GW4RWR - Yaesu FT-707



†So what's special about this old horse? Nothing, actually. But it does offer the few features I need, including a 600Hz 8.9 MHz IF filter. Itís quite compact, although it does weigh over 60N. The bar-graph LED meter is great for monitoring relative power out, being fast to respond to voice peaks, but it is a bit lame as a receive S-meter. I see that Yaesu reverted to a traditional moving coil meter in the successor FT-77 radio.

Two things about this radio annoy me. Firstly, the VFO mechanism. Is mine unique in having developed some backlash? I admit that I've been spinning that knob to check the beacons and search for activity since 1984. I now get 100Hz slippage every rotation of the VFO knob. Secondly, the receiver goes to pieces on 40m and 80m. The front end mosfet has to be by-passed or attenuated, and I suggest that the MARKer switch be redeployed for this, otherwise these lower bands are unusable with full size antennas. Perhaps the radio was designed for short mobile antennas, where this shortcoming is not apparent. Please email me with your own findings.

I owned the Scanning VFO Memory, FV-707DM, for a few months. It had eleven memories, and could split tx/rx between it and the analogue VFO. I don't recommend its purchase, it's a gimmick. The analogue VFO frequency cannot be dumped into the FV-707. It can only be tuned using the up/down buttons. Itís noisier than the analogue VFO, and funky chirping noises are heard as frequency is changed. The 100Hz step change was too coarse in my opinion. Rather make yourself an analogue external VFO,  the rear panel has an accessory DIN socket to support external VFOs. Inserting a DIN plug will switch the internal VFO out of circuit, the required VFO can then be selected by putting a few volts on the right pin of the ACC socket. Here's a suitable VFO circuit with switching between the FT-707's internal and external VFOs.

G3TSO published mods to include the 1.8MHz band, mimicking the FT-107 circuitry, and I recall that 'Amateur Radio'(?) magazine published a mod to receive 50MHz, with 1mW available on transmit. It used one of the existing LO crystals, but took the image product, so that the VFO would tune 'the wrong way round'.

If you're feeling particularly in need of a challenge, how about an FT-707 on 70MHz ? This would require a 84.4MHz local oscillator, with 'high side' mixing. Pre-mix becomes 84.4 - 5.3 (vfo) = 79.1 , and output RF = 79.1 - 8.9 = 70.2 MHz.
Note that the VFO tunes 5-5.5MHz, where the lower vfo frequency translates to the radio operating at the top end of each 500kHz band. I admit that filtering out the 87.8-88.1 image may be a problem in some areas. 88.1MHz (imaged to 70.3MHz) is used for BBC Radio 2 from Sandale (250kW) for SW Scotland, and from North Hessary Tor (160kW) for Devon. This is the method used by the '707 on HF, so it would be interesting to establish if the digital display could be made to work. Alternatively, a local oscillator on 66.6MHz, with 'low side' mixing, would maintain the VFO dial tuning in the correct sense, but would invert the sidebands. This method puts the image on a more practical 52.2-52.7MHz.









This is the accompanying transverter, and its physical construction is excellent. One RF band module can be plugged in at a time, and the module requires 1mW of drive for up to 10W of output. Note that the FT-707 transverter output is tapped off from the feed to the PA board. Thereís sufficient drive available here if the resistor values just behind the phono socket low-level-out on the FT-707 are altered.

Interfacing of the FTV-707 with the FT-707 is amazingly straightforward. The HF antenna is now connected to the transverter rather than the transceiver. DC power from the power supply is connected to the FTV-707, and an integral lead then feeds that power on to the FT-707. Four pin connectors are employed, and one pin is reserved to carry a low current DC-on-TX signal from the FT-707 to switch the FTV-707 to TX. If the transverter is switched on, then that DC signal is not fed back to the transceiver's PA, preventing it from ever transmitting into the receive converter. Whilst the transverter is switched on, relays within it bypass the HF antenna, and the downconverted VHF signal is passed back to the FT-707's antenna socket.

Conversely, with the FTV-707 switched off, the DC-on-TX signal from the transceiver is looped back to its PA, enabling full power on HF, and the HF antenna is brought back into circuit. This obviates all the hassle normally associated with using a transverter, and similar principles are used in Yaesu's FTV-107 and FTV-902.

You could conceivably run two FTV in parallel, transmitting on two bands simultaneously, and switching between either receive converter to listen for replies.  A more elaborate extension of this idea would be to use a second 28MHz receiver, affording simultaneous dual band transmission, and receiving audio from the separate radios through the left and right ears of a stereo headset. Good for multiband, such as the RSGB Christmas Cumulatives, when you want to work as many bands as possible, during a two hour window? This would be similar to military Air Traffic Controllers, who routinely make simultaneous transmission on VHF (civil) and UHF (mil), such that the pilot hears all the controller's transmissions, but canít hear pilots on the other band.

The frame includes an 'external' button, which bypasses the receive converter, connecting the HF antenna instead. I've used this facility to connect my Meon 50MHz up as a receive converter, and switch between 50MHz and 70MHz quite quickly. GB3BUX can be compared on its 50.000 and 70.000 frequencies very easily in this manner, and cross banding is made quite straightforward. Very conveniently, when the transverter is off, the HF PA is enabled, so thereís no antenna cable switching required, or danger of inadvertently transmitting 100W into the receive converter.

Within the frame, a shielded box houses an ALC module,consisting of one bipolar stage which throttles the drive to the RF module. Yaesu should have taken the ALC from the RF module output, and fed it back to the FT-707 IF board, rather than to this down-stream limiter. The FT-707 low level output gets dirty when the Carrier/Mic Gain pot is advanced beyond the twelve o' clock position, and no amount of action by the ALC in the FTV frame is going to clean this up. When using my home made transverter, I feed a sample of its fwd/rev voltage back to the FT-707 ALC on the IF board, via the rear panel accessory DIN socket. This is simpler and more effective. Yaesu could have routed the ALC back to the FT-707 by superimposing its negative DC signal on the transverter RF tx line. The transceiverís meter can now be used to show ALC action ALC, otherwise its LEDs shows nothing during transvert TX.

Other front panel controls include pots marked 'Tune' which peaks the transmit side using varicaps. This is pretty redundant on the limited UK 6m, 2m, 70cm allocations. To the right, the 'Band' switch selects the respective LO crystal for each two MHz band section. A 'Shift' button can select two possible additional crystals for use on TX. Presumably this was meant for repeaters, although the FT-707 was never designed with an FM facility! The right-most pot controls the RF gain to the front end 3SK51. A tidier design would have included a link back from the FT-707's AGC line to the transverter, not left it to be controlled by hand. It's clear that the transverter was an afterthought to the original HF transceiver. So, plenty of spare front panel switches and pots if you wish to try some ideas. I hacked a 2m module to work on 4m. The PA 'brick' had to be discarded, although in retrospect, in the spirit of Living Beneath One's Means, I should perhaps have sawed it open to see if it could have been retuned. A 2N6082 stage built on to the original heatsink.  Another 2m module remained untouched. A pity that the transverter frame wasn't large enough to house more than one module; I understand that three can be fitted in the FTV-901 and FTV-107.  All these plug in RF modules are of obsolescent receive design - 3SK51 front end and 3SK51 mixer. There is plenty of space to change these, however, if you want to muck about with more modern devices and mixers, although the limiting factor for most users will be the 3SK73GR front end in their FT-707.

That 4m transverter has since been sold on eBay to a Greek amateur for a staggering £159.



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Surprisingly popular on the second hand market, this antenna tuner is fitted into an identical frame to that used in the transverter.  Inside there's a T-network, a relay switched dummy load using 8V feed from the FT-707, and an illuminated Power / SWR meter.  200W or 20W fsd.  Don't try to tune any balanced feeders with this tuner, it's designed to improve the matching to unbalanced feeders. But let's face it, if your antenna's properly tuned, you don't need an ATU. Perhaps it's useful for mobile installations.  Quite a useful power meter, at least.



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