it is a little difficult to solder at many places. You really need a fine-tip (max 1.3 mm) soldering station, although I got by using the one I had which is probably around 1.3-1.5 mm. It is very important to mount the parts in the same order as specified in the assembly guide, otherwise you may find yourself having a hard time. This also applies when winding L1 .. L7. It starts with just a few turns and increases gradually up to 29 turns on L7. I found this to be very, very close to the maximum number of turns there is room for on a T37-2. So it has been very good practice to begin with just 3 close turns for L1, then continue with 5 evenly spaced turns round the core, then 7, 11, 16, 20 and finally 29.
The assembly of the control board didn’t take me more than a few hours but it has not been easy. The space is even tighter here than on the main board and one must pay special attention not to make any mistakes. Removing a part from here looks almost impossible without damaging another one. Fortunately, I did not have to do that.
Special care must also be taken when soldering because no leads or solder fillets may be higher than 1 mm on the bottom side of the board. Otherwise the control board may not fit onto the main board without scraching the MCU. To give you an idea of how small thing are look at this picture:
The picture shows the small control board mounted on the main board. Between the two boards you can see the MCU, which has a normal IC size – just to give you an idea. Anyway, there should be no doubt that if you just follow the very good assembly guide step by step it will work out just fine.
On the Air
User Interface
Due it’s small size, the T1 comes with a very compact user interface and I was very excited to see my reaction. I am by nature very sceptic when it comes to compact user interfaces. I prefer big control panels with big, easily reachable, one-function buttons and knobs and I hate multi-function, multi-purpose, multi-level submenus. For example, the FT-817 can drive me crazy when I want to turn NB and ATT ON and change CW speed; I just can’t do it in less than 30 seconds.
It is, however, different with the T1. The important functions for me are tune, bypass, read swr and read power. All of these are easy to reach and they are also described on the front panel sticker. Even the less frequently needed functions like detailed tuner info and battery voltage are described. Reading the power and swr using the three leds may seem a little funny at first sight. Besides GREEN=1:1, YELLOW=2:1 and RED=3:1 as indicated on the front panel, there are also intermediate values for GREEN+YELLOW=1.5:1 and YELLOW+RED=2.5:1, hi! The same goes for power reading. If one whishes more accurate reading, the Info feature can provide it. Very nice!
Capabilities
The most interesting question is, of course, what can the T1 tune and how fast? I am not interested in matching unrealistic antennas like a rusty nail or a radiator; you can’t make any contacts using them anyway. It is much more interesting to try with some realistic portable antennas:
- MP-1. I adjusted the MP-1 to somewhere in the 40 meter band. The T1 could tune it to 1:1 on every other band, except 80, 30 and 17 meters. On 30 and 17 the SWR was 2:1, while on 80 there was no good match. This was done indoors and the SWR reading was done using the T1 LEDs.
- ATX-1080. No tests yet. The ATX can not support itself as it is and the T1 antenna socket is soldered directly to the pcb, thus too weak to support the antenna.
- Wire Antennas. TBD.
SWR Meter Accuracy
TBD
Remote Control
One very neat feature about the T1 is it’s capability to receive band data from transceivers. As of writing, remote cable is only available for the FT-817, but the communication protocol is fully open and documented, and so one could build a remote cable for his or her own QRP rig. I recall reading somewhere that Elecraft does not whish to provide cables for any non-QRP transceiver. That’s fair, but how about the IC-703? It may also seem a little peculiar, that there is no remote controls capability from Elecrafts own K2 either. On the other hand, there is both internal and external antenna tuner kits in the K2 line.
Anyway, the remote controls capability from the FT-817 works great. When changing band on the FT-817, the T1 will recall the latest good setting for that band. When that is done, the green LED begins to blink for 3 seconds and, if one begins to transmit during this time, the T1 will start to re-tune. Couldn’t be easier.
Miscellaneous Goodies
The developers at Elecraft did really go a long way to take full advantage of having a microcontroller in this kit. Using the Info feature one can obtain detailed information about the full state of the tuner and this includes which coils and capacitors are currently used. Also, using the remote socket one can manually control the relays in the T1. This is very valuable in case of debugging the T1.
Conclusion
Having the T1 in the familly for some weeks now it is really difficult to say anything bad about it. It is a kit, it is fun to build, it works good, it has excelent documentation, it is relatively cheap and it has open design with no secrets (except maybe the firmware).
One should keep in mind that the T1 is intended to be a portable or mobile equipment. This is also obvious from the physical design, since you can easily have it in a back pack or even in your shirt pocket, but it doesn’t really fit into a permanent shack. Surely you can have it lying anywhere, but if you want to see the front panel and access the controls, you will have to make some sort of mount for it.
If you enjoy /P or /M using your home built QRP equipment, then the T1 kit is good for you. If you don’t like building the equipment yourself, you can go for a ready built T1. In any case, the T1 is woth every penny/cent/batka.
References
- Elecraft’s own T1 pages.
- T1 reviews on eHam.net.
- Frequenctly Asked Questions about the T1.
- Local copy of the T1 Documents.