Building a 10GHz band HAM tranciever from hughes VSAT hardware

[Amper]

Hi!

A while ago i found a whole lot of used Hughes VSAT outdoor units on my local scrapyard. Obviously i had to rescue them not knowing what to do with them. These units turned out to be pretty neat Ku Band transmitters and the LNBs fit the needs of the 3cm band perfectly so over the last weeks i poked around inside of them a bit disabling the interlocks and converting them to work on the 3cm band both ways.

As some requested i will now write down some of my findings in this thread so if you get your hands on similar hardware you may not have to do all this work yourself.

First of all i will have to give credit to all the people in the first thread for helping me as this is my first time dealing with such frequencies and i had to learn a lot along this Project. (i still dont claim to be an expert and i have definitely not understood all that i have done here but wth its for learning anyways.)
https://www.eevblog.com/forum/rf-microwave/changing-ghz-vco-frequency-range/

The second thanks goes out to some guy who previously used one of these units but only using the PA stage cutting away the other parts of the boards to build a 10GHz beacon. I used his work to understand the basics and get started on mine.
www.ka7oei.com/10gig_1watt_vsat_PA.html
(it seems to be offline atm, lets hope it will come back)




If you notice some mistakes i did or have suggestions feel free to tell me. I will write this as a summary of what i have done so far but im pretty sure there are people around here who can teach me a few much appreciated things!

(I will keep posting, dont worry, dont have much time recently)

[Amper]

Rough description of the original hardware

There is two different kinds of outdoor units and each have many iterations over the years. According to stickers and date codes they range between 1999 and 2006. The newer Models have a slender unpainted housing at roughly half the width of the older units and have 2W TX @ 14,5GHz. These units are less complicated on the inside but turned out to have some difficulties regarding conversion to lower frequencies as they have a final PA that according to the datasheet has no gain at frequencies below12GHz which is really sad as they would be much nicer to be carried around. Maybe at some point i will still try to get one transmitting but my hopes are low.

The older Units consist of a water tight die cast aluminium housing with a waveguide output (WR75 with different hole pattern) on one end and an N connector on the other.  On the Bottom there is two F connectors one of which is connected to the LNB.

The attached wave guide system differs between the versions but they all seem to be built similarly just with alterations in flanges and some times different LNBs.

New unit complete:



Old unit without horn:




The accessories can be unbolted and the lid removed, depending on the state the devices are in screws may snap as the stainless tends to gall and rot into the aluminium parts. Inside the following boards may be found:

Newest Version:



Oldest Version (even with factory bodgewire ) :


And the Version i will pay attention to from now on:



As you may have already observed they roughly consist of a few diplexer stages taking apart the input signal into the device next to the DC filtering, protection and regulation. The Signal coming from the indoor unit will consist of multiple frequencies for control, signal and LNB.

The entire upper, unshielded half of the board is essentially just power management and bias regulation for the rf ICs. There is no intelligence or logic whatsoever, just apply the right frequencies and this thing will transmit wich makes the modification pretty simple.

The RF path is also pretty straight forward. The large VCO box in the middle is a very ancient design and also has no intelligence built into it, just two active components and a buns of passives. You may find more detail in the thread linked in the first post here.

The VCOs output is amplified, filtered and then split. One signal will travel to the left, is amplified (this transistor has a variable supply current controlled by PWM supplied by the indoor unit), attenuated, frequency doubled, filtered again to get rid of the 6.XGHz signal, amplified twice and then reaches the Teledyne TBQ3018 30dbm Amplifier after wich the signal is fed into the coax to wave guide transition mounted in the die cast housing.

The signal traveling to the right after the split is fed into a PLL chip of which i could find absolutely no information. However it is operating at 128x prescaler. At 14GHz output that turns out to be a modest 109MHz of signal that the outdoor unit locks on to coming from the indoor unit.

The LM2941 i the upper left corner is the regulator of the final power stage and its current can be changed by the nearby potentiometer. Default bias is 600mA but im pretty sure it can be upped a bit without causing damage.

A little to the right there is a MMPQ2907A multi PNP used to control the bias current of the rf stages. The OPs next to it can be used to set the currents but so far i did not bother looking at this part as a constant bias and some bridges at the PNP did the job sufficiently and i dont eed remote power control. It shouldn't be difficult though if you prefer to do it the clean way.

[Amper]

Modifications to the Board

Now lets talk making this thing useful to us.

Since i dont really want to emulate all the signals coming from the indoor unit i decided to poke around a bit and look for places to hardwire. As the PLL circuit seems to be running all the time the only thing needed to transmit *something* is to apply bias to all of the rf stages.

WARNING: The way i did this is not the most elegant, if you are willing to invest time please look a bit deeper into the regulation and use the feedback OPs and shunts already on the board.

First i added a 1k Resistor pulling the signal going to the first amplifier after the signal split down to ground. This one seems to be the one used to control transmit power and while it is PWM controlled the original square signal would be filtered and smoothed anyways so just slightly pulling it to ground will result in the necessary bias to flow in transistor right next to the amplifier below the VCO.

Next is the supply to the frequency doubler. It can be done by bypassing the second from the bottom transistor in the Q8 PNP array i talked about earlier. Just solder a [Forgot the value,will add later] Resistor across and there will be sufficient current flowing. when operating at the original frequencies this supply will automatically activate once the 109mHz signal is applied so you may also modify some filter allowing to activate at our lower frequency but i haven't gotten around to this yet.

Third and last connect pin 1 and 16 of Q8 to apply power to the pre-amp next to the power stage. It seems not to need any regulation.

Supplying 15V to the module now should result in a current draw of roughly 500-600mA. Supplying this power and 109MHz sine though a bias T will turn on the final PA and raise the current to 1.2A indicating transmission.

IMPORTANT: When the shielding Block is removed the output will couple into the last filter and result in Oscillations of the entire Power section at 9-13GHz at significant power. While this will not damage the Hardware in my experience you now have a very wide band rogue transmitter that can cause all kinds trouble. I have no idea what users are next to the 3cm band but im pretty sure you could seriously piss off some authorities if you are unlucky. you are responsible to follow the law of your country, experiences may vary.

If you are so fortunate to have a suitable frequency counter or other equipment to deal with 14+GHz feel free to poke around and check if all is working accordingly. if you are still using the original VCO (wich you should not if you dont have a nice faraday cage lab) you should now be able to see 14GHz at the horn when 109MHz are applied.

VCO

Using the stock VCO in the big metal can will get you as low as some 13.8GHz which is useless for legal amateur operators.
As i dont like to get in trouble and at this frequency and power there can be significant range achieved (after all this thing is supposed to transmit to a geostationary satellite reliably at a distance of 150km atmosphere and 36000km (!) space) i had to get the frequency down into the 3cm band at 10-10.5GHz. As the device is using a frequency doubler this will require only a fairly simple VCO achieving 5-5.25GHz.

The HMC430 will fit this range perfectly and is also compatible with the 0-10V control signal used by the old VCO so nothing has to be modified here. It puts out 3db less then the od one but there is enough pay in the amplification of the system to compensate. The supply voltage has to be reduced from 5 to 3.3V. This should be done with a LDO but since i like to forget ordering things i just used two zeners and a resistor which works just fine at 30mA VCO supply current.

The old VCO is soldered down to the ground plane with its entire bottom surface so the only way of getting it out is hot air Doing this the shield cap will most likely fall off as well but we can reuse that later.

I deadbugged the HMC430 to the groundplane right next to the 50Ohm output Trace, added my makeshift 3v supply and after sprinkling some decoupling caps on top soldered the shielding lid to the ground plane covering my mess 

This mod turned out to work beautifully right from the get go, the PLL circuit seems to work without a problem.

The 128 prescaler will result in a needed reference signal of roughly 81.5MHz now to reach 10.430GHz HAM frequencies. My HP5350 confirmed this. since 80MHz is insideof the FM broadcast frequencies i plan on using a silabs Si4712 FM transmitter chip to generate this signal but so far the Fgen had to do the job.

Deadbugged HMC430:

[Amper]

Waveguidestuff

Now that i have a working 10GHz source i could start worrying about wave guides.

Luckily the LNB and Transmitters WG ports are WR75 by size and can deal with 10GHz beautifully. The horns have circular wave guides and will also work beautifully down to 10G. The worrying part is the splitter/ filter sitting in between. It consists of two halves bolted and glued together. Some are painted and the Bolt holes are plugged but i guess thats only a question of determination and maybe a blowtorch.

On the inside we find a Transition from circular to rectangular, square WG directly behind the horn flange. Then the Signal is split in its polarizations vertical is going 90° upwards through a corrugation filter and some impedance matching right into the LNB. Here we are very lucky, as the receive Frequency of the Hughes VSAT system is as low as 10.75GHz we are not far off and by my experiments this filter will work just fine for 10.4GHz.

The Transmit channel is a different story though. Im not sure what the loop is used for but the width is to small to fit the lower frequency. Since i didnt feel like milling sharp corners and its only the transmission channel i decided its worth a try just to bypass it. A saw and file will do this job in a few minutes cutting the rib to make a straight channel from circular to rectangular port at a depth of 7.5mm. This turned out to work beautifully and at least didnt show any larger power loss at the horn.

The next worry was tx power going directly to the LNB and potentially destroying it but attaching a modified LNB with power detector showed very nice polarization separation.

Halves of the divider/ filter with newly cut TX channel:

[Amper]

Power detection

This chapter is not really related to the Project itself but may be interesting for other experiments as well.

Since i dont own any test equipment for these frequencies except for the counter some compromises have to be made. In some cases it is very very useful to have a rough idea of radiated power. For this purpose a friend of mine made a small board a few years ago based on a Linear LTC5508 RF Power detector, a tn13 and a bunch of birdseed. it has a little LED bar graph showing power level and supplied from a small lithium cell its very small. Attaching a small antenna or WG to coax adapter you can wave it around in space and estimate radiation patterns and transmit power. The chip is rated from 0.3 to 7GHz but in my experience works fine even at over 10.

Since i have around 20 LNBs and i killed one or two in the process of understanding them i will turn one into a standalone rf detector as well just filling it with a new board and some kind of display i still have to choose.

The detector also fits a directional coupler very well making it possible to detect reflected power from the horn or measuring forward power with attenuation.

Obviously all measurements i can take with this at the moment are not absolute but maybe i will find a reference device at some point to calibrate the chip to the higher frequencies.

Detector mounted on a directional coupler:

[Amper]

The LNBs

Regarding the LNBs it seems to be another jackpot.
They are straight forward LNBs without intelligence running an oscillator in a metal can. It may be tuned by pressing in the housing at a certain spot but the amazing thing is, the local oscillator is running at 10GHz already generating a wonderful 430MHz signal from our 10.430GHz. The lower frequencies may get a bit annoying but pretty much all modern scanners should catch the legal ham frequencies this way. Just add a bias T and go for it.

In the future i may try to put an oven around the oscillator as they do have quite a bit of drift with temperature. Holding the LNB in your hand after having it sit at 20°C will require some tuning of the receiver for a few minutes. Maybe here is also some way to couple it to the transmitter or get some other crystal based reference in there but for now it fulfills my needs.

[Melt-O-Tronic]

Oooh, I can learn a lot from this!   

[0culus]

Very neat  This is exactly the kind of stuff I want to get into playing with.

[Amper]

Thanks ^^