Hi, I am Tony I0JX
Enjoy building a low-cost kit for the 4-meter (70-MHz) band

Rev. 4 - July 23rd 2007



The 70-MHz band (4-meter) is getting available in more and more European countries (see http://www.70mhz.org/) and recently also in Italy (see http://www.space.it/70mhz/). In period mid-May / mid-August of every year long-distance QSOs are possible via sporadic-E propagation. Moreover, during sunspot cycle peak periods, it should also be possible to have transequatorial QSOs between the Mediterranean area and South Africa (ZSs are allowed the 4-meter band).

Availability of radios supporting the 4-meter band is still rather scarce, and many amateurs then use a transverter hooked-up to their HF or VHF rigs (a transverter is a device permitting a transceiver designed to operate on a certain frequency band, to also operate on another band). 

A particular cost-effective approach is to get a 6-meter Ten-Tec transverter kit which delivers 8 Watt RF, and modify it for 4-meter operation at assembly time.  The modification is here descrìbed with reference to Ten Tec mod. 1209 which is designed to work in conjunction with a 144 MHz transceiver capable of delivering 5 W RF. After the modification, the mod. 1209 transverter traslates the 28 MHz band (instead of 144 MHz) into the 70 MHz band (instead of 50 MHz) and viceversa.

It now seems that the mod. 1209 transverter is no longer available, while the mod. 1208 can certainly still be purchased (see http://radio.tentec.com/kits/Transverter). The only difference between the two is that the mod. 1208 has a 14 MHz input frequency (instead of 144 MHz). Considering that the proposed modification anyway requires moving the input frequency to 28 MHz,  there should be little difficulties in modifying mod. 1208 instead of mod. 1209. The mod. 1208 transverter can be ordered directly from Ten Tec at price of 159$ (+ postage and applicable taxes), paying with a credit card.

Please however note that the modification described in Sect. 2 is strictly valid for mod. 1209. Therefore, should one have to modify the mod. 1208 transverter, what written there should be appropriately interpreted. Utilizing mod. 1208 one could even conceive not to modify at all the input circuitry so getting a  14 - 70 MHz transverter.



2.1 General

The extra cost for changing the model 1209 transverter from the 6-meter to the 4-meter band is modest, as only some plain extra components have to be procured. An exception is represented by the conversion crystal, an item that you may probably have to expressly order from a crystal manufacturer and that could cost 10 to 20$. Moreover, it could be a fairly long-lead item.

At this regard there are two main possibilities:

The possibility of using the modified transverter in conjunction with a 2-meter transceiver (as the model 1209 originally does) has not been considered, the required crystal frequency being too close to the operational band, this possibly causing spurious emission problems.

The modification described in the subsequent sections refers to the first approach (i.e. using a 42-MHz crystal); however in Sect. 2.7 there are some considerations on the second approach (i.e. using a 94-MHz crystal) should you want to go that way.

The proposed modification is fully reversible, and you can then get the transverter back to work as originally designed by just replacing the changed components and re-tuning the transverter itself.

The Ten Tec transverter is designed for transceivers delivering 5 W output. Modern transceivers permit to reduce output power down to 5 W, but in some cases this may not be possible. If you have problems at this regard, the simplest solution would be to insert an attenuator (capable of handling sufficient power) in between the transceiver and the transverter. This will clearly also cause an attenuation on the receive path, but this should not be a problem because the transverter receive gain is very high and attenuating the signal would anyway be advisable (the receiver noise figure would remain virtually unaffected).

Alternately, you could take a low-level transmit signal from your transceiver (some of the modern transceivers often provide for that signal), but you shall then accordingly modify the transverter input circuitry.

The modification consists in varying the value of some components and adding some extra components. The following picture shows the board, where the modified coils and the added trimmer capacitors are indicated.


We assume that you are going to assemble an unmounted kit. Accordingly, in the following the various phases described in the Instruction Manual are separately addressed.

Remember that wherever in the manual you read:


2.2 Phase 1.0

Circuit Board Preparation Step

Mount all components as instructed, except for TP2 which is useless and must be omitted to leave room for trimmer Cb (see Sect. 2.5).

94 MHz Crystal Oscillator Board and Diode Mixer

Some of the components must be changed with others of different value:

Mount all components as instructed.

Then add a 20 pF trimmer (Ca) in between Q6 collector and ground.

Test procedure does not change except that, where it asks you to adjust the L23 core, you shall instead adjust Ca. Should you be unable to zero beat the test receiver at precisely 42.000 MHz, then you could try putting a 10 pF capacitor in parallel to trimmer Ca, or rewinding L23 with one turn more or less. Remember that one of the reasons why your oscillator may not be right on frequency is that the crystal manufacturer has not cut it for series resonance.


2.3 Phase 2.0

T-R Voltage Control, RF Input Attenuator

Some of the components must be changed with others of different value:

Mount all components as instructed.

Test procedure does not change.


2.4 Phase 3.0 - 50 MHz and 144 MHz Receiving Amplifiers

Part A: Receive T-R Switching at 2-meter Input

Some of the components must be changed with others of different value:

Part B: 144 MHz post amplifier

Some of the components must be changed with others of different value:

Part C: 50 MHz Receive Pre-Amplifier

Some of the components must be changed with others of different value:

Mount all components as instructed.

Solder the shield cans of L19 and L20 on both sides of the printed board.

With regard to testing, please proceed as follows:

No other tests are required for now.


2.5 Phase 4.0

Low-level 50 MHz Transmit Circuitry

Caution: the capacitor which is marked C21 in the electrical diagram is instead marked C22 in the printed board, and viceversa. We here adopt the electrical diagram numbering.

Some of the components must be changed with others of different value/type:

Mount all components as instructed, but C17, C23, R27 and R30 that shall be simply discarded.

Solder the shield cans of L8, L9 and L10 on both sides of the printed board.

Then add:

Finally, fully remove ferrite core from L8, L9 and L10.

With regard to filter peaking, please proceed as follows:


2.6 Phase 5.0

Transmit Driver, RF Amplifier, Low Pass Filter

Just one component has to be changed with another of different value:

Mount all components as instructed, but C40, R44 and R46 that shall be simply discarded.

Test procedure does not change.


2.7 Using the 94-MHz Crystal

I have not tried using the original 94-MHz crystal (thus having to operate the transceiver in the 24-MHz range), so I can only give you some hints at that regard. However I see no reason why problems should occur using that crystal, apart from the operating inconveniences mentioned in Sect. 1

Should you decide to use the 94-MHz crystal:

I presently see no need for other changes to the modifications.


2.8 Other Modifications

If you wish to have the possibility of varying the output power independently of the 28-MHz drive power, just add a 22-ohm potentiometer (even if wire wound) on the front panel, and connect it in parallel to R6 (47 ohm), using a short length of coaxial cable.

If you need to key the PTT of an external linear amplifier, just mount an RCA socket on the back panel and realize the circuit shown below (which will drive a positive PTT line). Use an NPN power transistor, at least 80 V, 1 A.



On a dummy load:

With regard to reception:

Good luck and 73


Tony, I0JX

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