Introduction to tuners and tuning
Arv K7HKL suggests the type of antenna tuner depends on the type of antenna:
- L-network for end-fed or high impedance antennas.
- T-network for medium to low impedance antenna.
- Pi-network for dipoles.
He suggests it is unfortunate that specifications for ATU’s usually do not include the adjustable impedance range for each band that they cover.
Bill Schmidt K9HZ suggests there is a false supposition here that you must tune under full power. It is considered a good design to tune with just the amount of power needed in order to tune… not full power. This can very easily be implemented on the uBITx with a relay that substitutes in a “Tune RV1” set for a much loser tune power.
List members suggested options for simple external antenna tuners for the µBITx transceiver. The list of potential tuners below (organised by type) is not intended to be exhaustive, but illustrative of the choices available.
The LDG Z-100Plus tunes with only 100mW of power. It holds eight AA batteries internally, making it ideal for portable QRP operation. Small, light weight and self-powered.
However, Rahul VU3WJM found that the match at low power levels was inconsistent. He had to reduce the resistors in the ADC sample line for QRP operation.
From the marketing description, this unit handles up to 125 watts SSB or CW but requires only 0.1 watts to tune, making it ideal for QRP operation.
Mike WA1MAD has built the Sota beam Mountain tuner. He says, “It is easy to build, but very manual and only covers 40-17.”
Dave K8WPE likes the Emtech ZM-2 better as it has air variable capacitors whereas the 4SQRP uses poly variables.
Dave K8WPE prefers a small Z match like the Emtec, 4SQRP tuner, GQRP tuner, etc. At the home QTH, Dave uses an MFJ 300 watt roller inductor tuner.
He says that the reason he likes manual tuners is he can look at the numbers on the dials and if they are different from what he usually sees he knows he has antenna troubles, i.e. an antenna down, ice coated, wrong antenna, a short somewhere. With the automatic tuner it just tunes and you don’t know if its the antenna or the tuner that is making your transceiver happy. And even at 5 watts or less we can fry an IRF510.
Allison KB1GMX suggests the ZM-2, 4Sqrp, SLT, and L-tuner all work. The 4sqrp, L-tuner, SLT, and Elecraft T1 are in use in Allison’s QRP rigs for power up to 10W. For higher power a home-built L-tuner easily takes 100W. Those get used for the inverted L and the 160M Inverted V as all the other antennas are 50 ohm resonant removing losses though a tuner and coax.
Allison says, “By far the best antenna is a matched one. Second best is any needing a tuner.”