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Categories | QRP Radios (5 watts or less) | Hendricks MMR-40 Transceiver Help

Show all reviews of the Hendricks MMR-40 Transceiver

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N4QY  Rating: 4/5 Nov 15, 2007 13:00  Send this review to a friend!
Very Good Performance  Time owned: 0 to 3 months
Our radio club has a project contest in December each year, and I chose the MMR-40 for my entry this year. Previous (winning) entries have been the SST 40 meter transceiver and the KX-1 transceiver.

The most complex kit I have built was a Heathkit SB-100 in the 60s when it first came out and have built many other Heathkits as well as some homebrew transmitters. I have also built the 40 meter Stand Alone transmitter designed by Steve Weber. Steve has a very good and unique talent for designing QRP gear. I also have his AT Sprint IIIA, but have not built it yet.

When the kit arrived from QRP Kits, the parts were inventoried and separated. All parts were present. After carefully constructing the unit, and aligning the receiver,it worked just fine.

I was not as successful with the transmitter. I followed the alignment procedure in the manual, but transmitter output was about 1/4 watt on the watt meter instead of the expected 5 plus watts. Listening to the transmitter on a station receiver revealed a horrible sounding signal. I took the IRF 510A final stage off the board, and repeated the transmitter alignment procedure again with similar results.

About this time I was wishing I had bought the Norcal 40A as my project. It will likely be the next kit built.

After much checking and head scratching, I discovered that it is possible to tune T3 and T4 up near 9 Mhz, and the drive signal to the IRF 510A was triple the VFO frequency. With the help of the scope and frequency counter, T3 and T4 were tuned to the 40 m band, and after the IRF-510A was installed again, the output came up to 7 watts. This was more like it.

While testing the MMR-40 with a dummy load, and listening to it with a receiver, the horrible sounding signal was still there. Comments on the Yahoo users group indicated that the transmitted signal would be much cleaner than it sounded in the nearby receiver. However, several cw stations worked commented about the bad tone they were receiving. What was happening was that the carrier and one sideband were both being transmitted. The carrier was not being suppressed adequately so the cw stations on the other end were hearing two tones about 600 Hz apart. Back to the test bench.

This time, instead of strictly following the manual procedure, I put the scope on the output and monitored the signal as the 10 Mhz BFO oscillator was adjusted. The side tone audio frequency signal of 600 Hz wes clearly visible riding on the output signal. Basically, a carrier and 1 sideband were being transmitted. The BFO oscillator was then adjusted until the 600 Hz component essentially disappeared. This meant the BFO was shifted enough that the carrier was being adequately suppressed by the 4 crystal IF filter and the only signal being transmitted was the desired sideband. Power output could now be adjusted to about 8 watts. It would have been very helpful to me if the instructions had mentioned an alternate transmitter alignment procedure if a scope were available or if diffficulties were encountered.

Now the rig was put back on the air for more CW contacts, and no stations have reported problems with the tone. I specifically asked 5 or 6 stations for comments. All said it sounded fine.

The signal still sounded below par in the station receiver, but the received signal on the other end of the QSO was ok. It would have been very helpful if the manual had made reference to this.

I would not recommend the MMR-40 as a first time kit because of the complexity of adjustment and checking required to get a good cw signal. I would also say that a scope is required for proper adjustment and checking of the transmitter.

After getting the MMR-40 properly adjusted, I have been very pleased with the results. The receiver is quite good and more selective than I thought it would be since the IF is wide enough to accomodote SSB signals. The CW audio filter does a good job of narrowing the pass band for cw signals. I have also been pleasantly surprised with the sensitivity of the receiver. The audio output is quite good, and I have used it with an external speaker with plenty of volume. The VFO is quite stable.

In a day of cw operating, I have worked 2 Mexican stations, a Canadian station, numerous US stations and a station in Italy. A Wisconsin station gave me a 599 report and could not believe I was only running 8 watts.

All of my contacts were on cw from North Carolina using an 80 meter Extended Double Zepp at about 75 feet.

Comparing it to my SST, I like the higher power output and the speaker that the MMR-40 has. The SST has better selectivity for cw, but then it won't work SSB either. I may work SSB with the MMR-40 some day after I build a suitable mike.

The MMR-40 will definitely go with me on some camping trips and other portable operations. Right now, I am enjoy using it instead of my several BA stations.

If the instructions had been more inclusive and detailed on transmitter alignment, I would have given the MMR-40 a 5 rating.

I completed my MMR-40 2 days ago. 
Product is in production.
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