10 GHz

This will be a collection of notes and a timeline of sorts as I work on exploring a new band.

January, 2022

I have been intrigued by the idea of trying microwaves for years but I thought it would be near hopeless trying to make contacts from my location. The vast majority of 10 GHz activity is portable where one can select favorable locations. Operating portable is not an option for me. It would be my home station or nothing. I am not on a hill, my horizon is imperfect and I am a long way from any other 10 GHz stations. I was aware of rain, snow and aircraft scatter but perusing the various web pages and articles I had access to did not turn up enough information to assess my chances. I found a good amount of information on how these propagtion mechanisms work but little to nothing regarding what one could realistically expect for a given station setup. When I did find web sites or videos with information about specific QSOs that were made, there was often no information given about power or antenna gain. Over the last year or two there has apparently been a surge in 10 GHz activity. It seems this has resulted in an uptick in videos being posted to platforms such as Youtube. Still, information about equipment used was often incomplete. I also read an article by KA1GT about a very low cost 10 GHz receiving setup. This, combined with the loss of 2200 meter operation pushing me to look for a new challenge, led me to seriously consider trying 10 GHz. The other challenge is getting above the trees. Fortunately the trees top out at about 95 feet and I have two towers taller than that. One is 96 feet, the other 104 feet. While rebuilding from storm damage in 2021 I reserved a spot on a mast at 105 feet for a small 10 GHz dish.

Since I was seriously considering starting out with a low cost receive setup to explore the potential of my location, I became particularly interested in beacons. Since most 10 GHz activity is from portable operations and the majority of QSOs are coordinated in some way, it didn't seem likely I would be hearing much unless I could hear beacons. I had questions about this since beacons often have much less antenna gain than a typical 10 GHz station. I went on a search for information about hearing beacons on rain, snow, or aircraft scatter but found next to nothing. Did this mean beacons are too weak to be heard at distance using these scatter modes, or was it simply that no one was posting information?

My horizon profile from planned location of 10 GHz dish generated by HeyWhatsThat

The next thing I did was join several 10 GHz and microwave forums. The people on the forums are very friendly, outgoing and generous. They seem eager to help. There I started asking questions about propagation and what to expect from my imperfect location given the size of station I felt I might be able to put together. Based on information gathered in that way, 10 GHz sounded much more promising. Over several months digging through forum archives, reading new posts and watching videos shared there, my perception of what is or might be possible continued to evolve. Even so I felt I wasn't getting a solid picture. I developed a strong perception that what is known within the microwave community regarding possibilities and expectations is largely not known outside the community. Is 10 GHz one of the best kept secrets out there? I hoped to find out.

At this point, after several months with some view "inside" the community (only by way of the forums) I still feel I have a poor understanding of what to expect, though it has greatly improved. I still perceive a large gap between knowledge inside the community and information that gets outside it, particularly in the area of possibilities and expectations. Only time and experience will show whether this perception is accurate. I may be coming to this in an unusul and particularly isolated manner. Once again I only have perceptions to guide me, but from what I can gather most newcomers to microwaves have some opportunity to connect in person with those areadly involved, including being a participant or observer in portable microwave operations. I do not have such opportunities, which makes me far more isolated and out of the loop.

I haven't asked but I might have access to a potential beacon site as well. The tower is owned by a local ham radio club. I own one of the repeaters on the tower. I know I can't afford it but I can't get the idea of a 10 GHz beacon out of my mind. In these days of very affordable 10 GHz receive systems, might beacons play an important role in attracting newcomers?

Potential beacon horizon profile generated by HeyWhatsThat

I don't want to start off on the wrong foot with the 10 GHz community I hope to join but I am one to tell it like I see it. If I am being honest, I give the 10 GHz and microwave community a failing grade on getting information out there to help prospective newcomers understand the potential. There is not enough out there to help someone who is isolated or not solidly connected to the community evaluate the prospects of the band. I find this unfortunate and disappointing. I am increasingly finding that a lot of stuff that would be very helpful in this regard, such as videos of actual reception or QSOs, is only being posted temporarily and its availability is only known within the microwave community. I will be on a mission to do whatever I can to improve the situation. As I learn and discover what can be done from my location I will post things here, on my blog, and on Youtube. I hope to have a receive-only system ready to go on the tower in the early Spring. A full transceive system is a long way off due to budget constraints.

January 13, 2022

Today I did initial testing of a 10368 MHz signal source and the LNBF I hope to use for a receive-only system. The signal source is an old Qualcomm synthesizer board (thanks N1JEZ) modified to produce 1152 MHz. It should be producing harmonics that fall in several ham bands: 2304, 3456, 5760, 10368 and possibly 24192 MHz. The 10368 signal is quite strong listening with the Bullseye 10 kHz LNBF in the next room. The LNBF converts 10368 down to 618 MHz which I run into one of the cheap RTL2832 SDR receiver sticks. I mounted a switch on the side of an equipment rack to control 12V to the LNBF. At this point nothing has been calibrated. I am still using the original 10 MHz OCXO reference on the Qualcomm board, I am certain the RTL2832 stick is off frequency a bit and though the Bullseye 10 kHz is one of the more accurate if not the most accurte LNBF in terms of frequency, it is likely not perfect. Getting some of the frequency errors and drift under control is next on my list of things to do.

February 22, 2022

Completed work on the weak signal source. Removed 10 MHz OCXO from Qualcomm board, replaced with external Bliley NV47A1282 on a VA3TO board (thanks to VA3TO). After a day or two of testing I feel that I know where I am to within 30 Hz at 10 GHz. Oscillator aging may require frequency adjustment to maintain that level of precision but I can easily do that since I have a GPS ereferenced HP counter.

March 15, 2022

Over the past few weeks I have been working on a power and SWR (return loss) meter. The first trial run used a $25 power sensor board from China using the AD8317 chip. Others have had good luck using boards like this but mine was terrible. It was sort of OK at 1 to 2 GHz but not a good fit to the curves for 900 and 1900 MHz in the AD8317 datasheet. 2 GHz is the limit of my in-house testing capability. It was unreasonably poor at 144 MHz. That plus the board being .062" thick which I understand is not good at 10 GHz led to me lose all confidence in that board. I suspect getting a good one is a matter of luck. For the first attempt I was using the Arduino Nano. Here is a picture of this failed atteampt at the project.

I decided to try the much more pricey ($144) Analog Devices AD8317 eval board. It looked much better. At 900 and 1900 MHz its performance closely followed curves for those frequencies in the AD8317 datasheet. At 144 MHz it looked far better than the cheap boards, though calibration was significantly different than at the higher frequencies. I also was not happy with the code I was using for the Nano. It was going to require a lot of work to get it where I wanted to end up. I used to be a fair PC software developer back in the 1990s but had not written a line of code in 20 years prior to taking on this project. I then learned of another approach and obtained different code from another 10 GHz operator who is working on a similar project. As a matter of convenience I switched to Arduino Uno R3 with LCD keypad shield. This greatly reduced the breadbording reauired, as well as conveniently provding several buttons for controlling the meter. Here are a couple pictures of the test setup with this implementation. The top line of the display shows the reading (here power in dBm) while the bottom line is a bar graph which can be very useful when tuning things.

April 19, 2022

Progress has been a little slow but I have several projects in the works. Today I did final assembly on the sensor head for power and return loss measurements. A connectorized DC power feed might have been preferable but was not within my capabilities in very limited space. Small size and light weight were important goals. The connection is well strain relieved and should hold up for quite a while. The DC power feedthrough filter is a #4-40 size from Downeast Microwave. Thanks to W1GHZ for generous assistance. Several parts have been sent out for characterization on a VNA, including the directional coupler, SMA short and SMA termination for this project.

I calibrated the power sensor for all bands 1.8 MHz to 903 MHz. I also calibrated at 1000 and 2000 MHz, which is as close as I can get to the 1296 and 2304 MHz bands, but should be close enough. The reading has about 2 dB of jitter at 1.8 MHz. All higher bands are OK. Calibration changes by 3 or 4 dB as I work my way up through the bands. Useful dynamic range is 60 dB on all bands checked so far (-60 to 0 dBm). It will be less on 10 GHz but should be at least 40 dB there. I will need to send it out to be calibrated for 10368. If whoever I send it to has time, I will have it calibrated for 3400 and 5760. It would also be interesting to have it checked at 11 GHz to see if it is still useful there. That might be good to know when it comes to making return loss measurements. The calibration process was boring to some...

I never seem to take the shortest or quickest path to anywhere. I decided to put a beacon on the PARC/N1BUG repeater tower. Club members and leaders have been enthusiastic and very supportive. The beacon is a major expense and that slows down progress toward getting my home station 10 GHz capable but it will be eductional and helpful to me and perhaps others. Initially the beacon will be 10mW, 2x12 slot antenna and GPS locked. There may be a future upgrade path to 2 or 3 watts. Such an upgrade would have to be discussed with the club. I will consider that if the beacon would be of use to those outside the line of sight area.

April 30, 2022

I love it when a project finally comes together! The power and return loss meter is complete. All that remains is to send it out for calibration at 10368 (and perhaps 3400, 5760, 11000). Thanks to W1GHZ, W3IP, N8ZM and others for helping with this project.

May 3, 2022

Barn find. With help from local hams I just dragged home this 6-foot dish found in a barn just five miles from my house as the crow flies. What are the odds of that in rural Maine? I have no idea what frequency this was designed for or how unkind years of storage and transport have been to it. But it was free so why not? I also got about 10 feet of WR90 waveguide with flanges I don't recognize. The rectngular flanges have eight holes but are significantly larger than the eight hole flanges on my other piece of WR90. There is also a few feet of what appears to be WR159. Thanks to NC1Y for the dish, KB1WEA, K2KJ and KB1WRZ for help with transport.

Last update May 3, 2022