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7RHF progress

4 November, 2015 - Reading time: 3 minutes

This last weekend I had some spare time to play with the 10m repeater project.

I turned my attention to the receiver side of things to see if I could get a KL70 receiving down at 29MHz. Thanks to the work of Dion VK7DB, who had done most of the preliminary work on this earlier, I was able to get the VCO to lock down at 29.580MHz relatively simply. Without his help I would have no idea.

The next issue was the front end. I touched the signal generator lead on the mixer to confirm it would receive... it did. I removed two of the bandpass filters from the GE MLS 1 I used for the transmitter. I still had the receiver board.

I hastily connected them up to the tracking generator.

Insertion loss looked reasonable. The MLS also had a HPF on the front end. So I removed that to see what it did.

I put the HPF in series with one BPF. Above is the plot.

The MLS has an IF of 20.8MHz, the KL 21.6MHz. The HPF had a notch at the IF of the MLS which was around 50dB. The bottom of the notch was 56dB at 20.1MHz, perhaps an inaccuracy with my test setup? The reference is 20dB down in the photo above.

Soldered the bandpass filters in place of the original KL70 cans, which I had removed for modding to probably 6 metres later.

It appeared to be receiving quite well.

I inserted the HPF in after the 2nd BPF as it had been in the MLS front end. I measured 70dB of reject at the IF of the KL - 21.6MHz for an additional insertion loss of 1dB. 

A KL450 UHF exciter was installed, and I now have a 10M RX > UHF TX all in one neat KL package. I had a spare KL450 PA lying around, so I threw that in, installed the low power jumper and now have it doing 10W at 2.5A.

I have yet to test the stability of the receiver. Hopefully the VCO doesn't fall out of lock. With all the playing around on the bench and powering on/off it locked everytime. Saturday/Sunday were also warm days in the shed, and it appeared to be fine. Extensive testing will be done shortly.

I also took the opportunity last week to remount the PA and VCO/control board in the 10M transmitter. I added a KL450 RX to the box and it all looks rather neat now.