Since the frequency difference of a couple of my modules falls within my SA/TV-test-set receive range, I could try WBFM modulation. I used the same modulator of my HB100 10 GHz transmitter, without decoupling-smoothing capacitor across +5V/GND. The audio was signal fed through the IF port.
Modulation did work, but I was probably overdriving something because the spectrum looked awfully wide and jagged.
CDM324 can be modulated on the +5V line too, so there are two ways to do it.
But .... it is more than 3 times as sensitive as an HB-100, so much more care must be taken on the electronics side.
04 November 2019
03 November 2019
First check with CDM324 couples
As I did on 10 GHz back in Spring 2017, I checked the frequency difference between my 3x CDM324 modules. Currently I have no means to measure a frequency at 24 GHz, so I trust that they are in the ballpark.
Test setup is as follows:
Samples 1-3 were not detected on the first two instruments, but the SA put them about 70 MHz apart.
With the couple 2-3 I should be able to understand how they are spread around 24.125 GHz :-)
This result also confirms that there is no low pass filter on the IF output of these things, so they can be used with an external "receiver" to demod WBFM.
Test setup is as follows:
- put two radars in front of each other at 20-40 cm distance
- power them up and pick the IF output of one CDM324
- feed the IF output signal to an
- oscilloscope
- frequency counter
- spectrum analyzer
Samples 1-3 were not detected on the first two instruments, but the SA put them about 70 MHz apart.
With the couple 2-3 I should be able to understand how they are spread around 24.125 GHz :-)
This result also confirms that there is no low pass filter on the IF output of these things, so they can be used with an external "receiver" to demod WBFM.
02 November 2019
Size of CDM324 vs HB100
Three CDM324 24 GHz radars have arrived. This is the size comparison vs the 10 GHz counterpart HB100:
The CDM324 has no holes for attaching it somewhere, so you need a daugtherboard behind it which acts as a driver too.
The CDM324 has no holes for attaching it somewhere, so you need a daugtherboard behind it which acts as a driver too.
30 September 2019
I will try WBFM on 24 GHz
I know I haven't told you yet about my achievements on 10 GHz and plans for the future, but I want to leave a trace on the Web that I will do some experiments with 24 GHz (twenty-four GHz) radars. The reason I write this short post is that I found no reports of HAM WBFM experiments involving CDM-324 / IPM-165 or other InnoSent and similar 1.3 cm modules. Neither positive nor negative. Nothing.
I have ordered three CDM324 radar modules to play with. They are not tuneable, so I hope they will not be right on the same frequency! I will detect their frequency difference, test the WBFM modulation process and then move to distance without and with dish.
So, in case you are interested in these experiments, or you have already been there, please get in touch!
I have ordered three CDM324 radar modules to play with. They are not tuneable, so I hope they will not be right on the same frequency! I will detect their frequency difference, test the WBFM modulation process and then move to distance without and with dish.
So, in case you are interested in these experiments, or you have already been there, please get in touch!
BTW, in case an InnoSent representative reads this: I would like to test IMS-944 module but it is not easy to buy as a private customer.
24 August 2019
Zagreb Hrelic flea market
Hrelic, at last! In August 2019 I could spend a whole Sunday in Zagreb, which means I could visit the large open-air flea market (every Sunday morning).
It is no different from other flea markets, of course! Lots of clothes and books (99.5% in Croatian, obviously), mechanical stuff, fishing equipment, very little electronics. I noticed that there was almost no stuff from 1970's, because Croatia at that time wasn't as wealthy as it is now and their borders (Yugoslavia) were closed to many Western products. Most sellers place their stuff on the ground, so be prepared to bend if you spot something that catches your interest.
It took us two hours to walk through 90% of the stalls, but consider that only 70% of them were occupied. And by noon they started leaving! Therefore plan you timing accordingly, if you are serious about finding something unique (for you ;) ).
I bought a working Canon VHS videocamera/camcorder for less than 100 kn and a vintage 4.5V flashlight for 1 kn. The first item will donate the CRT viewfinder to a clock/display project while the flashlight will need some restoration of battery contacts before being usable again.
How to get there.
You can get there by tram and walk about 1 km on the Western bank of the river Sava. Or you can go by car, pass the used cars market and enter a large parking area (10 kuna/stay in 2019). Note: throughout the 1 km walk there are occasional "pirate" sellers, that you'll miss if you go by car.
It is all in open air. Hot in a sunny Summer day, freezing cold in Winter. Dress accordingly! I was lucky to be there in a cloudy August day, which was perfect.
You can buy food and beverages at few kiosks spread around the area, if you aren't looking for a modern cozy romantic restaurant :) I didn't look for toilets.
It was a positive experience and I will pay another visit when I have a chance.
 |
| Zagreb Hrelic flea market, August 2019. |
It took us two hours to walk through 90% of the stalls, but consider that only 70% of them were occupied. And by noon they started leaving! Therefore plan you timing accordingly, if you are serious about finding something unique (for you ;) ).
I bought a working Canon VHS videocamera/camcorder for less than 100 kn and a vintage 4.5V flashlight for 1 kn. The first item will donate the CRT viewfinder to a clock/display project while the flashlight will need some restoration of battery contacts before being usable again.
How to get there.
You can get there by tram and walk about 1 km on the Western bank of the river Sava. Or you can go by car, pass the used cars market and enter a large parking area (10 kuna/stay in 2019). Note: throughout the 1 km walk there are occasional "pirate" sellers, that you'll miss if you go by car.
It is all in open air. Hot in a sunny Summer day, freezing cold in Winter. Dress accordingly! I was lucky to be there in a cloudy August day, which was perfect.
You can buy food and beverages at few kiosks spread around the area, if you aren't looking for a modern cozy romantic restaurant :) I didn't look for toilets.
It was a positive experience and I will pay another visit when I have a chance.
21 August 2019
LNB current consumption
My 10 GHz LNB draws 106 mA regardless of the voltage. And apparently it works down to 8V: battery power for /P is possible!
Actually there is a 5V regulator inside the LNB, so it is possible to bypass it and feed 5V from a USB power bank.
Actually there is a 5V regulator inside the LNB, so it is possible to bypass it and feed 5V from a USB power bank.
22 June 2019
A second dish for 3 cm
I got a surplus 40 cm parabolic reflector for my 10 GHz experiments.
It doubles the caravan set where I will mount the LNB and use in the
receive chain. Since the caravan set can be mounted with a suction cup, it
will probably stay on the roof of the car, while the TX dish has to be
adapted to sit on a photographic tripod.
The picture depicts the way I found to attach it to the tripod: a removable vice. The tripod is lightweight, but on a field without vegetation I don't need to extend it fully, so the center of mass will be as low as possible.
Then I needed to see how it performs, depending on the position of the TX signal vs focal point. Here things got interesting. We have installed locally up in the mountains a WebSDR equipped with just an LNB pointing towards the Pianura Padana. It covers 10368.0-10369.0 MHz and receives signals beyond 300 km. It is at about 40 km from my home, slightly behind a building, into the Fresnel zone I dare to say.
The "red cover" TX was put into service. Its TX patch antennas are quite off the focal point, closer to the dish and on a side. The resulting beam, as seen on the remote RX waterfall is quite wide, with strong sidelobes. I could not get a null.
Then a second TX head "white cover" was tried. It is shorter and
closer to the focal plane, slightly lower than the focal point. The beam
is sharp now! Because of the RTL-SDR AGC I cannot estimate the gain,
but any movement impacts the signal strength, move few degrees and it is
gone from the waterfall!
I am worried that dealing with two dishes will make beaming twice as time consuming, but at least the HB100 TX has a form of passive thermal stabilisation that keeps it relatively still in frequency once it reaches equilibrium.
Unfortunately the dish weight makes it difficult to make smooth movements on the cheap tripod, but that is what I have for now.
Last but not least, going from about 25°C (home) to full sunshine (35°C, not measured) resulted in 2 MHz frequency change downwards of the whole system. Good to know when arranging for real QSOs!
The picture depicts the way I found to attach it to the tripod: a removable vice. The tripod is lightweight, but on a field without vegetation I don't need to extend it fully, so the center of mass will be as low as possible.
Then I needed to see how it performs, depending on the position of the TX signal vs focal point. Here things got interesting. We have installed locally up in the mountains a WebSDR equipped with just an LNB pointing towards the Pianura Padana. It covers 10368.0-10369.0 MHz and receives signals beyond 300 km. It is at about 40 km from my home, slightly behind a building, into the Fresnel zone I dare to say.
The "red cover" TX was put into service. Its TX patch antennas are quite off the focal point, closer to the dish and on a side. The resulting beam, as seen on the remote RX waterfall is quite wide, with strong sidelobes. I could not get a null.
 |
| Second TX head. |
I am worried that dealing with two dishes will make beaming twice as time consuming, but at least the HB100 TX has a form of passive thermal stabilisation that keeps it relatively still in frequency once it reaches equilibrium.
Unfortunately the dish weight makes it difficult to make smooth movements on the cheap tripod, but that is what I have for now.
Last but not least, going from about 25°C (home) to full sunshine (35°C, not measured) resulted in 2 MHz frequency change downwards of the whole system. Good to know when arranging for real QSOs!
20 June 2019
Thermal isolation for HB100 transmitter
The actual frequency of an "HB100 10 GHz radar doppler HAM RTX module" is very sensitive to external factors: supply voltage, proximity, temperature.
Voltage is easy to stabilize. Proximity too, and if the IF port it becomes less sensitive.
On the other hand, temperature has a devastating effect, both on short and long term. On the long term, the frequency will drift until the HB100 reaches a constant temperature. But even a quick breeze will produce a snake on the waterfall. So, in order to minimize the effect, I found my way to add short-term thermal inertia to my 10 GHz transmitter:
Variations on long term ("minutes") will still occur, but at a slower pace so that it's easy to do a manual AFC on the receiving side. And the trick is to let it reach a "working" temperature before use and avoid variations over the whole QSO.
Voltage is easy to stabilize. Proximity too, and if the IF port it becomes less sensitive.
On the other hand, temperature has a devastating effect, both on short and long term. On the long term, the frequency will drift until the HB100 reaches a constant temperature. But even a quick breeze will produce a snake on the waterfall. So, in order to minimize the effect, I found my way to add short-term thermal inertia to my 10 GHz transmitter:
 |
| Transmitting end on 10 GHz, modulated on the IF port. |
Variations on long term ("minutes") will still occur, but at a slower pace so that it's easy to do a manual AFC on the receiving side. And the trick is to let it reach a "working" temperature before use and avoid variations over the whole QSO.
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