Yaesu Ft 891 Manual Tuners Often#

Yaesu Ft 891 Manual Tuners Often

Had it for almost ten years with no problems.I noticed a weird behavior of my Yaesu FT-891 transceiver. I use a MFJ 974 to tune my ony non-resonant antenna that is fed with balanced feedline. Manual tuners often have more matching range than the autotuners do. A Manual Tuner is a fairly simple device and if something goes wrong it is usually pretty easy to find and fix.

Ultra compact design Measuring 6.1 x 2.0 x 8.6 (155 x 52 x 218 mm), The FT-891 is an innovative Multi-band, Multi-mode Mobile/Portable transceiver with an Ultra Compact and rugged case design.The base of the firmware was started by Chris, M0NKA, and Clint. Yaesu Uncompromising Receiver Circuit Design Ensures.The FT-891 fully supports the ATAS-25 and ATAS-120A Active Tuning Antenna System (optional) allowing for plug and play field and mobile operation. Thermostatically-controlled.

Now the transceiver works as expected - the transmit power is 100W despite the fact that SWR is about 1.5:1.I see two possible explanations. Surprisingly it showed the same SWR 1.5:1 and only 50W of transmit power.Then I decided to disconnect mAT-30 and tune the antenna using only MFJ-971. I bypassed the capacitors and the inductance of MFJ-971 using an alligator clip, which turned the device into just a SWR/power meter. I have a second (manual) tuner MFJ-971, which has a build-in SWR/power meter. I've found a few tables online ( the first one, the second one) that say that SWR 1.5 correspond to only 4% power loss, thus I'm a little surprised.At first I thought this might be some sort of bug in the firmware, thus I decided to re-check the readings using an external analog SWR/power meter. However, if instead of dummy load I connect a real antenna through mAT-30 tuner and enable the tuner by pressing TNR in the transceiver menu, the transmit power (according to MTR) drops to 50W while the SWR is about 1.5:1.

The FT-891 can do that automatically with SOME tuners. Though I'm not familiar with this protocol and thus I don't know whether the tuner could be responsible.Did you ever encounter a similar behavior in other Yaesu products, or products by any other manufacturers? How would you suggest to bypass this limitation and transmit full 100W with my autotuner?Common practice is to tune with low power. Another possibility is that the protocol between the autotuner and the transceiver (over 8pin mini-DIN socket) supports some sort of back pressure ('TRX DE ATU PSE DROP PWR'), and the tuner is one to blame.

My FT-891 can deliver more than 100 Watt with output load 40 Ohm, but that is close to the survival-limit of the power amplifier. In transmitter systems there is no power loss as with mismatched 50 Ohm-intended laboratory systems. And when tuning is succesfull, switch to SSB and adjust the power to 100 Watt or what you need for the QSO.The conversion tables for SWR and loss in dB as found on the internet and in documents are ONLY VALID FOR 50 Ohm source and load systems! An SWR of 1:2 results from 25 Ohm or from 100 Ohm load impedance (or from other complex mismatch). When I try to tune WITHOUT power reduction, I see the message 'high SWR' in the FT-891 and, as already mentioned in the thread, the power fold-back protection is/becomes active.That is rather close to your observation, I think.