Conversion of the Yaesu FT-221R from 144 MHz to 70 MHz

By Geoffrey GI0GDP, 14 June 2008

Preamble

This revolves around being able to change the translation PLL from an injection frequency of circa 134.4 to 59.5 MHz for a 10.7 MHz IF without a total rebuild.

This can be done if the VCO is let run at twice the needed injection ftrequency of say 119 MHz, which is only 15.4 MHz below normal in the 2 metre version. Dividing the final VCO by 2 has the effect of band spreading the VFO dial so that each division of the dial is 500 Hz as opposed to the previous 1 kHz. This also means that two new local crystals are needed to cover the 4 metre band 70.000 to 70.475 MHz. But if you are going to use it for CW/SSB then only the lower crystal is needed.

Board Modifications

You will need to get a hold of an extender board or make one from a 0.156" edge connector and a 100x80mm piece of PCB, I didn't use a double sided PCB.

This is the list of boards to be modified and some don't need much changing however others do, keep all the bits because someday you may wish to go back to the 2 metre band.

1. The RX RF board PB-1456
2. The TX Exciter board PB-1466
3. The Booster or PA board PB-1470
4. The Local board PB 1454
5. The PLL board PB 1455
6. Can’t think of anymore.

The RX board PB-1456

Only needs the coil formers L401, 402, 403, 404, and T405 to be fitted with cores which I removed from an old PMR rig and the only critical thing is that they fit easily into the formers. The ceramic variables in association with the Ls are set at max and tuning done with the slugs (PERHAPS THIS IS NOT THE BEST METHOD !). The trimmer TC405 is removed and replaced with a Murata variable 6-50 pf orange. The tuning line at the PCB edge connector on pin 13 is cut, this is taken to gnd via a 2k7 resistor (max cap from varicaps). That's all just tune up for max conversion gain about 13 dB in my case, you will need a temporary LO at 59.5 MHz at about 0 dBm at pin 17. If you top couple L401 and L402 with 1p5 and L403 and L404 with 1p5 then the conversation gain increases to circa 30 dB.

The TX Exciter PB –1466

This really similar to the RX board but in practice is much more involved, again coil formers L502, 503, 504, 506, and T502 have cores fitted and their associated ceramic trimmers padded with 15 pF. The mixer bandpass filter also has C513 and C534 remove and replaced with a single 3p9 or 6p8 capacitor for increased drive. Again the tuning line is broken and grounded with 2k7. Without doing anything else this will tune to around 50 mW. This could fully drive a Mitsubishi RA30H0608M PA to 30 watts. However to drive the booster the properly the power stages need serious rebuilding and this involves removing L507 and L510 and re arranging the output network in a Pi network this giving about 250 mW which will drive the booster to 15 W without ALC.

I replaced the coils with trimmed toko S18 green coils fitted with an AL core for L507 and a ferrite core for L510 or no cores as required on tune up. C523 is padded with 15 pF and variable TC506 removed and replaced with a fixed 33 pF. C538 is replaced with a 1 nF capacitor and a Murata orange trimmer fitted from the junction of this and the coil S18 green ferrite to ground to form a pi network. I tuned this board using two signal generators for the IF and LO and with -10 dBm IF and nearly 0 dBm LO gives 250 mW at 70 MHz.

The Booster or PA Board PB-1470

The hardest part is getting the board removed as there is a large tab on the SO-239 socket which needs lots of heat to remove, the rest is easy.

Remove all the ceramic variables and replace with Murata orange 6-50 pF, also remove C1201, 1205, 1227, 1224, 1211, 1212.

In place of 1201, 1205 use a Murata orange variable, in place of 1227 use a fixed 68 pF.

Remove L1205 and L1207, these are replaced with coils of these dimensions, 4 turns 20 swg Cu wire, ¼" ID and one wire diameter spacing.

I removed L1211 from the AM Mod line and replaced it on the TX on 13.5 V line as I was not planning on AM operation, your choice. The low pass filter needs re-dimensioned for 4 m, at present I have not done this but use an external LP filter.

For stability a 3 dB pad is added ahead of the RF input to the booster board. Tune up using a signal generator and then finally retune when the rest of the boards have been modified. Current consumption is about 3 ¼ A for 15 watts out. The output network is configured as a LCC and not CLC as in the original. Also it may be necessary to re wind L1204 and L1206, 8 turns 20swg ¼" ID. If there is any instability a RC network of 330R in series with 47 nF from Q1201 collector to base should prove effective.

The Local Board PB-1454

This needs new crystals, 12.28889 MHz for 70 to 70.25 and 12.34444 to cover 70.25 to 70.50 MHz. The low band xtal can be bought close to the desired frequency off the shelf at 12.2888 MHz for about 27 pF.

After fitting the new crystals then pad C240 and C241 with 2p7 and remove C238 and replace with a 39 pF ceramic capacitor.

Retune to 110.6 MHz and check that at least -15dBm is available at pin 3, change to 111.1 MHz and check the result is similar. If using the 27 pence xtal then it may be possible to lift it to 12.28889 MHz with its appropriate trimmer. However you will need to remove C213 30 pF to allow the 12.2888 to pull up to 12.28889 MHz.

The PLL Board PB-1455

This is the only board that needs an add on PCB. This is the divider board.

First however the VCO coil is removed L301 and replaced with a S18 yellow and Al core (or ferrite as needed). Set the trimmer TC301 to half mesh. Fit cores as before into T302 and T303. Then break the wire link to the VCO varicap and connect to a temporary 7805 supply (5 V). Then adjust the VCO with slug and ensure that the band switch is set at 144 this supplies the band tuning voltage. Check that this is 2.0 V and set the VCO to say 118.9 MHz. Then peak the output from the following stages and you should have about 0 dBm at pin 2 Local Out. However +6 dBm is possible.

5.97V = 70.250 MHz
4.78V = 70.000 MHz.

New Divider Board

This was originally built dead bug style just to see if the 74VHC393 was happy at around 120 MHz, this was not a problem.

Build the divider as per the drawing and connect the input to the Local out from PB-1455 and cut the track before it goes to the edge connector, take a 8 V supply from pin 12. The output from the divider then goes back to PB-1455 on the other side of the track break so that it then is connected to the edge connector as the new Local out signal. Approx +4 dBm unloaded or -6 dBm loaded is at this point to drive the mixers.

VCO divider schematic.

Xtal Board

Parts List

RX Board

5 ferrite cores

Murata Orange trimmer, TZ03Z500ER169

2.7 kΩ

TX Exciter

5 ferrite cores

6 x 15pf caps

2.7 kΩ

2 x S18 green

33 pF, 1 nF

Murata Orange trimmer

Booster PA

6 x Murata Orange trimmers

68 pF

2 coils 20 swg

Local Board

12.28889 MHz HC49u

12.34444 MHz Fundamental HC49u

2 x 2.7 pF

1 x 39 pF

PLL Board

S18 green AL

2 ferrite slugs

New Divider Board

74VHC393/74LVX74, OR any flip flop that can divide by 2 at 120 MHz. BF199

Toko datasheet

Technical specification
Inductance Range : Temperature Coefficient :	0.3uH - 45uH 150ppm/°C max	Not recommended for new designs. Please use MC117 Series.
Features
The S18 is a high stability moulded coil for general VHF applications in the region 30 to 200 MHz. The core may be adjusted from either end with the appropriate plastic hexagonal trimmer tool. A metal tool must not be used as it will de-tune the circuit, and will fracture the brittle ferrite core. Three types or cores are available, two ferrite and one aluminium. Also available is a single screening can, B.E.C Ref. 420003. For low level signal receiver coil or for low power areas such as multiplier stages of transmitters. Precise winding positioning is achieved on torsion machine to exact spec before polypropylene former is moulded around it. This assures a constant winding pitch which provides outstanding uniformity in inductance, minimum stray capacitance and optimum Q characteristics at high frequency. A location tab is provided at the base to indicate the starting side of the winding and to facilitate correct positioning into PCB.