Random Delusions
No one knows what this web site is about, or what its purpose is, its like the stonehenge of web pages.
Below is a design I came up with for what is called either a "DB4" antenna or a "bowtie antenna" for TV reception. This antenna is an excellent performer on the UHF frequencies.
TV is supposed to be free, and now that the networks are broadcasting in digtal, the picture quality is perfect HDTV. Why are we paying the satellite or cable people 100 bucks a month? Well if you can do without HBO, gve this a shot.
I bought a rabbit ears antenna WITH a pre-amp at the hardware store... and received ZERO watchable TV stations. The antenna I describe here, made for about $20 in parts receives 5 channels in our area almost perfectly.
Most of the designs I could find for this antenna style included a 7" whisker length, with no explanation as to where this measurement came from.
The UHF frequency allocation for television is about 470 to 890 MHZ, so the center of this band is 680mhz. A 680mhz 1/2 wavelength is about 8.7" long in free space, and so a copper element half wave dipole should be about 8.3 inches long. Not 7". So maybe this 7" number is a compromise to cover the VHF band as well??
The center of the VHF band is about 195mhz, which has a 1/4 wavelength of about 15.1". Multiply this by .95 to get a copper element length of 14.3". Half of 14.3 is 7.125, CLOSE to 7"! So nearest I can tell, a 7" whisker length looks to be about right for a 1/4 wave dipole antenna on the VHF band. So t looks like 7" is a nice compromise for an antenna to be resonant on two different bands.
Considering that most tv broadcasts on the UHF band, it would seem to make much more sense to me to tailor the antenna for UHF. And further, the antenna should be tailored to the specific broadcast frequencies in your area.
If you havent yet, be sure to check out http://www.tvfool.com/ . This is a great website that will tell you where the TV signals are coming from in your area, how strong they are, and what frequencies they are... all invaluable stuff for antenna design.
In my area, all of the broadcasts are clustered around 500 mhz, which has a 1/2 wavelength of 23.6". Halve that again, and multiply by .95 to get 11.2"... the ideal length of a copper element to a half wave dipole to recieve 500mhz. Granted, this is not a dipole we are building, but dipole math is easier, and more honestly I have no idea how the "bowtie" design should be calculated. To me it just looks like 4 dipoles with funky shaped elements stacked on top of one another, so thats the math I went with, and 11.2 inches they shall be!
To the left and above you can see the copper elements made from 10 guage wire at 11.2 inches long. And this antenna did indeed outperform a previous antenna that I made with 10" element lengths, a 20% increase in digital signal strenth to be exact. Proof I think that antenna effectiveness can be greatly improved by catering to a specific frequency... rather than trying to half ass the entire TV frequency spectrum.
The main structure of the antenna is plastic gutter drain. it cheap, and worked perfectly. The reflector is something called 'hardware cloth' strung across framing pieces from a window screen repair kit.
The pictures can explain he rest of the construction, but this bad boy receives about 77% digtal signal strength from repeaters about 17 miles away, and takes one analog station from marginal to nearly perfect. (Admittedly, lengthening the whiskers on this design did caus me to lose one analog station entirely that wasnt broadcasting near 500mhz... but it was being duplicated in digital anyway so no loss.)
To the left you can see a hideous prototype in the background that STILL vastly outperformed the antenna's that are available retail in our area.
Special credit mst be given to: http://m4antenna.eastmasonvilleweather.com/ this is a great site for TV antenna design, and you should check it out.
How to Diagnose Bad Finals in a CB Radio.
I couldnt find this information ANYWHERE on the web, and I had to learn it the hard way, I post this in case the following information can help you diagnose radio problems.
I had two Cobra model 25 CB radios, an LTD and an NW WX ST. Each had a similar poblem, they would turn on and receive perfectly fine.... however they would not transmit. When hooked up to a a watt meter, neither would show any power out.
The one difference between the two radios, is that one of them would SHOW transmit power on the built in meter, but regardless, neither one would show any power on an external watt meter. The radio that showed output o the built in meter would also actually transmit for a city block or so, but no more. These two broken radios sat on my shelf for months, and finally I decided to dig in.
Most of the web information I could find indicated bad or faulty final transistors for these symptoms, however I couldnt find any more information on how to diagnose this condition for sure. So here it is!
The first step is to go to youtube, or google something like "how to test a transistor" ( http://www.elexp.com/t_test.htm is a good link) You will see that a transistor, to be propery tested requires high tech equpiment to apply voltage, measure gain, etc... HOWEVER there is an easy way to test for the most common faults with a simple multimeter. Apparently, when CB finals go bad, they do so catostrophically... meaning they dont "sorta" work, they usually either comjpletely fail, or are fine. Which means 9 times out of ten, the simple voltmeter tests suit our purposes.
A transistor should test the same as if it were two diodes... continuity between base and collector should run one way and not the other, same with the base and the emitter. The emitter and the collector should have no continuity in either direction. A little more research and you will see how to test and verify that the current is running in the correct direction, but this step probably isnt necessary. You will also have to google the part number of the final in your radio to find a data sheet which will show you which lead is the base, which is the collector, and which is the emitter. On all of the ones I have seen, the base is on the side, not the middle.
By the way, the finals are the little flat three pronged things that are probably bolted to a heat sink near the back of the radio. You should have one of each of these:
To test the CB finals... you MUST remove them from the circuit. Just heat up the solder joints and bend
the prongs straight off of the board, no need to unbolt them from the chassis. On the radios I have, they
all tested fine in the circuit, or I guess its more proper to say that any faults in them were not apparent until
they were removed from the circuit.
Once I removed the final and driver transistors... I found one that failed the above test. No continuity
where there should have been. I looked up its part number on cbtricks.com ... found it on ebay for 4
bucks... replaced it... and voila! Working radio, now putting out 5 watts. Incidently this was the radio
which was not showing any power on the interal power meter. As a side note, you are supposed to use
heat sink compound when bolting in the new final.. Wikipedia informed me that almost any substance was a better heat conductor than air and that flouride was an excellent heat conductor.... so...I used toothpaste, it has worked so far.
On the other radio... the problem seemed to be the same. Same symptoms at least. However the finals tested fine. The problem in it was so simple it was embarassing. The center conductor to the antenna jack was not hooked up to anything! There was wire and capacitor running up to it.. but the solder joint had come loose. It was hard tor impossible to see anything wrong, but there was no connection when checked for continuity. I soldered a piece of wire into the circuit, and I was getting 5 watts out. Done. So apparently the CB's internal power meter reeceives readings somewhere AFTER the finals in the circuit board.
So, if your CB is lacking power out, AND the internal meter shows no power... suspect a bad final and proceed as above.
Hopefully the above information will help you diagnose and fix your own tranceiver poblems, and you have as much fun as I do figuring this suff out!
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Alinco DX-10 Radio Information
The Alinco DX-10 is a radio I recently picked up after a long wait. I havent found much information on these radios on the net, so I thought I would as some information that I have come across regarding this radio.
This radio is an alter ego of the Alinco DR-135, and before that the CRE-8900. These radios in turn seem to be evolved versions of the AT-555 and its genre. Interestingly enough, Alinco's web page does not list this radio in its product line. They list the DR-135 for the Russian market only, but not the DX-10. I suspect the reason behind this has something to do with the FCC. At any rate, these radios have resently begun to become available in the US... and they are not the exact same radio as the CRE-8900, i.e. some of the CRE-8900 mods out there are different with the DX-10.
SOFTWARE:
First off, the CRE-8900 software does work with the DX-10, and you can download it from bellscb.com. The cable works as well, and I have heard reports of some radios coming with the USB cable. To get the USB drivers to work in Windows 8 you need to install the drivers that come with the software download from Bellscb. The drivers are not mentioned or referenced.... but they are there in the folder if you look. Secondly the radio must be be supplied with power and be turned on before the software will talk to the radio. The software is a pain to use, but it does work, and it allows you to program custom frequency assignments to all 300 channels. If I get around to it I might upload the file I created for anyone interested, its very combersome to create as you have to manually enter each and every frequency by hand. It wont even let you do a cut and paste.
FREQUENCY MOD:
The frequency mod on this radio is painfully simple, and NOT the same as with the CRE-8900. To access the complete spectrum that the radio is capable of, you need to press and hold the FUNC and EMG and the turn on the radio while holding the two buttons. Once this is done, the radio will let you switch between band1 or band2 with the channel selector. Once you have chosen the desired band, press FUNC again and restart the radio.
The radio will restart, and cover the broader frequency.
One caveat to this though... without the software you cannot access both the 11 meter and 10 meter bands without resetting the radio using the above steps between bands. i.e. one band covers 10 meter, while the other covers 11 meter. With the software however, you can program the broad band to cover both 10 and 11 meters, and you wont have to go through these steps again.
AUTO SQUELCH:
Ever since I picked up an old HR-2510 with Auto Squelch, I am in love with this feature. All radios should have it. It really is a nice feature when you are driving by places that emit AM interference, and constantly adjusting the squelch annoys you.
Where is the auto squelch on this radio?? The CRE-8900 has it, but the DX-10 isnt advertised as having auto squelch. Why Alinco would remove this feature is beyond me... and heres how to get it back.
Turn off the radio, press and and hold FUNC and DW while turning on the radio. You will then have the option to enable auto squelch with the channel selector, press FUNC, and restart. Auto squelch will now always be enabled on the radio, and to use it, you press the center button (unlabeled) on the mic whiile in FM or AM mode. Voila... automatic squelch control.
PERFORMANCE:
This is a nice radio. The sound is a bit tinny perhaps, but the output power is quite decent. Somewhere around 20 watts. I talked to Japan and Belgium on 10 meters on the first day I hooked it up. And this was barefoot with a dipole in the attic!
The clarifier is odd... as it isnt a true clarifier. But it works fine once you get used to it.
There are way more features to this radio than I have yet to discover or figure out. I give it a two thumbs up... its small size alone makes this radio well worth the money.
I recently accidentally purchased a badass vintage Kenwood R-2000 off of E-bay. Yes, this does happen. Especially when you dont read the description carefully. The Radio was described as not working correctly when I bought it, however I didnt read the description and just placed a bid because the price was so good. At any rate, the problem that was described was that the radio frequency dial (VFO) did not work when the radio warmed up. When the radio arrived, it worked perfectly for me... until....
After having the radio on for about an hour, the frequency dial completley refused to tune UP in frequency. It would tune DOWN just fine, but turning the dial clockwise (up) either did nothing, or it tuned the frequency down. Later this problem continued to exist regardless of the temperature of the radio.
I of course searched the internet, and found others with this same problem in this same radio. Most of the proposed solutions were red herrings, and now knowing the problem and how simple the fix was, I will post the results here for others that may have this issue.
Most sites suggested cold solder joints, lint in the optical encoder, or spraying the pots with contact cleaner, tweaking the pots and returning them to their location, etc.... None of these worked for me.
A review of the service manual did show that VR1 and VR2 (located on the same little board as the optical encoder) were responsible for VFO adjustment. Although an oscilloscope was needed for the proper procedure.
When you open the radio, VR1 and VR2 are those little blue and white variable resistor pots with phillips head slots in the top of them (see picture). I have had these completely fail in other radios, so I know they are often the culprit when diagnosing old equipment problems.
Long story short, one of these VR pots had developed a dead spot. The fix was as simple as turning the VR with a screwdriver to a DIFFERENT SETTING. Keep it set as close as possible to where it belongs, otherwise it will screw something else up. But all I needed to do was to adjust the pot to a slightly different location. In this case, it was about 4 degrees off.
Use some trial and error, as some settings I adjusted to made the problem worse, or created different problems. Be sure to mark the existing setting with a sharpie so yo ucan go back to original spec if needed!
I sincerely hope this write up finds its way to someone else with this problem!
Below shows the VFO board after the knob is removed, and the assembly unbolted from the face plate. The two VR pots can be seen at the top left of the board, in my case the left VR was turned slightly clockwise to correct the problem.
