Saturday, August 22, 2009

1296 2W Amp Update

I got the 2 watt 1296 amplifier working Friday evening. I have had some problems with it when I was working on it. Let me give you a history before I go on.

The active device is a Motorola SML7008, which is known to work on 1296, but with slightly reduced RF output. This was aquired on eBay as a kit.

A couple weeks ago, I installed the circuit on an aluminum pallet ready to install in the enclosure that I planned on using. After it was assembled, I installed a couple of SMA connectors, connected it to a 20V Dell laptop power supply, terminated the input and put my power sensor on the output.

When I powered it up, the unit oscillated. I tried all of the usual fixes - conductive foam, etc... to no avail. The PC board that came with the kit used single sided material, with 2 mounting holes for the board and the active chip is flange mounted with 2 holes.

The fix was...I installed some flashing on the top side of the board, wrapped it around to the bottom, and screwed the board down against the flashing to the aluminum pallet. This is what eventually fixed the amp.

Now, when I was testing the amplifier earlier, I discovered the transverter power output was a tad bit low. This amplifier likes 10 milliwatts on the input for full output. I'm getting about 2 mW. The output spectrum isnt as clean as I'd like either, so I'm planning on building a 3 resonater filter and will place that on the output of the transverter, and a MMIC amplifier following that, to drive the 2 watt amplifier. I'm guessing the filter will have about 3 dB or so of loss, so the MMIC should work out just fine. I will probably be using a MSA-1105 for the active device. I still need to look up the device specs, gain, etc., but I believe it should work out. Once I get this done, I'll be packaging the thing up and will try some line of sight contacts with it using one of my 10 element yagi's. Of course I'll keep you posted as to how it comes along.

WSPR Beaconing

Along the same lines as PropnetPSK, I ran across another system that looks promising, WSPR. Pronounced "Whisper", and is an acronym for "Weak Signal Propagation Reporter". This is the kind of thing that looks quite interesting, so I downloaded it and installed and ran it for a couple of days.

This looks to be a great mode. It decodes signals up to about -29 dB below the noise floor, uploads the spots to a realtime database and plots them on a google map. Most stations run about a watt or two, with some running a couple hundred milliwatts. This is an USB digital mode. Bandwidth is a whopping 6 hz! It does not take much power to be heard.

There are stations on most of the HF bands, however most are concentrated on 30 meters. Again, I would like to see some activity on bands like 2 meters, as being the extremely weak signal properties of this mode, it would be beneficial in showing enhancements on the VHF bands. So far, I have not seen any activity on 2 meters.

Although this is an excellent mode, I dont have a good working antenna for 30 meters, so my transmitted signals are typically down about 15 dB from others on the band. Until more activity starts to show up on bands above 10 meters, my activity on this mode will be limited, I believe. This is a personal preference, I would operate more if I had a 30 meter hamstick, which I may end up getting at some point, but for now, I will probably keep beaconing on PropnetPSK.

Tuesday, August 18, 2009

10 GHz & Up Cumulative Contest Part 1

Part one of the 10 GHz & Up contest was August 15 & 16th, 2009. I operated Sunday for a couple of hours on Lake Erie along with WA3TTS and KB8VAO at grid EN91kt. I would have stayed all day like they did, but I was on call at work for 13 radio stations, so I cut it short, just in case.
Although I only operated from about 9AM - noon, I managed to work 10 stations. A large number of VE3's were roving across the lake, into Michigan and around to Ohio. Unfortunately, I did not work them all at every stop, as I left around noon.
Veteran microwave operator, KB8VAO operated the lake both Saturday & Sunday. I dont know how many QSO's he had, but I'm sure he did quite well, as the band was even better on Saturday than Sunday.
Mike, WA3TTS worked 20 QSO's on Sunday. He spent all day there, and this was his first time out on the lake operating with any real seriousness. Mike was up on the lake last year during a microwave activity day running a milliwatt or 2, but his receiver was confirmed working perfectly. Now that Mike has had a taste of some 10 GHz operation, I'm sure he will be quite active in the future. Mike is also planning on building a beacon for 1296 and 10 GHz.
This was a really fun event. It adds a new dimension when you get to operate with other microwaver's. Steve coordinated the operation because he was running the most power and was the most experienced among us. I have to thank Steve because if it wasnt for him, I dont believe we would have done as well as we have.
Now for the 2nd part of the contest, there is talk that Saturday, we operate from Lake Erie again, and from Blue Knob, a mountain in south central Pennsylvania. I have never done a mountaintop operation before, so I'm sure that will be an interesting operation. From what I hear, the long haul DX possibilities are nothing short of incredible, so I cant wait to do something from there. I went to the mountain last summer to check it out, but havent operated the mountain. You can see for miles in every direction, so no doubt, 10 GHz will go a long way from there.

Wednesday, August 12, 2009

Software Defined Radio

Something I've been playing around with, on and off over the past few months has been Software Defined Radio, or SDR for short. A few months ago, I ordered a kit receiver from Tony, KB9YIG. He has been continuing the "Softrock" series originally sold by the American QRP Club. The latest "Softrock 40's" currently are synthesized, and are controlled totally by computer. The theory is a bit deep as to how these work, but for simplicity, I'll say that the sound card in a computer does all of the demodulation of the signals.

This opens up a whole new world of radio. Here, a small pc board, which costs about $50 will tune the HF bands thru 6 meters, and do it so well, it rivals almost any radio on the market. The features of the radio is only limited by the software used in conjunction with it. Using this radio, and a program called "PowerSDR", the receiver will tune, general coverage from 1.6 MHz thru 30 MHz, or from 3.5 MHz thru 52 MHz. It will also receive all modes, USB, LSB, CW, AM, FM and DRM. Using external software, the receiver will receive all of the amateur digital modes (PSK, SSTV, Olivia, Hellscreiber, etc), and with Dream software, will also decode shortwave DRM Broadcasts.

Tonight, I listened to Radio Canada International for about an hour, running Dream, listening to their digital broadcast. They did a commentary, News, etc, which is what you would normally hear on a government operated shortwave station, but they also played some music - Gospel, Jazz, etc. I will say, the quality was almost as good as FM broadcast quality. Absolutely no noise whatsoever, and the frequency response and distortion were exceptionally great!

Of course, the receiver will listen to the analog AM broadcasts, as well as SSB and CW with no additional software.

The display shows a panoramic view of the frequency domain (It looks like a spectrum analyser), and by using different sound card sample rates, you can see anywhere between about 50 KHz to about 200 KHz of spectrum using 48K thru 192K sample rates respectively, provided your sound card is capable of the faster rates. I usually run the 48K rate, as the 96K rate my sound card sounds choppy.

Originally, I purchased this device as an aid to finding rain scatter signals on 10 GHz (with the appropriate converters), however, this is just so cool, that I have been using it as a general coverage receiver.

I just purchased a electronically switched bandpass filter kit for the input of the receiver. The way I have been using this so far has been by changing out little monoband filter boards that cover sections of the HF spectrum. The kits, including the bandpass filter are mostly surface mount devices, and the parts are extremely tiny. There are special techniques for building with these components. I'm finding my eyesight isnt as good as it used to be when I was younger, as I've been having trouble seeing what I'm doing. I can only work on it for about half an hour at a time till my eyes get "buggy".

The link to this really cool project can be found at
Hope you try one of these, you'll have a blast with it! They also make a version that transmits also.

Saturday, August 8, 2009

Absorptive SWR Bridge for the Microwave Bands

A number of years ago, I built an antenna tuner with a very simple SWR meter built in. This SWR meter worked using the Wheatstone Bridge theory, and the indicator was an LED. This meter worked well on HF using 2 watt transmitters. It had occured that since most microwave work is at similar power levels, why one of these meters wouldnt work on VHF and above.

I therefore built a meter similar to the one I used. I found an article on W1GHZ's site, that was very similar to what I was using. Here I thought this was a new idea for a microwave reflectometer, but Paul thought about it before me. I did, however use his circuit, and I also made a few modifications to his circuit to make it better. The schematic is shown. Click on the image for a larger view.
Basically, this is a wheatstone bridge. The three 50 ohm resistors, along with the output port, which if the impedance equals 50 j0 ohms, there will be a null across the 100 ohm resistor, and therefore no diode current. If however, the resistance is anything other than 50 ohms, an imbalance occurs, and RF will be present across the 100 ohm resistor, as well as across the diode. The imbalance current is read on the meter, and can be calibrated as SWR. One feature that is inherent with this type of meter is that it always presents a load near 50 ohms to the source, preventing any kind of burnout of the PA. The disadvantage of this type of circuit is that it cannot be left in the circuit, as it will have approximately a 6 dB loss.

The resistor with the "*" can be found experimentally, or replaced with a potentiometer of about 10 K or so to adjust the meter for a full scale reading with no load connected. To measure forward power to calibrate the meter, remove the antenna or output connection. To measure reflected, simply reconnect the antenna or device being measured. The power handling of this device is quite low, so don't transmit into the meter running more than a couple of watts for very long. My meter will calibrate with 1 watt applied. This meter will work using standard leaded resistors and chip capacitors up thru 432 MHz. To make the unit null on 902 MHz and above (probably thru 2304), you must replace all the resistors with chip resistors. Remember, any path carrying RF should be made with 50 ohm stripline.

My present meter is using the standard metal film leaded resistors, and the null is very good on 432 mhz. I use sma connectors for the guzinta and the guzoutta. I used what I had available as far as the resistors and caps are concerned. I have leaded resistors but no leaded caps, so I used all chip caps for mine.

This device can be used from HF - SHF, but it is a QRP meter. I wouldnt load more than 5 watts into this device.

If you have any questions on this meter, please leave a comment. I will try to answer any questions you may have. I hope that some of you may find this device useful, as it makes antenna tuneup easy, and protects the final of your radio while youre tuning!

Monday, August 3, 2009

1296 amp, and other things....

Today I built up my 2 watt amplifier for 1296 (23 cm). Basically, the board was built, I just mounted it to an aluminum pallet and built a small brass enclosure, mounted sma connectors and power connection.

I tested the thing out using a reduced voltage. I hit it with 12 volts, the unit takes 20 - 24 volts. Turns out it needs like 15 - 16 volts for it to start working, and of course, I had nothing coming out. A phone call to Mike, WA3TTS confirmed that I needed more voltage. I have a couple of old Dell laptop power supplies that are good for about 20 volts at 2 - 3 amps, which should work ok running this amp, which I will use. I will set that up another day, because I need to make this idiot proof, cuz....well, lets say, I've been known to be an idiot sometimes! ha ha... Dont need 20 volts on the transverter or the IF radio.

I also installed Windows XP on my shack pc. It had Vista in it, and I found that my software defined radio did not work in Vista, and besides, this computer is REALLY slow running Vista. Now everything is working again. Just set up Propnet-PSK again, but I have it set up as a lurker station on 10 meters. I'll get the PTT RS-232 working in the next day or 2.

I also volunteered to help out with a local public service event here in New Middletown tomorrow (tuesday). Theyre having a village "party" at the village park, and it kicks off with a parade. I'm to help organize the parade and provide communications for the parade. I did this last year too. Its one reason amateur radio exists, to provide communications as a public service. I therefore am helping to justify our frequencies by helping out in local events.

Well, I havent been doing that much radio wise lately, as the blog shows. The 1296 rig is still my current project, but its time to start packaging the rig, and putting the system together. Once the 2 watt amp is working, then I'll need to rebuild my 30 watt amplifier, then we'll be pretty well set up. Of course I'll keep you posted! 73 for now...
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