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Hi
Hi
Everyone I know there the issue of Ramsey being not to legal power. I have been a engineer fro many communications Company… Ok I am going to tell you how to make the Ramsey kit really FCC Legal.
First of all take R34 and R33 out of the kit.. Your are going to replace them with a 50 ohm resistor or
two 100 ohm resistors parallel to equal 50 ohms..Ok put one end of the resistor where R34 is the closest to C23 ,and the other end goes where R33 is next to C18.
Next it best to have a Antenna load on your transmitter for alignment..I have a base loaded antenna.
Ok for alignment
The Bias adjustment needs to be set for 6.85 Volts now…. (note you need a 12volt soure,and I mean 12volts
regulated.)Finding your current to the Final stage.
Measure across the 50 ohm resistor and you should get 5.96 volts( under antenna load.)
That the resistor that replaced R34 and R33.5.96 volts / 50 ohms = 119.2 ma
Now measure from source to drain and the voltage should be around .84volts
I * E = P
119.2 ma * .84 volts = 100.1 mw DCinput power to final…
This will put you in compliance with the FCC rule for the 100mw power on final.
I really hope this helps alot of you out,and by the way my Ramsey AM25 Transmitter works great this way.
Thanks Retired Senior field communications engineer for Raytheon/US GOV.
Total posts : 45366Sean,
Thanks very much for the report. One of my concerns raised in the thread with Carl was that increasing R33 and R34 does not address the problem which I observed with the modulation coming from Q9. Have you checked the audio and maximum undistorted modulation percentage with this mod in place?
Neil
Total posts : 45366Yes I did check it.
If you turn up the pot that controls the line Audio input.. The Transmitter reaches near 100% modulation. As you mention before by increasing the DC input power the Modulation went down to 50%
from your 80%.. Well From what I can tell it running at 97% modulation right now and very clear.
Output sinewave is very clean. I still have not determined what the output power is,but it still seems
to put out a good signal. If I had to guess the transmitter outputing 25mw..That about 25% of the input power. Well Play with it and see what you come up with… Now the 12 volts really needs to be 12volts.
So if you have a variable voltage supply that regulated then that the best. Anyways it will not have that 60hz hum either like the cheap power supplies. I am going to try and find a AM broadcast Power meter that will
go down that low in power. All mine run from 1K all the way to 20KW. I have one 10 Watt meter made by
Lafayette. Now this is not a CB meter either. It runs from 1 Mhz to 30 Mhz. It has Power meter for 10 watt
scale and 100 watt scale. It has SWR reading,and Modulation reading. As well as a very sensitive Field
Strength Meter. It very old and are no longer sold. They were sold back in the 1960’s this one is still in Calibration. since the lowest reading on it is 100mw that does not help. it shows 100,200,300,400,500 mw
markings,but since we are running below 100mw output that will not register on this meter. Now a Oscope
is really the best way to determine the output watts. Again I am really thinking about going with a SSTRAN
Transmitter even though you can get the Ramsey down to 100mw input .I really think the SSTRAN 3000
give a higher output….. Has anyone done any test on the SSTRAN to see what the output power is????
I know it 100mw DCinput,but what the output power like. 50 mw would be good and that would at least
make the circuit 50% effecient. I know Ramsey is no where near that…For instance you said you had it at 194mw DCinput yet you only had an output of 32mw. Well a 25% effient circuit would put out 48mw with a
194mw DCinput. So really Ramsey is running less than 25% effiecent that terrible. Well What your thoughts
on that. That why I said the power may drop down to 15 to 20 mw output. I am just really hoping with the mods I made it puts out 25mw. Anyways that why I am really thinking about going with the SSTRAN 3000 since to get a good output on a Ramsey you have to run illegal power inputs. I think Ramsey could have taken more time and research to make a reall good part15 transmitter. I think like you do that this transmitter
was designed for higher power levels. Just look you can set it up for a 1 watt output signal for over seas,and if the truth be know that what it was designed for. I bet then Ramsey got the ideal well if we
stick R34 and R33 into this circuit it could be used for Part 15 too. Well they were so wrong since they have the input power almost up around 360mw or higher…That maybe also the reason the 100mw output power they claim the transmitter gets. The FCC rules does not say 100mw output power, so who thought this at Ramsey was out in left field. Anyways Ramsey can be made to meet the rule with good modulation,but with very low Transmission output power. Well have un with it. It works good on mine right now,and I can go out
over 300FT with a base loaded 10ft wire not even off the ground but 4FT. It may get out much further if the antenna was 10 or even 15ft high in the air. It make the Ramsey kit legal and the FCC cannot bust you.Thanks Sean
Total posts : 45366Sean,
Thanks for the interesting report. Your assessment of the audio with your modification is encouraging but I must ask if you observed the modulated waveform on a scope. OK if you didn’t but it would help me follow this. My measurements of the undistorted modulation percentage were made using a Hitachi V-152F analog scope and a calibrated eyeball. When I perceived distortion, I back down a bit on the audio and use the classic (A-B)/(A+B) equation from the scope measurements to determine the % modulation.
I would rather not get into ascribing motives to the Ramsey designers and prefer to just take the design as it is and it does appear that you and I have confirmed that there is a problem with the input power.
Regarding the SSTRAN, I have made no claims regarding the power output or efficiency since my only power measurement was the input power which has always been below the 100 mW limit. It may be unrealistic to expect that the efficiency will be better than the AM25 and it would be great to have real data to indicate otherwise.
Neil
Total posts : 45366Yes I did but it a real old scope. It show from 95 to 97 % modulation was clean.
Sean
Total posts : 45366Hi Neil
have you had a chance to run any test on your AM25 Transmitter with this new modification???
Sean
Total posts : 45366Hi Sean,
No, I haven’t though it sounds as if you did everything right. I like the AM25 except for the high power and low undistorted audio which is why mine is retired. Based on what you have reported, it is due another look.
Probably won’t happen soon, but I would like to replicate your experiment and if I do, I will post here.
Another complaint from users of the AM-25 has been that transistor Q9 runs very hot. Your mod should solve that problem also. Have you noticed a temperature difference before and after?
Neil
Total posts : 45366Hi Neil
Yes the transitor heat went down considerably…It runs luke warm now,and no longer hot.
That transistor really ran hot with a 300 to 400mw DC input to the Final..Really I don;t see how that
transmitter can put out a full watt with out blowing out the Audio transistor…I may guees it would be safe to have a 1 watt DC input to the final stage,buy you better heatsink that audio transister very heavy. Really large heat sink with blower fan on it too. Like they do to CPU Chips in Compters…I really thinkl if you set the transmitter up for 1 watt output that the audio transistor would short out due to thermal runaway..
I would really have to study the transmitter design and see how the 1 watt output could be done without blowing up the audio transitor. I did notice on the box that the transmitter bring up 9 volts.. Well maybe
when R34 and R33 are out of the circuit then a regulated 9 volt power supply should be used. Then
4.5 volts goes acorss the audio transistor and 4.5 volts goes accross the Final transistor. I thin 1 amp at 9 volt would work good… If the final drawed 1 amp at 4.5volt then that 4.5 watts DC input and if the circuit is around 25% effiecent then that 1 watt output. So I really think a 12volt power supply is to big when trying
for the 1 watt output..That 15volt power adapter would just blow the transmitter up in the one watt mode.
If it was me I would have a 9 Volt Regulated 1 amp power supply then the 1 watt output would work without
blowing the transmitter up. This is for all the people in Foriegn Countries who can run the one Watt. Try this
and see if it works for you. Neil you and I are stuck with 100mw DC input.. I would look for a design that
is at least 50% of the input power. I have a paper from the FCC that even says 100mw dc input and 50mw
output,so even they think 50%.
Ramsey is 25% or less they really need to work on the design. Talking Signs had the TS-100 AM transmitter,
but I have no ideal what their output power is like either. Rangemaster claims better than 90% but in my day of engineering there is no transistor circuits that good. A class AB push pull RF circuit the best hope for is 78% of the input power. Most circuits used by Radio Shack in CB’s is Class C bias and they get around 50%
input power. Well there you have it. I have made alot of my own Amateur Radio transmitters and that 50%
is hard to achieve so 90 + % out of a transmitter is hard to believe. If I bought a Rangemaster I would test
the input power then measure the output power… Rangemaster is a good transmitter,but I would definately
check that output power on a Watt meter or Oscope. Neil I am going to use the TS-100 since it is FCC Certified,and it has 100% mod and built in Antenna tuner like the SSTRAN 3000.
I am thinking about buying a SSTRAN 3000 For myself I have tried friends and it seems to work really good.
I like all the functions the SSTRAN has on it.Sean
Total posts : 45366Hi Neil
I looked it up in my engineering books. If you get a match pair of transistors NPN,PNP then a push pull
RF Circuit could deliver up to 78% of the input power…Well 100mw DC input and 78mw output now that
really good. I talked to the designer of the SSTRAN 3000 and he thinks his is around that 25% mark too..
I also saw a Stereo AM transmiter that said get 30mw output… Well I am guessing most the tramsmitters
are running 25% or just a little better..Maybe 30% tops. I am going to work on designing one that gets that 78% mark and then I will see from the FCC what I need to do to sell it legally. I know onw thing everone
uses magnet wire for their coils. Ok I have been into Crystal radio and contest. Winding your coils with Litz
type wire make really high Q coils and would produce a much higher output..It sure helps my Crystal radios
that I have designed and I placed 3rd in the world in a DX contest…I receiced hundreds of stations off a Crystal radio that were over 2000 miles away on the AM band. Some were only transmitting with 7.5 watts,and this was their test signal. Radio stations will test sometime before coming up with full power,so
if you know when they are doing that then you really can see how good your receiver is. I had a station last month that was over 100 miles away from me ask and see if I could get their test signal… Well their test
signal was 500 watts,but durring the day no skip. Well with no skip I was able to receive their signal pretty
good. Boy if we only had 500 watts to play with. The station then goes up to 2500watts full power.
That 7.5 watt signal goes back to the year 1928. There was a tube sold back in the 1920’s that put out 7.5 watts and everyone used it. Well this station still had that transmitter from back then. I even have the schematic for it. It amazinf because I have a book and there were hundreds of 7.5 watts stations in the 1920’s and 1930’s… Well enough of that back to the subject a 78mw RF output transmitter can be done
with only a 100mwDC input….That really would increase the range of getting out over 25mw or even 30mw
which most transmitters fall in this range somewhere. There may be a fe 50mw output transmitters out there
but I would check them with a watt meter before buying them. I would really want to see if they are putting out 50mw….Anyways Ramsey transmitters are putting out 100mw if you build them to the book,but remember one thing to get that kind of power they are putting close to 400mw DC input. This is far above
the FCC rules Part 15 limits…..My transmitter was running at 380mw DC input before I made it legal and that
was making the transmitter by the book and using a 12Volt regulated power supply. If you use that 15Volt
Power Adapter they send with the kit you are way over a 400mw DC input power and the FCC only allows
100mw DC input… This transmitter really could get you into a lot of trouble with the FCC if not changed.
Well Neil I will work on a push pull circuit that can produce 78% of the input power and that the best
anyone could do……I will look and see if Ramsey Design could be brought up to 50% too instead of the 25%
mark. There may be a way to improve on the design.Take Care Sean
Total posts : 45366Sean,
You have put a lot of thought into this and something good will result. Ermi Roos is a frequent poster here and during the past few years he has discussed efficiency of the final amplifiers, FETs, Tubes, Litz wire, coil Q and about every other thing which pertains to part 15 AM hardware.
One article he wrote discussed a problem with FETs as output devices but I couldn’t find it from a cursory search. Try using the search function on this site. Start with “efficiency” and you will get more than enough reading material to keep you occupied for a long time. There is a tremendous amount of technical material archived here.
You mentioned building your own transmitters. It has been many years since I built an AM transmitter and this was for a carrier current station. The input power was 25 watts but I never bothered to measure the output power since it “carried the mail” as intended and I wasn’t interested. Plus it was a class C tube design. More recently, I have built several class C VHF FM amplifiers for 2 meter ham use. Running in the 25 to 40 watt range with a single transistor I measured efficiencies near 70%.
I have to wonder if the AM-25 could not be modified to use a bipolar transistor instead of a FET and perhaps yield better efficiency. As you know, the AM-25 circuit lacks a tuned tank so a lot of power at the drain of the output transistor could just be wasted in harmonics. A tank tuned to dip with a link coupling may work a lot better. Just brainstorming here.
Neil
Total posts : 45366You are right.. I have a 1942 copy of the Amateur Radio hand book. In it it has many designs for transmitters
going up all the way to 800 watts output. I notice in all the Circuits it use two tubes in a push pull circuit
for the final output. I know that has to be to improve the input verses output power. I think with these low
power AM transmitters that a good push pull final amp would be great. Yes lets get back to Bipolar Transistors. A good NPN,and PNP matched bipolar set of transistors should produce a good output.
I notice when Changing my antenna that I had to rest the Bias on the Ramsey to keep the 100mw DC input,
so the adjustment of the Bias will have to be done on the antenna you are useing at the time.
Yes I forgot you did ham radio too. Do you do much on the HF band??? Or are you more VHF… I would
really like to do 6 meters with alot of power and see if DX could be done on that band. I can do the lower
HF bands too. Anyways it would be really cool to see if we could make cantact with each other over the radio.
I usually like making my own ham radios since it seems to be a lost art. Everyone is in yo buying Kenwood or
Yasue HF transmitters…Not me I make my own,and I can really get out on them too. I have really old tube
CRC-808 Rated at 200watts input and can put out 140watts by it self. I also have a 4CX1500 tube and that baby will put the watts out. Well let know if you would like to make contact sometime over the radio.Sean
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