FT-225RD
My own '225 is for sale. Pse contact me if you want it. Includes Mutek front end and erratic Memory module.
Introduction
Switchable IF filtering Receive IF Split AGC
This was Yaesu's flagship 144MHz radio in 1982. At the time I could neither afford it, nor understand who would buy 25W VHF radio when the same box housed a 100W FT-902DM, HF seemed more exciting then.
If you appreciate analogue and don’t want ‘bells and whistles’ then these can be very reasonable buys. Also remember that old sets don’t date so rapidly, and their frames are built of steel, although the front panel's plastic, and its corners do wear and the knobs are prone to cracking. When something does go wrong there’s a fair chance
that you can repair it yourself. The knobs and buttons are dedicated to one function, there are no menu driven systems here. I find this quicker to use. Yaesu designed a radio that looked good with the 225/101Z/902 series. Contrast the 225 with its successors, the FT-480R, FT-726R and the ugly FT-736R, and you'll see what I mean.
Compare an old radio to an
old car, the speed limit's the same even if the newer model looks more attractive.
If you can live without GPS navigation, air con, electric windows and even
central locking, then you might be content with the older model. This could lead me to another
subject...why are new cars more massive than old ones? Even the old Mercedes
190 looks small these days. I read that slow speed collisions are now more common in car parks, since drivers find it difficult to get in and out of what has become a narrow parking slot! You're offered more gimmicks, but forced to accept
a higher fuel burn, more cost and more emissions. Is there a common
thread here? Newer seems to imply features that the manufacturer can include
easily, although that doesn't necessarily confer better performance. And when the modern electronics fail, it's all over..
In summary, the FT-225 has a single 10.7MHz IF for SSB/AM/CW, and a further 455kHz receive IF for FM. 8.2-9.2MHz VFO. A 13.9MHz crystal x9 provides the 125.1 premix. These feed a PLL which generates 133.3-136.3. There is adequate space on the LO board to insert extra crystals; I'm using the Reverse Repeater shift on 144MHz to select 143MHz to allow listening to the Graves "beacon" on 143.05MHz.
Improvements
The plug-in modules are impossible to work on in situ since each one is surrounded by its own steel 'cage'. I've therefore made up a single sided extender board so that I can bring the board out of the radio but still have it powered up.This has allowed me to work on the front end and exciter boards. The exciter board appears to be double sided, but one side is in fact ground plane only, so a single sided extender board is sufficient. Mic Amp & SSB IF need double sided extender boards.
I removed the 2.4kHz filter from the IF board to
a replacement board that displaced the Repeater
board.
This allowed use of the AUX switch (designed to select alternative LO crystals on Tx when Repeater shift was
enabled) to select between 2.4kHz and 6kHz filters, the latter for AM or "wide SSB". I had an extra
crystal ground for a lower than the standard USB 10.695 BFO. I
left space on the board for a CW filter.. perhaps a home made ladder version
Overall, the exercise wasn't so useful. I've never heard any AM on 2m, and there's no 'HiFi SSB' fraternity on VHF. A normal/narrow/CW option would be preferable. I left space for a third filter on my board, but never could obtain one. There are many more filters available at 9 MHz. Eventually I removed this board, and reverted the modification.
Since the radio has no CW filter, when really needed, I fed an attenuated 10.7MHz IF signal from the IF port [FM board path], out to one of the rear panel phono sockets. This was connected to the FT-707, tuned to 10.7, just outside its nominal 30m band spread.
Default setting is fast The
'slow' setting is too slow, it takes many seconds to back off, and it's worth
shortening both time constants by playing with the capacitor values on the IF
board. With the AUX switch, I can now select AGC OFF by
interrupting the link to these capacitors.
ATTenuator
The Mutek front-end has no attenuator, so the ATT
switch was redundant. I now use it to turn off the power to the
BF-981 Drain. This gives ~30dB attenuation.
Crystal Oven
Kuhne electronic electronic sell a heater QH40A that clips on to
the LO and Counter crystals, and heats them to 40deg.
Split receive
The receive path from the Antenna relay is fed to a BNC on the rear panel. A jumper feeds this back to an N-type socket that is connected directly to the front end board. This permits use of the original antenna socket as a combined TX/RX port, or alternatively a separate receive input is available which avoids the loss in the antenna relay (a PCB type) and the loss at the plug in board, which is far from 50ohm. I
hear significantly better sensitivity by this method.
70MHz Option
4m conversion by modifying LO, Premix, Rx, Exciter and Booster modules.
Transverter Options
The obvious approach is to route the ~1W from the Exciter board out to the rear panel and then when you wish to use the radio as normal, loop back in to the Booster board.
But GW4HBZ had a holistic alternative. He fitted a push button TPDT switch to the rear panel to toggle between Exciter-to-PA or Exciter-via-attenuator-to-rear-panel-BNC. The preset was fitted underside chassis, adjacent to the Exciter pins. A hole has been neatly drilled on the underside cover, to allow adjustment. On TVTR Rx, the path feeds directly to the mixer, presumably his transverters had ample conversion gain. The '225's first Rx stage is off, so there's insignificant cross talk from any 2m antenna connected.
On Tx, the attenuated TVTR signal is so weak that it does no harm to the Rx mixer. With the TVTR button pressed, a few DC volts on tx appears at the BNC to allow switching without a separate wire.
Reference Power levels
LO
chain
PLL output
VFO
125.1MHz -15dBm 133MHz
+2dBm
-14dBm
Sensitivity - The minimum signal that I can copy on the '225 is -156dBm.
S-meter calibration:
s1 -120dBm
s2 -117
s3 -115
s4 -114
s5 -113
s6 -111
s7 -110
s8 -108
s9 -106
s9+10 -101
s9+20 -95
s9+30 -71
s9+40 -42
Sequencer interface
The rear panel five pin DIN socket carried MIC in, a loudspeaker link and
PTT. I used this socket to interrupt the PTT line, and fed it to/from a sequencer
which sat in the amplifier, ensuring that the transceiver went to Tx once all other units had done so.
FIXed crystal channels
I presume that the fixed channel selector was intended to facilitate channelised FM, but I found it very useful to have access to beacon and calling channels at the flick of a switch. Suitable and cheap crystals for the GB3VHF and GB3ANG frequenceis, as well as the CW and SSB calling channels, are available at surplus sales. They also have higher freqs, especially useful if you're transverting to 23cm, to save you having to spin the VFO all the way to 144.8/9 to check those beacons.
Comment
I would have preferred a '225 lite - remove the repeater tone burst board, and repeater shift crystals, remove the FM board, remove the VOX circuitry from the AF board, remove all the varicap diodes from the exciter and front end and their pots on the 'keyer' board. Features that would actually be useful would include a second SSB IF strip, to allow binaural reception through headphones, from both ports of a cross polar antenna, or from two separate antenna arrays during a contest. Other desires include a choice of receiver filter bandwidths, and a transmit speech clipper.
On a different note, the FT-625RD sister radio sold for well over £400 on eBay during
2006, – about the same as it cost new in 1980! The '625 looked very similar to the '225, but had a few
different features – four fixed channel positions rather than eleven, a built
in RF speech processor, a 10.81MHz IF, and no PLL mixer.
For those of you who have no Memory Board, I suggest routing the MEM-in coax plug, (underside) to the rear panel DIN socket, build an external VFO, and power it from the '225. If it's small then maybe bolt it on where the microphone clip can sit. Or make it the same height as the '225, in FV-902 style.There's no need to go for a full 1MHz coverage, ~8.4-8.65MHz is adequate for the DX section of hte band. The front panel offers very useful choices of int/external tx/rx vfo selection.