6cm Project
So, time to try to realize a new project. I have done the 3cm project and it is working. From my QTH it is quite hard to get long distance contacts. SM7ECM is 222km away, and is about the distance for 10GHz I make at the most. Some of the Danish amateurs has also been worked. That said, the cost / QSO is high. Transverter, PA and parabola cost.
6cm is even less to work here. I doubt I will hear many stations. BUT I want to try.
SM6VFZ is an old radio amateur friend (he is not old), he is a very good RF-designer. He has written in DUBUS magazine many times, and he also work in the RF industry. He had an idea of building a 6cm transverter. It is not (as for now) an available kit. But I have the possibility to try to put things together. He made it easy for me to get started.
So, LO, mixer, front-end and PA is needed. My IC-9700 is my IF working at 144MHz. To lower the IF images 432MHz could have been used as well.
Daniel has constructed a very versatile LO board. This board is now locked to 2808MHz. To be able to use it on 6cm the LO needs to be doubled. It is possible to use a frequency doubler to generate the needed 5616MHz for 144 IF, and then a suitable mixer.
Daniel preferer’s a sub-harmonic mixer. I have not made one before, so let’s try.
The schematic of the sub-harmonic mixer:
144.4MHz resonate frequency yields 100pF and 12.15nH inductor. The inductor can be made 2 turns 6mm diameter 9mm long.
If the mixer is constructed well, it can be very efficient. I used RO587 0.8mm laminate, which is low loss. However, my layout is very basic. The losses in my mixer are about 15dB. But my parashoot in this is my small Chinese LNA. Despite the loss I can add gain and move on. Of course, would a perfect mixer be better.
This means that I could go only with Chinese LNA’s and omit Daniels front-end and only use the 2808 LO. But his front-end is very nice, and has a nice low noise figure. One of the Chinese LNA’s in the picture has a NF < 1 dB. For my 6cm work that will do.
I have mounted the basic set on a double-sided PCB board. I made a double 5760MHz BPF of plumbing cups. The filter work well. The loss @ 5760 is about -2dB.
LO, sub-harmonic mixer and filter on this side:
The other side consists of the RX/TX front end and a dc-dc step-down module.
With everything connected have 0dBm IF in and 2dBm 5760 out. IF rejection is about -30dB.
I guess I will receive comments that this can be better. However, I will try this approach.
The PA. Well nowadays it is not really hard to find PA’s in the 50 =>100W range for 6cm. The one I found is the YPM5850C. It is a jammer for 5.7GHz drones. It is available on different sources on the net. The specification is 47dBm out with 42dB gain.
The jammer function is the VCO to the upper left. Of course, needs this to be removed.
I could not get more than 45.08dBm out (with my measurement uncertainty) which yields 32.2W out with about 2-3dBm drive. Which makes the specification fair, but not 50W out.
+45dBm on 6cm is not bad, so why not leave it there.
RX is not fully tested. However, the close beacon SK6MHI @ 5760.800 could be read 59 from tree reflections.
A small video:
Antenna:
My antenna is a small dish measuring 400x300 and has a gain of 24dBi. This is not so much gain, but the small size makes it easy to install or to bring.
Ideally, I would like one of this antenna big brother. But since the space on the roof is limited, I must have some kind of self-control before buying a new one.
2 of the big brother grid parabola antennas. 3dBi or 6dBi more gain is tempting.
This project will go on, it has no real time plan. Hopefully a 6cm station will be ready.
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