Is anyone familiar with "direct" and "indirect" power readings of AM transmitters, specifically for the SSTRAN transmitters? I'm curious of how to do this and what equipment is recommended. Presumably use a volt/ohm meter.
I'm not an engineer, so keep it simple if you can help.
I am interested in keeping a log much like the FCC would require of a broadcast station and need to figure out how to read the power and calibrate equipment.
KDX-FM transmits from a Ramsey FM30b transmitter which until yesterday shared space on an indoor bamboo tripod tower located about 4-feet behind the operator position in the master control room.
The bamboo tripod currently hangs the receiving antenna for the station's Lectronics Wireless Mocrophone.
The new KDX-FM transmitter location shares an audio line from the SSTran AMT3000 KDX-AM transmitter alongside the legendary "Wintenna", a metal window frame serving as a portion of a 3-meter vertical antenna facing in and out doors.
The KDX-FM telescopic vertical antenna is about 15-feet from the control area and because of the adjacent window is expected to better serve a portion of the campus outside the building.
I don't recall seeing this transmitter review linked, so let's have it now!
Was on kajiji and came across someone selling a Decade MS-100 here in Toronto(older model in plastic case) and only wanted $80 for it so I went to see and was cosmetically like new and operated perfectly also so I grabbed it.....brought it home and was as good as a new one for the great price of $80! A good find I think.
There's a couple on Ebay now and they are asking for $400 CAN for the same one!
Thought I'd share that.
Mark
Sending one audio chain to three different kinds of transmitter poses challenges for the audio bandwidth.
FM transmitters handle the widest audio bandwidth with a response of 20 to 15 kHz (the high frequencies are rolled off above 15 kHz to avoid collision with the 19 kHz stereo pilot frequency but mono FM allows unlimited high frequency response).
AM transmitters face a channel width of 10 kHz but the audio pass is only 50% of this because both positive and negative swings of a 5 kHz signal add up to 10 kHz. Don't be confused, I believe with NRSC pre-emphasis sone stations are allowed to occupy 20kHz for a total audio response of 10kHz on a wide-band radio receiver.
Streamitters (Internet Radio Stream Servers) are a whole other breed with audio quality governed by bit and sample rates, which may or may not comply with AM FM audio bandwidths.
This whole ball of mess came to KDX Worldround Radio based on two recent experiences:
Wearing a DXer hat we tuned around the AM dial to observe which stations splashed into adjacent channels, suggesting wide-bandwidth transmission, and came upon one that was so tightly confined to its channel that I was able to hear a far off station on an adjacent channel without any splashover from the local. I was impressed and set my audio bandwidth to exactly 5 kHz and being a voice talk radio station it sounded alright on our FM channel as well.
No doubt music stations need as wide an audio band pass as they can get, but we carry little music.
Complications arose the day KDX decided to serve the most under-served audience in the world, a growing population suffering under slow internet service brought on by the skyrocket costs and inadequate service outside of major cities also to mention slow computers and a reviving interest in dial-up modems.
Enter KDX ONLINE 8 kbps 8 kHz.
At first we experienced heavy crackling ond poping because such low stream rates cannot transpose the upper part of the audio band, but some careful tweaking inside Stereo Tools Audio Processing software has somehow smoothed everything to the point where it all works.
If things work don't do anything else.
Part 15 Replaces a Lot of Wire
KDX Worldround Radio looked at the cost of wiring compared to the cost of air. Wire is very expensive and air is free.
That's why our station audio monitoring is done by FM radio and campus coverage is accomplished with AM radio.
"Look at all this air", said Fred Richter, chief engineer. "It replaces itself and there's no expense".
In setting all the power levels for the transmitters KDX looks to FCC Rule 15.15c -- The parties responsible for equipment compliance are encouraged to employ the minimum field strength necessary for communications.
The signals of KDX are the most challenging in the world for DX listeners, because we try not to be heard beyond our premises.
- RePrinted from ALPB Forums by permission of me
I built a class e tx, showed the 2n7000 about 22 ohms and used an L match to transform it to 50, throttled it back to 70mw using a resistor between lm386 output and inductor. Works great, but I'm thinking after punching numbers in the calculator, at 6 volts, at 80 mW, I'm looking at 142 ohms, this next build I'm inclined to lose the L match, and from what I've read, higher imp antennas are more efficient. Any thoughts?
| Attachment | Size |
|---|---|
 shortwavetx.gif | 5.83 KB |
Hi,
I have read that some of you are into shortwave broadcasting - in the 13.56Mhz frequency. Also some of you have bought a ready to use transmitter from turkey.
A few of the transmitters seemed to have trouble, also they are relatively expeinsve - but therefore ready to use.
However, for those of you who want to built their own shortwave transmitter I have a little project here.
It is a simple transmitter that I designed - made it as simple as possible. It consists of all parts needed for making a small shortwave station
- Oscillator and pA (both done by one transistor)
- Lowpass filter and match network for 50Ohms on the output
- AM modulator with audio amplifier for low level (headphone) levels
- Audio deemphasis to lower higher AF frequencies to keep the transmitters
bandwidth small.
The transmitter does generate a relatively good modulation - altough - you can tell by the simplicity of the design it is not comparable to a "full" transmitter with an own final amplifier and a proper modulation stage. I have made critical modulation tests and it does go very loud (means that you can
already hear the modulation as soon as parts of the carrier are beeing received) but over all the sound is kinda tiny. Hard to describe. It definately
sounds OK for a small shortwave station, speech and music are transmitted undistorted and clear (if you don´t push the modulation depth to it´s limits) but over all it does not sound as ... "strong" as a transmitter with a proper modulation stage and the capability to make >100% AM. I have very high test
intentions, so for a DIY circuit it´s allright, but not for a wannabe professionall transmitter.
I have neither tested the range nor measured the output power. All I know is that it is probably within the 10mW or less power range - since I orientated me on the knowledge that it seemed to be allowed to transmitt with 5mW into a lambda 1/2 dipole. With a 5 ft long wire antenna connected to the output from the transmitter without any additional matching (eg PI filter) it does generate a strong enough signal for every position in my room even when using a short antenna on the receiver and attentuator activated.
The transmitter´s output power can be regulated by varying the input voltage. It will work also with 9V - providing less output power - and it will also work with 24V (at least I tested it) but the modulation is getting rather quiet / eventually distorted. It has been optimized for 12V operation as you
may have a 12V power supply handy.
The frequency can be adjusted exactly to 13.56Mhz using a trimmer capacitor instead of the fixed 18pF capacitor. The capacitor 1nF in the modulator stage
between collector and base reduces higher audio frequencies - making the bandwidth that the transmitter requires smaller. 1nF is still a littlbe bit low, and the transmitter can still transmitt rather high audio frequencies relatively well. If you increase the capacitors value, higher frequencies will be supressed better.
If you power this transmitter with a "wall wart" power supply and have problems with hum you can try to increase the 220µF capacitor to 1000µF - altough 220µF should by far more than enough considering the power requirements of the circuit. If the replaced capacitor doesn´t fix the hum issue, add some 22µH inductors in series with the power supply (+ / -) and the audio source to the transmitter. Then add a wire as "ground" for the antenna to the transmitter - it will increase range aggain then.
Powering the transmitter with a DIY power supply AC to DC power supply it will work if you ad .01µF (10nF) capacitors parallel to the diodes that convert the AC voltage to DC.
The parts can be bought in most electronic shops. As circuit board a board with 5 times 10cm was used. Parts of it got cut out as seen on the picture and glued on top of the circuit board. There´s even lots of space left for adding a battery or using the space for own additional projects.
This is not a perfect instruction how to re built the transmitter - I´ve done some where I´ve put ways more effort into. The only thing is, I sit in front of my laptop, create drawings / pictures for hours and sadly had often the experience that it did not get worshipped by people in the way I wanted it to be. On a vintage radio collector forum they asked about AM modulator - can anyone make an AM modulator circuit that uses simple parts... I made one, does use some transistors covers all am band, and I showed it... They didn´t really pay attention to that.
I do not know - have low expections - how circuits are rebuilt here, so I just gave it an attempt...
(I am not sure if there is a picture because when I click on upload nothing happens, no feedback wheter the transmitter picture is uploaded or not)
On another Part 15 site a poster was lamenting that a used certified transmitter he had purchased came with a 1710 crystal but no instructions about the rules regarding operation on 1710 kHz. The speed limit on many interstate highways is 70 mph. Should the car manufacturers furnish instructions about driving faster than 70?
What Makes the Best Transmission Line
For an asymetrical dipole antenna, is the best transmission line a
1.) Shielded coaxial cable?
2.) A twisted pair?
3.) A lamp cord?
SStran, makers of the AMT3000 and AMT5000 AM transmitter kits, has announced they are not accepting new orders and are not able to fill their backlog of orders.
Since installing our EDM FM Transmitter, exactly like the one Tim in Bovey reviewed, set at minimum RF output power with a 1/4-wavelength horizontal Decade GPL32 dipole antenna, we've intended to make field strength measurements around the campus and today was the day.
The time was 11:30 AM, a TECSUN PL-310 with dBu/SN readings was the test instrument, its antenna open to 4-sections for a length of 13" always aligned horizontally on the same plane as the transmission, held at about 5' from the ground.
These numbers form a map of our grounds, all outdoors, X marks the transmitter, the top of the list is NORTH.
00/00 01/02 01/03
--/-- 00/02 --/--
--/-- 18/19 07/07
36/34 25/28 20/22
27/26 --/-- --/--
35/31 --/-- 27/30
40/31 --X-- --/--
52/41 53/49 43/43
--/-- 48/41
--/-- 42/31
--/-- 23/24
--/-- 05/06
The clear reception area on this radio is less than 100'.
The same clear reception area is observed on the auto radio in the driveway.
Weak spotty reception is detected on the auto radio in every direction for no more than 600-feet.
In the ordinary course of events many of our hobbyists would like to sometimes experiment with greater RF power or longer antennas than the part 15 rules permit, so as to make scientific observations before returning to legal operation.
It has generally been held that such "out of bounds" tinkering is not allowed.
I happen to be in that very position as at this time as tests are being run on the performance of Ramsey FM30b and EDM FM transmitters using Decade GPL32 Horizontal Dipole antennas and so far have been dabbling with small power manipulation amounting to a few feet of coverage difference.
As one final jab it would be fascinating to learn what these transmitter would do at their maximum possible power, but we are obedient to the rules despite complete disrespect for the Commission Chairman.
Perhaps a rare window of opportunity opens on Friday when government funding may end, at which time the federal government "shuts down". Or, there may be a last minute extension of time to December 22 when the government might shut down.
Duriing such a shutdown the government's rule making authority is suspended, no?
Operating on that rare human faculty known as "common sense", KDX will consider full throttle transmitter testing during any "shut down".
Until such time a comment period is open during which your thoughts are welcome.
Can't decide what transmitter to buy talking house ccrane or whole house transmitter which one would give more range thanks
Any one every heard of this one I found on wallmart but it it sales other places it says it gos 300 feet
http://www.hamiltonbuhl.com/store/products/1001/HamiltonBuhl-Additional-...
A fellow part 15 hobbyist asked an interesting question... he wanted to know a cross street where he could tune to KDX while he was in the area.
As it turns out KDX is not receivable at any cross streets because of the way I practice the hobby.
Neither my AM nor FM signals leave the property where I run these stations as a way of bringing myself good programming, and the signals do not reach the surrounding neighborhoods as I have no obligation to serve strangers, except in case of national disastor in which I have spare sardines to hand out.
Anyone know of good sources for schematics - specifically transmitters, but other equipment like diy compression, etc? Book sources are good too as some of the online stuff I was able to dredge up seems repetitive.
Hi all,
Long time Part 15 enthusiast and lurker here... I am using a Drake FMC-1000 FM Stereo Modulator for property-wide (personal use) rebroadcasts of streaming music, audio from my shortwave SDR and police scanner. The Drake has nice clean audio but the RF output is only just a tad above 1mW (+50dBmV @ 75 ohms). I am currently using a 1/2 wave vertical dipole fed with about 15 ft of RG-6 coax.
My issue is I need a bit more coverage of my semi-rural property. While still within line of sight of the antenna the signal fades a bit here and there. Of course these are areas I frequent most often. It isn't frequency related because I have tried multiple vacant frequencies across the band with the same result and it doesn't appear to be multi-path cancelation either. I am fortunate to have 7-10 good vacant frequency choices. I'm looking to add an additional 100 feet or so of coverage.
My choices seem to be 1) improve the antenna or 2) get a higher output transmitter.
Option 1 is limited due to the potential mounting options available. Using a Yagi or other directional antenna isn't a total solution since the low signal spots are not in the same direction. I may be able to add a few extra feet to the antenna elevation but that is also limited.
Option 2 is more expensive but a possibility since I used this transmitter so often and is of value to me.
Any recommendations for me for either option? Thanks!