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73 Review r r by Peter H. Putman KT2B

SHF Systems Linear Transverters for 1240 and 2304 MHz

Explore the microwave bands with these easy-to-build kits.

Down East Microwave Box 2310. RR1 Troy ME 04987 (207) 948-3741 Price Class: S140-S310

O ne of the biggest obstacies to increasing the amateur population on our microwave bands has been, and continues to beT (he lack of ready-made equipment at reasonable prices Several manufacturers have offered a line of linear transmit and receive converters (known as transverters) that are ready to run out of the bo*, but at prices that may discourage newcomers

For those with the technical know-how, the best method has been to "roll your ownrp equipment, either completely from scratch or from a kit. if you have access to microwave test equipment, this process isn't all that difficult For those who don't, and who possess only a basic Knowledge of microwave operation il can be an uphill battle all the way with all of the precise assembly and alignment involved!

Things have changed considerably with the advent of microwave monolithic integrated circuits (MMICs) over the past few years. These devices offer broadbanded, no-tune performance with reasonable gain and noise figures at affordable prices MMICs can be used both as low-power RF gain stages and as RF amplifiers on receive, and they are reasonably stable in operation

SHF Systems has introduced a line of linear transverters which make extensive use of these devices, along with etched mtcrostnp circuitry. As a result, even the basic kit builder can be up and running on several microwave bands with a minimum of test equipment and time. ¡Ed. Note: Down East Microwave is the sole distributor of the SHF Systems kits.}

The SHF Transverters

Currently, SHF Systems offers transverters for 902 MHz, 1296 MHz, 2304 MHz, and 3456 MHz. In each case, the complete trans-verier consists of a local osdflator (i_0), transmit upconverter, and receive down-converter. All three are located on one PC board on the 902 MHz version. The other three use a separate LO board. Our review versions (SHF-1240 and SHF-2304) are very similar in operation and appearance, although the SHF-2304 transverter board is smaller In size. Both use the same LO circuit, with different crystal frequencies, and both systems use an intermediate frequency (IF) of 144 MHz, making them a natura) tor use with 2 meter multimode equipment, and even 2 meter FM transceivers.

The key to a stable microwave signal is a stable local oscillator. The SHF-LO employs a 2-stage circuit of BFX89 devices, functioning as a crystal oscillator and buffer amplifier. A series of MMICs and one HP2B35 diode multi

Shf Amateur

Photo A, The SHF-1240 transverter board (1296 MHz). 40 73 Amateur Radio Today • February, 1991

ply the signal into the 540-580 MHz range. Two 3-stage bandpass filters and one low-pass filter ensure a clean signal at the output. An option ailows the user 4 dBm more gain (required for the 2304 input).

For 1296 operation, the LO signal is doubled by another HP2B35 dtode into two more MMICs and associated filters, resulting in an LO injection frequency of 1152 MHz Both 144 MHz IF ports are coupled lo a pair of Wilken* son splitters in a "rat race mixer scheme At 2304 MHz, operation is similar except that the 4th harmonic of the LO ts selected (2i 60 MHz} and filtered before injection into the Wilken-son splitter.

Actual TX and RX mixing is performed by a pair of HP2835 diodes on the SHF 1240, while a tiny diode pack of HP-HSMS2822 diodes do the trick at 2304. In either case, there are no tuning adjustments to be made, only some caretui soldering when installing these diodes. These mixers are quite sensitive, as only 1 mWof energy at 144 MHz is required for drive.

Both boards are completely symmetrical. This means that either side of the board can be used as a receive or transmit converter, or that both sides could be used for the same purpose. As in the LO, no tuning adjustments are necessary. Depending on the modelh different MMICs are used as TX and RX gain stages with 3-pole bandpass fillers between the cascaded gain stages.

Although the noise figure performance of the MMfCs used is quite good, a GaAsFET preamplifier on the RX side will yield noticeable improvement, Typical power output on both boards is in the range of 10 mW, but higher outputs can be obtained with more drive and LO injection. The RX conversion gain ts typically 20-25 dB, more than enough to drive the front end of a 2 meter multimode transceiver.

Construction

The manual for the SHF LO slates that it can be built in under two hours I took just about iwo hours to be extra careful, since the case lead identification on the various MMiCs can be confusing. For the record, targe case MMICS (such as MSA-0404 types) have a dot on the output lead, and smaller MMICs (such as the MSA-0685) have it on the input tead Most cases of trouble with these kits are a result of incorrect lead positioning.

You won't need much test equipment to

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