Exciter for VHF / UHF transverters

Discussion in 'Homebrew and Kit Projects' started by K9STH, Sep 28, 2008.

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  1. K9STH

    K9STH Ham Member QRZ Page

    Many of the commercially manufactured VHF and UHF transverters (and a number of the kits and homebrew ones as well) require less than 1 watt drive at the intermediate frequency. Now this is unlike the old Hallicrafters HA-2 and HA-6 which can take up to 100 watts of drive.

    Now some of the "modern" transceivers do have a low power output for use with transverters but some do not. And there are those who use older equipment for the i.f. The Collins S-Line and KWM-2 series have a low power output and you "kill" the final amplifier stage by removing the screen voltage (there are jacks on the back of the units for doing this) for use with the 62S-1 transverter. Heath did the same thing in their SB-Line except that the user had to modify the unit (there were parts for doing this that came with the SB-500 2-meter transverter).

    I recently acquired a Microwave Modules 432 MHz transverter in a "trade deal" that requires low power for drive and thought about using one of my S-Lines or Heath SB-Line for the intermediate frequency (28 MHz). The S-Lines already have the low power capability but my SB-Line does not (I use the SB-Line with my Hallicrafters HA-2 2-meter transverter). I considered modifying the SB-Line but, basically, the modification is a real "pain in the posterior". Then I got to thinking. I have 2 Uniden HR-2510 10-meter transceivers and I had previously made an interface box to use the HR-2510 with the HA-2.

    Now the interface box is basically a relay that switches the output of the HR-2510 between the input to the transverter and the output from the transverter. It also switches the transverter from receive to transmit. It did require moving the microphone to the the interface box (because the PTT has to activate the changeover relay before activating the transceiver) and then running the PTT operated by a relay and the audio to the HR-2510.

    All this aside, there are 2 controls on the main circuit board of the HR-2510 that allow the output to be reduced to as much as 500 mW (1/2 watt) without any modification to the unit. One of these controls is labeled "ALC" and that affects the USB and LSB output and the other is labeled "AM Power" which affects the AM, FM, and CW output power. There is one thing with the setting of the "AM Power" and that is when the CW power is reduced to 500 mW the AM and FM go down to about 100 mW. However, at least in my application, I am not going to be using either AM or FM on 432 MHz and the 500 mW CW is optimum for driving the Microwave Modules transverter. Also, using the "ALC" to reduce the output on sideband does not seem to affect the quality of the signal (at least when I listen to the output on the 10 meter band the quality is the same as when running the "usual" 25 watt peak output).

    If, and when, I do not need the HR-2510 as the i.f. for the transverter I can open the case and turn the 2 controls back and get full output. Besides, I have another one that I can still use in my 10 meter mobile.

    Anyway, there are a lot of HR-2510 units "out there" and even though the unit is now on the FCC "no no" list in terms of being sold by commercial firms, they can still be bought used. In addition, there have been quite a few that have had the "golden screwdriver" applied. It has been my experience that all that is required to correct the "golden screwdriver" is to realign the unit. Also, the fact that many units have been "opened up" in frequency is of no consequence because, depending on the crystal in the transverter having the expanded frequency is actually a benefit. It is perfectly legal to use these frequencies as the intermediate frequency of a transverter because the signal is not being applied to an antenna and therefore not being radiated.

    I do not know if the Uniden HR-2600 or the Radio Shack versions (which were made by Uniden) have these power level controls. I suspect that they do but do not take my word for it! Now the HR-2510 only "steps" the transmitter in 100 Hz increments, but that really does not present any problems. But, there is an RIT on the receiver so the receiver can be "zero beated" without any problems at all.

    But, for those who are looking for a relatively inexpensive method of using the transverters that require low power for transmitting the use of these units is a viable option.

    Glen, K9STH
     
  2. WA3EEC

    WA3EEC Ham Member QRZ Page

    As usual Glenn has a great idea.

    I seem to remember however, that several years ago, thee were some notes that circulated in the VHF/UHF community on the use of these transceivers as IF for transverters. If I remember correctly, it was relative easy to unsolder a cap at the receive side of the TR switch and have a separate pigtail for the received input. One then used a 30 dB 5W attenuator at the normal output an thus you had an IF source for a XVERTER and one that would not cook the receive converter.

    Lad WA3EEC
     
  3. K9STH

    K9STH Ham Member QRZ Page

    There are several things that can be done to "split" the single antenna jack so that you do not transmit by accident into the receiver output from the transverter. The reasons that I used a relay to change the jack between transmit and receive that has to be activated before the transceiver can transmit is for added protection and so that the transceiver can be used for its original purpose with a minimum of effort.

    Where the Hallicrafters HA-2 is concerned there is no need to reduce the output power of the transceiver and therefore only the ability to "split" the input/output to/from the transceiver in needed. With the Microwave Modules transverter I did have to reduce the power or else include an attenuator on the transmit input side. In the case of the HR-2510 it was easiest just to turn down the power adjustments. Now if I didn't have a second HR-2510 to use in my mobile then I definitely would have gone the attenuator route.

    Glen, K9STH
     
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