Jump to content

Recommended Posts

Thank you so much Thomas,

It is your commments that I have been wanting to hear for a long time. It is so hard to learn this stuff and when people locally tell me everything is ok, and then I believe them, it does not help. However, the only way I can really learn is to have someone point out the deficiencies and what can be improved upon. If you lived closer I'd offer you free beer and my sister for the chance to pick your brain! :)

Thanks again, your comments are truly welcomed and appreciated!


Ps here is the instruction paper that came with the circuit board I used. I called them (DEM) and they said to use the same values for the module I have.


Edited by dalbert02
Link to post
Share on other sites
  • Replies 63
  • Created
  • Last Reply

Top Posters In This Topic

great !

see the amp come in many different versions for different frequency bands,

note how they explain how to connect to the end of in/out stripline,

this is even important at 50Mhz.

I would have made the case design so the center pin of connector would fit directly on end of stripline,

and the low pass filter is SUPER important ,

but the frequency is your luck ! 50x2 = 100 check with normal FM radio,

find a weak station near 100Mhz, and setup your transmitter with antenna and all,

use exactly halve the FM radio frequency, and see if you have any harmonic problems,

I bet you will prevent anyone in whole miami from listhing to FM stations from outside the city, if you have no low pass filter attached.

the 3x harmonic is often evnen stronger on some amp types,

150Mhz is a puplic band, companyes pay to use those frequencies for cars and taxi and police and such, so extra care and testing is important,

most radioamateur handhelds will cover this band also in listen mode,

so you can check, or got access to a scanner ?

the best way is if you can rent or borrow a real spectrumanalyzer ?

many ham radio freaks have one of the old types, or know someone that got access to one,

Edited by ThomasScherrer
Link to post
Share on other sites

I will check for harmonics. I have a Yaseu VX-7R handheld that will tune above and below my center frequency in 10khz increments then tune in on the even and odd order harmonic frequencies. Is it posssible the amp module has circuitry to attenuate the harmonics? I took the amp to work where we have an Aeroflex IFR 2975 service montitor. Attached is a pic of the just the carrier, the ppm signal was removed. Next time I go to work, I'll take a pic showing more spectrum, I can go from DC to 2.7Ghz. I don't always work at the same location, so sometimes a number of days go by before I get to the location with the radio test equipment. :(

On to your suggestions:

the decoupling powersupply to amp, use 180pF 0805 size

and two in parallel, on each input to GND, and where the caps are GND connected Is this your recommendation for my amp or for your filter design?

this design will radiate power almost as much on the power line as on the antenna :-) My amp or your filter?

electrolyte type capacitors near poweramps are useless in general,

ceramic types MUCH beter, but DONT parallel several different types, like 100pF 1nF and 100nF like I have seen done too many times before,

you will make resonant circuit with tons of hi impedance results, So, with my amp module, they have done exactly this, in the directions you can see I have several caps in parallel, an electrolytic and two ceramic SMDs. Is this a bad design, in your opinion?

Thanks again for all your suggestions, I truly appreciate them.



Edited by dalbert02
Link to post
Share on other sites

it is OK and good idea to parallel electrolytes with ceramics exactly like you did,

so that is fine.

I said it is BAD idea to parallel ceramics with different values

you did not do that fault.

the values of caps I said was for 450Mhz not 50Mhz !

Decoupling caps for 50MHz

0805 size 2.2nF

1206 size 2.2nF

always use NP0 or C0G types for RF

I find it wierd that you cant hear or see the harmonics with the VX7R

try wide FM mode ?

and try to adjust the 50Mhz carrier frequency, or add modulation and see.

those amps have no harmonics filter, sorry.

to avoid the powerwires from radiating rf, you need pi type filters,

and ferritebead filters and double decoublings, but if you dont see it as a problem, then dont worry,

I dont know if you have a radio amateur license class ?

in case of interreferience or jamming stuff the license will help you,

it will almost grant you imunity to confiscating of equipment and huge fees to pay in case of illegal harmonics. actually if problems they will/must help you to solve it nice and friendly.

also I bet 50MHz is not for RC use, but for ham radio :-)

from 50-52Mhz it is reserved, right

low pass filter for 50Mhz:

180nH - 200nH - 180nH

62pF - 100pF - 100pF - 62pF

all caps to gnd, all coils in series,

start with cap to gnd, end with cap to gnd,

if you use short tracks and the 3 coils are 90 degree rotated or wall between them,

you will get :

0.1dB loss at 50Mhz

40dB loss at 100Mhz

60dB loss at 150Mhz

all caps 0805 or 1206 NPO, if you have 10pF values also, add 10pF to the 100pF

so you get 110 pF there, this will improve match, and hi freq kill also.

Edited by ThomasScherrer
Link to post
Share on other sites

I was editing my post when you replied. I did not hear anything on the harmonics but figured I would re-do my test in case I did something wrong and repost.

I still don't understand the capacitor issue. You say, "I said it is BAD idea to parallel ceramics with different values you did not do that fault." But I did do that. In the diagram above I have C3 a 0.1uF ceramic SMD, C4 a 1000pF ceramic SMD, and C1 a 2.2uF electrolytic all are in parallel.

I do have my technicians license, KI4HVT, but to be honest, the test was very easy and only tested very basic electronics knowledge. I don't recall any rf questions except converting wavelength to frequency. I have some ARRL books but in my opinion the example projects do not go into enough detail into the 'whys' of how things are done. It is from people like you, that 'elmer' me, that I learn the most. :)

I will continue to follow your advice and post results.

Many thanks.


Link to post
Share on other sites

AMA 50 MHz Amateur Frequency Band

Channel Number Frequency (MHz)

01 50.820

02 50.840

03 50.860

04 50.880

05 50.900

06 50.920

07 50.940

08 50.960

09 50.980

Granted I am only allowed 1W output, but in case of an emergency and need extra power, then the amp will be turned on. I would like to do what you have done and have a selector switch at 500mW normal, 1W long range and 10W emergency. For the few seconds I would be over powered to turn the plane around, I doubt I would be reported. Even at 1W I am more then 10X more power then stock transmitter.


Link to post
Share on other sites

ok great I look forward to see your updated pictures.

meanwhile a quest for you:


this is a picture of me, note the background ?


this one is taken 3 sec before, recon anything ?

then paralleling two or more ceramic capacitors of different value in a DECOUBLING voltage application, special care must be taken !

please read about internal resonalt frequency of each capacitor,

why ?? they are infact not only a capacitor, but also a coil in series,

ok it is darn little, but it IS there..

ok now I try with picture explain:


ok lets look at the circuit with TWO capacitors.


this is how capacitors actually work.


and more in parallel, uha see the problems ?

Edited by ThomasScherrer
Link to post
Share on other sites

The McArthure Causeway coming from Miami's South Beach! Ah, I wish I knew you when you were here! Are you ever coming back this way? I certainly owe you a beer! Thanks for the pictures, I will study them. BTW, do you have any opinion on this low pass filter?





Edited by dalbert02
Link to post
Share on other sites

yes I am returning to florida, we plan a new tour in 2010 allready,

this time mostly orlando area to visit all the parks with kids.

last time I won the trip on national radio, was all over florida with my wife for 14 days.

that filter looks really cool ! it is special designed for ultra low loss

and quite hi power !

you only need a 10-20W capable filter, so minispring coils and smd caps will be fine for you.

Link to post
Share on other sites


see how the new added cap change a few other values,

but really improve filter.

-0.1dB from 48-57MHz

-60 to -90dB on 100MHz depending on how accurate you can hit the resonant peak, for that you need access to network analyzer and adjustable air coils,

else I know you wil miss it, the tolerance of components and the way filters are assembled always dont match the simulated values/curves,

but with right measurement equip this can be fixed.

Link to post
Share on other sites

Well I tested my amp using my antenna analyzer as a source. I punched in 50.350Mhz and sure enough when using an actual antenna rather then a dummy load I swamped out the local radio station 100.7 in every radio in the house. I will definitely put it back on the analyzer at work and look at a larger spectrum to see where my harmonics are. Attached is a pic of me trying to make air core inductors. The slightest movement and the value changes, :(



Link to post
Share on other sites

Wow, You kids are doing exactly what I want to do, I am going to take my VEC for technician sat morning and was going to order a futaba 12FG 2.4Ghz FASST system but have been wavering about going a 50mhz rig instead and having an emergency amps just has been discussed here and from my reading of the regulations about emergency conditions it can be justified and used legally when the only other alternative is a loss of control of the model and possibly injury to people or property if that occurs.

So even though the 50 Mhz version will take a few days longer to get here I think I will change my order now as I should have my call letters shortly and the competition for frequencies is a LOT less at 50mhz and the power issue + the range is farther and as VHF television goes away next year in the states the band should quiet(i believe 1 US channel is about 50mhz. The same cannot be said for 2.4GHz ambient radiation :(

gwen hastings

Link to post
Share on other sites

oh another radioamateur cool !

ya sure you can make a 1-10W 50MHz RC system,

this lower VHF frequency will give you RANGE like no 2.4GHz RC system will do legally :-)

I use 434MHZ for RC and 0.1W is my normal power = plenty of range !!

I can pump it up in 5 steps, after my need for range.

>and sure enough when using an actual antenna rather then a dummy load

>I swamped out the local radio station 100.7 in every radio in the house

yes ofcourse I wanted you to use an antenna hehe not dummyload

by the way, you also jammed all the other FM radioes in halve of the city,

this is what makes 50MHz a big challenge to work with.

I suggest dropping the homemade coil you made,

you use too thinn wire, and too big a winding diameter and it is as you found out critical ! and big diameter radiate much more, not what you want in this case,

much better to log onto coilcraft.com look for "minispring" they handle 4A so good for kW if needed. they are really accurate and tiny, you will get a filter that is reproduceable for your self and others with documentation,

no need for others that follow you to invent the wheel again,

just put your construction online and tell what coils and caps you used,

and please rotate the coils as seen on the other construction there,

and keep 1/3" distance from coil to coil, then it will be real good.

Link to post
Share on other sites

I started to implement the mods you suggested. First I removed the old coax and put in some Harbour Industries MilSpec cable, M17/152-00001 Harbour Industries Then I removed the excess traces. Next I reinstalled the new cable as short as I could manage. Finally, I put everything back together and installed a ferite ring on the power leads. On the o'scope, the wave still looks very clean, but since I am home, I can't put it on the spectrum analyzer till next week sometime.



Link to post
Share on other sites

Oh yeah, I forgot to mention. I tried ordering a sample from CoilCraft but they rejected me!

Coilcraft's policy is to provide free evaluation samples to professional

engineers who are designing commercial products that will be manufactured

in volume.

We have searched the internet, but can find no information that shows

that your request meets those criteria. If we're mistaken, please respond to this

message with a bit more information about your company and your application

and we'll be glad to reconsider your request.

Being impatient, that is when I tried 'rolling' my own. I will order a few 144-06J12SL coils and related caps from Mouser this afternoon...


Link to post
Share on other sites

darn this is where the Kool kids hang out... count me in!!!

hope I can contribute technically very shortly...

very warm regards,

gwen hastings - researcher

ps we now return you to your regular noise level(s) after a fanboy has visited :)

(although S/N ratio is 1000/1 in this thread except for my own postings)

(humm I better pick up that 1/kw dummy load for 62.00 at HSC tonite or make my own out of a 200W power resistor, 4 quarts of silicone motor oil and a 1 gallon paint can + a couple of bits of wire to make a tank circuit :)

Link to post
Share on other sites

oh poor you hehe.. ok I did not think of that sorry.

but I guess Mouser/digikey/farnell also sell those cool minispring coils

or some that are similar.

How will you encode and decode the RC pulse ?

PPM or digital mode ?

and yes the design lookg much better now ? measured more power now ?

or no visible change ?

YO Gwen, please fill in your location in your profile ?

so we can see where you are from.

Edited by ThomasScherrer
Link to post
Share on other sites

Hi Gwen, and welcome to the RC-CAM forum. As you may have noticed, there are those on this board that help (Daniel, Terry, Thomas S., Thomas B. aka Mr.RC-CAM, etc) with their vast knowledge and then there are people like me who just ask a lot of questions and fumble around. Anything you can contribute is greatly appreciated. Suggestions and criticisms are certainly welcome.

My apologies to Thomas S. as I think I may have inadvertenly hi-jacked his thread. My goal was only to point out that although his amp is very superior, it is also beyond the capabilities of rf newbies like me. So, I offered my simple, lower power solution (-6db). In return I recieved valuable advice and hints that has fueled my hunger to learn more.

Nothing new on my amp over the night. I just read some ARRL books trying understand the multi capacitor issue above. It would seem to me after reading about capacitance and inductance that every little part of the circuit has an effect on the over all performance. What I mean is that there are parts of the circuit that are not designed but still exits and can cause an effect. Each trace on the board is separated by a distance which then acts as a capacitor and therefor may have an effect on the 'tuning' of the circuit. Even the board ever so slightly above the case will be another capacitor and circuit. All of these 'unintentional' circuits can have unforseen results. Granted at 50Mhz the results may be minimal, but those that play in the microwave region must pull their hair out, curse, and drink heavily. :)


Link to post
Share on other sites

your location haha cool, ok sorry I ment your contry and city :-)

I dont mind "hi-jacking" all are welcome here.

> All of these 'unintentional' circuits can have unforseen results

nope, you just have to play-along and use those extra circuits in your design, it will even improve performance by this.

in DC power filters for example, I always investigate the self resonant frequency of each component, and carefully select them to give me much better signal attenuation, see, coils will be self resonant as a parallel circuit with Q times the impedance, and caps will do the same as series resonanse = lower Z at the resonant point, perfect, just know this and test for it..

for RF coils where you need the inductance as clean value as possible,

you need to opperate them a good bit BELOW their resonance.

Link to post
Share on other sites

Hi Thomas,

glad u liked my little "trick or treat joke" for all those who havent gone to my "Location" ,its a tomb in the city of graveyards, Colma, California(ie one foot in the grave).

my area of operations is from Oakland California, to Monterey and points south.

I have several places I get to fly. All very dramatic, will post some video when finally airborne.



Link to post
Share on other sites

About 30 minutes ago the big brown truck brought me some coils from coilcraft and some caps from Mouser. I put them together as according to the schematic provided a few posts up. Using the frequency generator function of my antenna analyzer, I did a sweep from around 30Mhz up to 150Mhz. Monitioring the waveform on my cheap oscillosope, I noticed the amplitude decrease significantly above 60Mhz. When I connected the filter between my amp and my 6m mobile antenna I no longer wiped out the local 100.7 radio station, even when generating a 50.350Mhz feed signal and my radio only inches away. So, I am pretty sure it is working, but how do I know for sure? How do I tune it 'better'? On the antenna analyzer I get an SWR over 2.5 no matter what position I put the coils in. Here are some pics of a very rough hacked together part. I bought 6 of everything so that I could refine it after I had a working part. As always, thank you very much.



Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

  • Create New...