EPT3600 high swr on SSB (spurious emission around 20 MHz)
-
- Regular
- Posts: 6
- Joined: 11 Sep 2018, 13:14
- Call Sign: 1MC
EPT3600 high swr on SSB (spurious emission around 20 MHz)
Hi folks,
I have a Pearce Simpson Super Cheetah (the black one 240 ch with EPT3600 fitted). In AM&FM all works fine. In SSB i have high swr connected to my antenna.
Investigating about that, i noted that on dummy load i don’t have any SWR at all in all modes.
Then suspecting an out-of-band emission i fire up my ic7300 and i found a very large (40-50 khz) spurious emission that goes up when i key in SSB, and floating up and down in frequency. Is very unstable. If i put my finger on metal screen of the vco coils, the emission disappear.
Other than leave my finger tapped on the coil, any suggestion ?
Cristiano 1MC - JN61sp
I have a Pearce Simpson Super Cheetah (the black one 240 ch with EPT3600 fitted). In AM&FM all works fine. In SSB i have high swr connected to my antenna.
Investigating about that, i noted that on dummy load i don’t have any SWR at all in all modes.
Then suspecting an out-of-band emission i fire up my ic7300 and i found a very large (40-50 khz) spurious emission that goes up when i key in SSB, and floating up and down in frequency. Is very unstable. If i put my finger on metal screen of the vco coils, the emission disappear.
Other than leave my finger tapped on the coil, any suggestion ?
Cristiano 1MC - JN61sp
-
- Radio Addict
- Posts: 509
- Joined: 04 Oct 2015, 08:10
- Location: Sydney, Australia
Re: EPT3600 high swr on SSB (spurious emission around 20 MHz)
Most likely the RF output stage is oscillating. A quick way to tell is to measure the SWR on AM at channels 1 and 40, there should be a difference, even if it's only slight. On SSB, if it's a lot higher but doesn't change at all between 1 and 40 the RF output stage is oscillating, often from just after the transmit mixer. The SWR doesn't change on SSB because the channel selector and PLL are no longer controlling the frequency the radio is transmitting at.
An external frequency counter will show the carrier is a meg or two either above or below where it should be, i.e. in the 25 or 29 MHz region.
It can be caused by a bad patch cord, bad SWR meter internal earthing (M** meters are known for this where the mounting rivets they use fail to make good contact), loose PCB screws inside the radio, a failed solder joint on the radio board, or a bad / damaged (ceramic bypass) capacitor. Try joining (a short screwdriver works well as a test) a metal tuning can near the mixer stage to the metal case of the radio, seen more than one radio that someone has "cured" this way.
Some radios have such poor shielding that operating them with the top cover off will cause the oscillation to occur...
An external frequency counter will show the carrier is a meg or two either above or below where it should be, i.e. in the 25 or 29 MHz region.
It can be caused by a bad patch cord, bad SWR meter internal earthing (M** meters are known for this where the mounting rivets they use fail to make good contact), loose PCB screws inside the radio, a failed solder joint on the radio board, or a bad / damaged (ceramic bypass) capacitor. Try joining (a short screwdriver works well as a test) a metal tuning can near the mixer stage to the metal case of the radio, seen more than one radio that someone has "cured" this way.
Some radios have such poor shielding that operating them with the top cover off will cause the oscillation to occur...
-
- Regular
- Posts: 6
- Joined: 11 Sep 2018, 13:14
- Call Sign: 1MC
Re: EPT3600 high swr on SSB (spurious emission around 20 MHz)
Thank you for your detailed reply.lbcomms wrote: ↑17 Apr 2020, 17:41
It can be caused by a bad patch cord, bad SWR meter internal earthing (M** meters are known for this where the mounting rivets they use fail to make good contact), loose PCB screws inside the radio, a failed solder joint on the radio board, or a bad / damaged (ceramic bypass) capacitor. Try joining (a short screwdriver works well as a test) a metal tuning can near the mixer stage to the metal case of the radio, seen more than one radio that someone has "cured" this way.
Some radios have such poor shielding that operating them with the top cover off will cause the oscillation to occur...
SWR meter is a Daiwa CN-901 HP3. And yes, i'm aware to stay far away from those M** Made For Junk meters... i'll try to identify and cure the autooscillation in some manner. The strange thing is the RF emission around 20 MHz IIRC that in AM and FM i don't have at all. AM/FM are steady and without "out of band" carriers ( i don't have a spectrum analyzer but i adapt my RSP1A with 10 MHz of bandwidth with proper attenuation and my IC-7300 as general coverage RX).
Tomorrow i try to post you some video or photo of the problem.
TY and 73,
Cristiano
-
- Radio Addict
- Posts: 509
- Joined: 04 Oct 2015, 08:10
- Location: Sydney, Australia
Re: EPT3600 high swr on SSB (spurious emission around 20 MHz)
When you transmit on AM or FM there is a carrier that will swamp the oscillation in most cases, so you'll only see the fault on SSB.
Also, many bipolar (i.e. not MOSFET) final radios disable the driver / final bias voltages when not on SSB (not needed for AM or FM), and the stage won't oscillate unbiased.
Use a frequency counter to measure the frequency of oscillation if you have one, something like a receiver designed for looking at millivolt / microvolt level signals will be easily overloaded by the power level of an adjacent transmitter. Watch the frequency as you touch the metal cans (usually around the Tx mixer or predriver area) with your finger, you'll see a slight change when you touch the culprit. When you find it, short its can to the metal case of the radio and see if the oscillation stops.
Never seen a Daiwa meter cause this, but try another patch cord if you have one. Also, check the mounting screws or nut on the radios antenna socket, a loose ground there can cause this too.
Also, many bipolar (i.e. not MOSFET) final radios disable the driver / final bias voltages when not on SSB (not needed for AM or FM), and the stage won't oscillate unbiased.
Use a frequency counter to measure the frequency of oscillation if you have one, something like a receiver designed for looking at millivolt / microvolt level signals will be easily overloaded by the power level of an adjacent transmitter. Watch the frequency as you touch the metal cans (usually around the Tx mixer or predriver area) with your finger, you'll see a slight change when you touch the culprit. When you find it, short its can to the metal case of the radio and see if the oscillation stops.
Never seen a Daiwa meter cause this, but try another patch cord if you have one. Also, check the mounting screws or nut on the radios antenna socket, a loose ground there can cause this too.
- cb4ever104
- Legend
- Posts: 6561
- Joined: 28 Jul 2011, 21:26
- Location: España
Re: EPT3600 high swr on SSB (spurious emission around 20 MHz)
I've only seen (and had) this issue with the later Malaysian EPT3600 made boards . Never had it with any of the Taiwan ones . Not sure why that is . Sue has already covered all the possible culprits . Pcb screws and capacitor issues are the main culprits I've seen . I know that Nick (Black Spirt) sometimes tends to swap out the final and driver for Mosfets which also cures it . Not sure why exactly this is .
Sammy
Sammy
30TM060
Paul aka "Sammy". (108) PY60 Old Paisley DX Group (RIP Rab Markie)
Ex GM0 , now EA5 .
Handle "Fortune Hunter" back in "the day"
Radios ....? Anything that says "TAIWAN R.O.C" on the back.
Paul aka "Sammy". (108) PY60 Old Paisley DX Group (RIP Rab Markie)
Ex GM0 , now EA5 .
Handle "Fortune Hunter" back in "the day"
Radios ....? Anything that says "TAIWAN R.O.C" on the back.
- 14CS06
- Top Poster
- Posts: 1796
- Joined: 04 Mar 2012, 09:15
- Location: JN33LN - ALPES-MARITIMES-06 France
Re: EPT3600 high swr on SSB (spurious emission around 20 MHz)
Photo Collector CB RADIO
- ch25
- Top Poster
- Posts: 1675
- Joined: 03 Dec 2016, 11:07
- Call Sign: Lemmy
- Location: Poland
Re: EPT3600 high swr on SSB (spurious emission around 20 MHz)
Take 47n and 68R and place like on image.
Chris
That should prevent driver/final from oscillating.Chris
You do not have the required permissions to view the files attached to this post.
WE ARE MOTÖRHEAD, AND WE PLAY ROCK N' ROLL
You can't have too many antennas...
You can't have too many antennas...
- cb4ever104
- Legend
- Posts: 6561
- Joined: 28 Jul 2011, 21:26
- Location: España
Re: EPT3600 high swr on SSB (spurious emission around 20 MHz)
Hi Chris . The image you posted is called B300P . I presume you've uploaded the right one ? I just want to confirm that the mod you're suggesting should be done on both the Driver (2166) and Final (1969/2312) of the Ranger pcbs ? Like on the 3900 for example ?
Sammy
You do not have the required permissions to view the files attached to this post.
30TM060
Paul aka "Sammy". (108) PY60 Old Paisley DX Group (RIP Rab Markie)
Ex GM0 , now EA5 .
Handle "Fortune Hunter" back in "the day"
Radios ....? Anything that says "TAIWAN R.O.C" on the back.
Paul aka "Sammy". (108) PY60 Old Paisley DX Group (RIP Rab Markie)
Ex GM0 , now EA5 .
Handle "Fortune Hunter" back in "the day"
Radios ....? Anything that says "TAIWAN R.O.C" on the back.
- ch25
- Top Poster
- Posts: 1675
- Joined: 03 Dec 2016, 11:07
- Call Sign: Lemmy
- Location: Poland
Re: EPT3600 high swr on SSB (spurious emission around 20 MHz)
Yes, like you marked red.
47nF ceramic type.
Chris
47nF ceramic type.
Chris
WE ARE MOTÖRHEAD, AND WE PLAY ROCK N' ROLL
You can't have too many antennas...
You can't have too many antennas...
- cb4ever104
- Legend
- Posts: 6561
- Joined: 28 Jul 2011, 21:26
- Location: España
Re: EPT3600 high swr on SSB (spurious emission around 20 MHz)
OK . Thanks . I'll try that the next time I get that issue .
30TM060
Paul aka "Sammy". (108) PY60 Old Paisley DX Group (RIP Rab Markie)
Ex GM0 , now EA5 .
Handle "Fortune Hunter" back in "the day"
Radios ....? Anything that says "TAIWAN R.O.C" on the back.
Paul aka "Sammy". (108) PY60 Old Paisley DX Group (RIP Rab Markie)
Ex GM0 , now EA5 .
Handle "Fortune Hunter" back in "the day"
Radios ....? Anything that says "TAIWAN R.O.C" on the back.
-
- Regular
- Posts: 6
- Joined: 11 Sep 2018, 13:14
- Call Sign: 1MC
Re: EPT3600 high swr on SSB (spurious emission around 20 MHz)
Thank you guys.
Spent 3 hours this afternoon to fix a NOS Grant with no audio in RX, a 47mF condenser drives me crazy, now is sounding brand new.
Is a Grant with 40/45 meter transverter fitted in origin by the italian official importer, mr. Marcucci.
Tomorrow i'll try the RC mod - thank you a lot. I have two of those super cheetah NOS with that problem, and if that fix the prblem - and i'm pretty sure that the mod will fix it - a virtual beer for all you guys helped me
73 and stay safe,
Cristiano 1MC
Spent 3 hours this afternoon to fix a NOS Grant with no audio in RX, a 47mF condenser drives me crazy, now is sounding brand new.
Is a Grant with 40/45 meter transverter fitted in origin by the italian official importer, mr. Marcucci.
Tomorrow i'll try the RC mod - thank you a lot. I have two of those super cheetah NOS with that problem, and if that fix the prblem - and i'm pretty sure that the mod will fix it - a virtual beer for all you guys helped me
73 and stay safe,
Cristiano 1MC
-
- Registered New User
- Posts: 1
- Joined: 14 Sep 2020, 19:22
Re: EPT3600 high swr on SSB (spurious emission around 20 MHz)
Hi, I have a SS3900 with oscilation problems, i´ll try this fix.
thank you
thank you
- cb4ever104
- Legend
- Posts: 6561
- Joined: 28 Jul 2011, 21:26
- Location: España
Re: EPT3600 high swr on SSB (spurious emission around 20 MHz)
It worked for me the last time I had it.
30TM060
Paul aka "Sammy". (108) PY60 Old Paisley DX Group (RIP Rab Markie)
Ex GM0 , now EA5 .
Handle "Fortune Hunter" back in "the day"
Radios ....? Anything that says "TAIWAN R.O.C" on the back.
Paul aka "Sammy". (108) PY60 Old Paisley DX Group (RIP Rab Markie)
Ex GM0 , now EA5 .
Handle "Fortune Hunter" back in "the day"
Radios ....? Anything that says "TAIWAN R.O.C" on the back.