eHam

eHam Forums => HomeBrew => Topic started by: KH2BR on November 10, 2017, 09:35:09 AM



Title: Is there a users group for kitsandparts.com?
Post by: KH2BR on November 10, 2017, 09:35:09 AM
Having some problems with the kits and parts.com 5 watt rf amplifier self oscillation and I am looking for the users group.
I remember there was one, but can't find it. Any one know where it is??

Robert KH2BR


Title: RE: Is there a users group for kitsandparts.com?
Post by: KG4RUL on November 10, 2017, 12:56:40 PM
Sounds like a chance for you to go to groups.io and start one?


Title: RE: Is there a users group for kitsandparts.com?
Post by: KH2BR on November 10, 2017, 03:15:14 PM
BUMMER !!  May be he still has his old forum hidden on the website. Will contact him when I find my round to it.


Title: RE: Is there a users group for kitsandparts.com?
Post by: VK4FFAB on November 11, 2017, 01:19:51 PM
BUMMER !!  May be he still has his old forum hidden on the website. Will contact him when I find my round to it.


Or you could post the issue here and let the brains trust offer you suggestions on the cause.


Title: RE: Is there a users group for kitsandparts.com?
Post by: N7EKU on November 11, 2017, 04:08:47 PM
Looks like you can still poke around in the old forum.  There is some info and advise about the amps in the RF Toolkits section.

http://kitsandparts.com/fluxbb/ (http://kitsandparts.com/fluxbb/)

73,


Mark


Title: RE: Is there a users group for kitsandparts.com?
Post by: N7EKU on November 11, 2017, 04:46:32 PM
Looks like you can still poke around in the old forum.  There is some info and advise about the amps in the RF Toolkits section.

http://kitsandparts.com/fluxbb/ (http://kitsandparts.com/fluxbb/)

73,


Mark

 Should be "advice" sorry.


Title: RE: Is there a users group for kitsandparts.com?
Post by: KH2BR on November 12, 2017, 07:56:47 AM
Thanks a lot Mark. When I give up, I will ask for help.

Robert
KH2BR


Title: RE: Is there a users group for kitsandparts.com?
Post by: AK0B on November 12, 2017, 05:41:36 PM
First I would check all wiring and the dressing of the wiring.  Expect your problem is workmanship or a part reversed, common mistakes when something does not fire up and work properly first time.

If eveything is ok then contact Kits and Parts I have always found him to be very responsive.

He uses excellent parts and instructions.

Stan AK0B



Title: RE: Is there a users group for kitsandparts.com?
Post by: KH2BR on November 13, 2017, 12:25:44 AM
I think I will re-wind the inductors. There may be some skinned enamel wires.
First problem was solved. I measured the impedance on the output of the amp with the antenna analyzer I mentioned above with power on and it came out to be 200 Ω so I rewound the output inductor and instead of 6 turns on the secondary, I used two turns and now it measured to 50 Ω .
Sure made a big difference in power output but now it is self oscillating even with the gain all the way down. This is the older amp. Pressing on, now to solve the self oscillation.

What am I building?? Its just a transmitter with an Arduino vfo. I don't want to hear the oscillator on frequency so I am using a NE602 mixer and a band pass filter. I had it on the air once and was checking reverse beacon and it did pick me up but oops !! it picked me up also 15khz above and below what I was transmitting on. Replaced the NE602 twice and was ok then. Guess it was bad but working sort of or just because it was made in china.. I am using a buck converter to power the arduino and cw keyer plus a pure sinewave side tone oscillator. Had to put a 1000mf filter cap on the output of the converter to knock down the converter ripple/hash from 95mv to 15mv. I could have used a LM device but dont like the heat they create.
Robert KH2BR



Title: RE: Is there a users group for kitsandparts.com?
Post by: N7EKU on November 13, 2017, 07:31:06 AM
Hi Robert,

I think I will re-wind the inductors. There may be some skinned enamel wires.
First problem was solved. I measured the impedance on the output of the amp with the antenna analyzer I mentioned above with power on and it came out to be 200 Ω so I rewound the output inductor and instead of 6 turns on the secondary, I used two turns and now it measured to 50 Ω .

It is not possible to check the impedance of an amplifier this way (and anyway, if you had any power coming out of the amplifier, you seriously risk frying your antenna analyzer).  The impedance of an RF power amplifier works the other way.  The load of the antenna (usually 50 ohms) is converted by the output amplifier, to the load required for the desired power output and for what the transistor can handle.  There is a formula for this for single ended and pushpull amplifiers.

Quote
Sure made a big difference in power output but now it is self oscillating even with the gain all the way down. This is the older amp. Pressing on, now to solve the self oscillation.

Changing from six turns, to two turns on the secondary (if you are meaning the side connected to the output) would reduce the power, not increase it.  If there was an increase in power out, it was most likely due to a soldering problem with the magnet wire, or some other winding problem.

For oscillations, I would also suspect soldering problems with the magnet wire.  This is the number one problem of homebrew equipment based on the number of problems I've seen with this.  Also double check the winding counts, check that the cores are the correct mix, and check component placement.

I've looked over the schematic and it seems well designed and should be stable.

Quote
What am I building?? Its just a transmitter with an Arduino vfo. I don't want to hear the oscillator on frequency so I am using a NE602 mixer and a band pass filter.

What are you mixing the VFO with?

Quote
I had it on the air once and was checking reverse beacon and it did pick me up but oops !! it picked me up also 15khz above and below what I was transmitting on. Replaced the NE602 twice and was ok then. Guess it was bad but working sort of or just because it was made in china.. I am using a buck converter to power the arduino and cw keyer plus a pure sinewave side tone oscillator. Had to put a 1000mf filter cap on the output of the converter to knock down the converter ripple/hash from 95mv to 15mv. I could have used a LM device but dont like the heat they create.

If you have another rig in the shack.  It would be much better to use that to check your signal.  Put the homebrew transmitter on a dummy load, transmit and check the signal width, as well as for harmonics of the fundamental.

You are using a low pass filter on the output?  This is a requirement for transistor amplifiers.

73,


Mark.


Title: RE: Is there a users group for kitsandparts.com?
Post by: KH2BR on November 13, 2017, 09:10:21 AM
Yes, a low pass filter is used.

Yes, another rig was used, I heard it but thought it was just due to over loading of the receiver so I didn't pay attention to it but only after discovering it on RBN. At that point, I started using another receiver to look for any other signals.

DDS output frequency at 2 mhz, mixing with a 5 mhz crystal resulting with 7mhz output feeding a 2n2222 amplifier connected to the band pass filter.

I don't have a spectrum analyzer. I disconnected power to the amp and started looking for other signals.
I thought I could have been over driving the mixer so I reduced the gain of the dds input but that did not work. Connected output of bandpass filter to another receiver, I just swapped out the mixer until that problem went away. The bad mixer showed a strange problem. I disconnected power to the mixer and it was still producing a 7 mhz output. Disconnected the dds and output went away. No dc voltage on the input of the mixer, I guess that the 2 mhz ac signal was enough to power it some way. Dont know, dont care, swapped it out and fixed it.

Now, for the Amp, I tried this antenna analyzer on a a couple other transmitters and it just simply works. I have also tried it on some receivers and it actually shows the 50 ohms impedance of each band. If the analyzer is not on the same band as the receiver, you can see way off.
 Have to make sure that the amp is powered on and not producing any spurious output. I dont want to fry my antenna analyzer.

I suspect the instability is in the driver circuit so I will re-do the transformers there and also the output transformer back to original configuration and try a a matching transformer on the output.
I tried a matching transformer on the input but that also caused instability with out a input signal.

I was a electronics tech in the military for 20 years but never involved rf electronics design.
now is a good time to learn.

Robert KH2BR


Title: RE: Is there a users group for kitsandparts.com?
Post by: N7EKU on November 13, 2017, 12:45:07 PM
Hi,

I suspect you are just seeing the impedance of the LPF for each band -- these filters are typically set for 50 ohms in and out.

If the amp were powered on, but the transistor is not turned on, then it presents to the primary winding an open circuit with some stray capacitance thus the final transformer would not affect the impedance such that it would depend on its winding ratio.  A tuned output network could be different, but this one is broadbanded.

I think you are on the right track with the oscillations.  Driver circuits can be more susceptible and depend a lot on how they are driven too.

73,


Mark.


Title: RE: Is there a users group for kitsandparts.com?
Post by: KH2BR on November 13, 2017, 01:36:43 PM
Its the driver. Touched the can which is the collector with a screwdriver, the spurious oscillation stops, its running at 45 mhz.
A while back when I put a inductive load on the input, it would go into oscillation, a resistive 50 ohm load, no oscillation.
I re-did the final output transformers but no effect. Almost there !!!! now, going to work on the driver transformers.

Robert KH2BR


Title: RE: Is there a users group for kitsandparts.com?
Post by: WD4HXG on November 13, 2017, 06:08:18 PM
Some possible fixes.

1 Make sure the driver is correctly dc biased.
2 Double check and make sure the degeneration circuit in the emitter has the right parts. Seriously, verify the correct values are there.
3 Place a ferrite bead on the base lead of the transistor. Usually a parasitic is higher in frequency but the bead might be enough to tame it.
4 Get a pair of pliers. Crush a bead into powder. Mix with urethane varnish or two part epoxy. Apply the mix of ferrite and varnish, or epoxy on the driver transistor case. Yeah I know voodoo and chicken bones but it has tamed more than one source of unwanted spurs for me.
5 Nip off the technican's finger previously applied and glue it to the driver case.  ;D

Regards

Chuck


Title: RE: Is there a users group for kitsandparts.com?
Post by: KH2BR on November 14, 2017, 06:51:48 AM
A reference note to the AM forum for me that has some information on taming parasitic's.

http://amfone.net/Amforum/index.php?topic=29211.0




Title: RE: Is there a users group for kitsandparts.com?
Post by: KH2BR on November 14, 2017, 05:03:46 PM
I did everything that I could find and finally broke down and replaced a supposably good driver and now it works just fine. My finger on the
case of the driver always stops the oscillation so the very last step was avoided and thats cutting off the tip of the finger
and glueing it to the case of the driver. :)

Robert KH2BR


Title: RE: Is there a users group for kitsandparts.com?
Post by: KH2BR on November 21, 2017, 08:18:56 PM
Well, Here is what I am up to. Driving a Penny Whistle amp to 25 watts plus LPF with this lash up.
Inside we have a arduino cw keyer, Mixer because I dont want to hear my vfo, mixer post amp, band pass filter, kits and parts driver amp. Spot function can switch on only mixer. Uses buck converter for 5 volts. !!  Found out that you need to filter the output of the buck converter because
it will result in a output signal at every 15khz. one display that does nothing but show my call sign. A dds pure sine wave generator for side tone.
Found a circuit to use for band switching BPF that will come next after I find arduino code to splice into the vfo software for switching. Just want to toggle 2 bits. Also need to learn how to properly
match sub assemblies to each other.
Robert KH2BR

(http://rholsti.tripod.com/aIMG_0245crop.jpg)

(http://rholsti.tripod.com/aIMG_0320.jpg)

(http://rholsti.tripod.com/aIMG_0323.jpg)