Linear RFI
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nn3v_6@...
Hi all.
I've seen the recent strings discussing the RM Italy HLA-305. I too have one, and it is a very nice linear to accompany the ELAD FDM-DUO. Truly a set and forget piece of equipment when operated in the AUTO mode. And a nice complement to a portable set-up. But I have one issue that eludes my effort to correct the problem. Any time I operate with the FDM-DUO at 4 watts output or greater, I get a huge amount of RFI in the shack.So much so that the modulation of outgoing digital signals is corrupted. I've tried anti-RFI measures. I've used toroid coils everywhere in the shack, including power cables and computer cables. NO RELIEF. I am pretty sure the matter is in the HLA-305, and when I use the FDM-DUO with my Alpha 89 linear, I actually achieve greater power out without a trace of RFI. Nothing. It is quiet as a mouse. By the way, I still am surprised that the alpha 89 works like a happy pupy with the FDM-DUO. But I'd like to solve the FDM-DUO / HLA-305 RFI problem, as that combination is an excellent portable set-up. Lugging an Alpha 89 around, together with the emergency generator for 220m volts is not a very realistic solution. Anyone have any ideas as a possible solution? 73 de NN3V |
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lasse moell
If you are using the same antenna and feeder and still only the HLA-305 give you RFI, I would look at the DC parts... maybe the RF sneaks out and affects the power supply or if you are using the same PS for both radio and PA you may try two separate supplies. Or maybe try a car battery to see if this improves the RFI situation. /Lasse SM5GLC 9 maj 2016 23:27:15 +02:00, skrev nn3v_6@... [elad_sdr_en] :
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Drew Riedle
I also have the same issue except mine is worse. Any time I use any type of amplifier with the DUO I get RF back into the transmit audio chain . it causes distortion on the transmit audio. This occurs when using an amplifier and exceeding 20 watts of output. I too have tried RF chokes on all cables using type 31 material. Have proper grounding and all the tricks I can think of. I have tried multiple antennas and amplifiers. I also get an ADC clip indication and fluctuating SWR indications on the DUO SWR indicator. None of this occurs with any of my other HR radios including my Flex 3000. Comments or suggestions appreciated.
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Thanks Drew
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ferrox4@...
Have you tried shortening the power cable from the power supply to the amp? Sent from my iPhone On May 9, 2016, at 5:27 PM, "nn3v_6@... [elad_sdr_en]" <elad_sdr_en@...> wrote:
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Charles Ristorcelli <nn3v_6@...>
Thanks Lasse.
I think I tried those a while ago, but I will do so again.
I do have toroids on the DC power lines. But I will also go back and verify that.
This has been a while, so I will retry everything.
73 & good DX!
Don't believe what you think! 73 de NN3V Charlie |
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jrichards@...
Any time I operate with the FDM-DUO at 4 watts output or greater, I get a
huge amount of RFI in the shack.So much so that the modulation of
outgoing digital signals is corrupted.
Anyone have any ideas as a possible solution? _____________________________________________ My solution ... I would sell it. Your mileage may vary, but I would not accept that sort of thing. Good luck resolving the issue - that would be no fun at all. Perhaps a simple solution will present itself soon. Just MY take... JHR --------------------------------------------------------------------------------- |
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Stig Rasmussen
RFI solving solutions will be different in each shack/installation. More information is needed. Are you a new ham? First rig/setup? You should explain mora about your setup, witch antenna, feeder, how far it is from shack, witch band, and at least.... Did this only happens with the Duo and not other rigs? Things like this.... Solving it is most done by earth connections, and ferrit on cables. Re-cabling. Experimenting. Lot of info at www.... But first CHECK antenna cables /connectors. #LB5VA_Stig_______73_ Fra: "jrichards@... [elad_sdr_en]" Til: elad_sdr_en@... Sendt: Tirsdag, 10. mai 2016 23.55 Emne: [elad_sdr_en] Re: Linear RFI Any time I operate with the FDM-DUO at 4 watts output or greater, I get a
huge amount of RFI in the shack.So much so that the modulation of
outgoing digital signals is corrupted.
Anyone have any ideas as a possible solution? _____________________________________________ My solution ... I would sell it. Your mileage may vary, but I would not accept that sort of thing. Good luck resolving the issue - that would be no fun at all. Perhaps a simple solution will present itself soon. Just MY take... JHR --------------------------------------------------------------------------------- |
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J Ferrow <ferrox4@...>
Shorten the cable from the power supply to the amp. Make it as short as possible within reason. I had an RM Italy kl-501 with some RF problems, as soon as I shortened the power cable all problems disappeared. If you dont want to cut up a "good" cable, Give it a shot with some junk cable and see what happens. On Tuesday, May 10, 2016 5:55 PM, "jrichards@... [elad_sdr_en]" wrote: Any time I operate with the FDM-DUO at 4 watts output or greater, I get a
huge amount of RFI in the shack.So much so that the modulation of
outgoing digital signals is corrupted.
Anyone have any ideas as a possible solution? _____________________________________________ My solution ... I would sell it. Your mileage may vary, but I would not accept that sort of thing. Good luck resolving the issue - that would be no fun at all. Perhaps a simple solution will present itself soon. Just MY take... JHR --------------------------------------------------------------------------------- |
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J Ferrow <ferrox4@...>
everyone is blaming the amp, maybe its the Duo?? On Tuesday, May 10, 2016 7:51 AM, "Drew Riedle drew.riedle@... [elad_sdr_en]" wrote: I also have the same issue except mine is worse. Any time I use any type of amplifier with the DUO I get RF back into the transmit audio chain . it causes distortion on the transmit audio. This occurs when using an amplifier and exceeding 20 watts of output. I too have tried RF chokes on all cables using type 31 material. Have proper grounding and all the tricks I can think of. I have tried multiple antennas and amplifiers. I also get an ADC clip indication and fluctuating SWR indications on the DUO SWR indicator. None of this occurs with any of my other HR radios including my Flex 3000. Comments or suggestions appreciated. Thanks Drew
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Steve Troyer
I do not have a problem with RFI. I do have massive grounding and make sure that the amp is also grounded even though the RM Italy 300 Plus I run does not have any grounding lug.
I have found that it is quite often a poor ground that causes these types of problems. That and harmonic resonance with some of the wire used to power the rig. I have two 8 foot copper ground rods outside the house and run flat copper wove ribbon to them. Flat copper wove ribbon does not make for a good transmitting antenna as does round copper wire and so any RF would be sent to the ground never to bother me. My grounding bar inside the shack is an aluminum flat 1/8 x 2 inch x 4 foot bar and has grounding points all along it. I've solved friends RFI problems by installing correct grounding for them. Quite often people ground to water pipes and that is not a good ground. Sometimes the plumbing in the house is interrupted by plastic or non metallic parts that prevent a good ground. I have seen grounding installed on plastic water pipe. |
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No problem here with Fdm-Duo driving the Hardrock-50 to 50w output. Use only the power cord for ground, and Johnson match-box to 4" spaced feeders to dipole.
Sent from my iPad |
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Charles Ristorcelli <nn3v_6@...>
Hi all.
Thanks for the comments. I will try a general answer to all the questions.
I think it is significant that several others have commented on similar problems when operating the DUO with a linear. May be more common than we realize.
As to more specifics on my set-up.
NOT a newbie. Extra class licensee since 1976. Operated innumerable ham shacks as I moved all over the world in my Navy career. Never had an RFI problem until this.
Important to note that I said my FDM-DUO operates my Alpha 89 with output of 200 watts WITHOUT any RFI.
Station set-up starting AT DUO: 1. DUO 2. HLA-305 3. Alpha 89 linear. 4. Power/SWR meter. 5. LMR-400n coax run to antenna. 6. 4 Element Steppir Yagi at 55 feet.
All power cables kept as short as possible. All extraneous wires (USB cords to computer, audio lines, etc.) wrapped around toroid coils. All equipment grounded to earth.
DUO/HLA-305A RFI experienced whether operated through the Alpha 89, or if Alpha 89 is taken out of the set-up entirely, and the DUO and HLA-305 are run directly to power meter and antenna.
With HLA-305 powered OFF, but running FDM-DUO through inert HLA-305A into Alpha 89, and then getting 200 watts out of Alpha 89, NO RFI.
Any comments or suggestions?
That is as concise as I can be in describing the set-up. Don't believe what you think! 73 de NN3V Charlie |
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lasse moell
Charlie, what type of RFI do you encounter? I guess this will be instrumental in trying to understand what is going on here. /Lasse SM5GLC 11 maj 2016 18:05:07 +02:00, skrev 'Charles Ristorcelli' nn3v_6@... [elad_sdr_en] :
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Very often RFI problems are generated by
connecting an unbalanced feed line
(e.g. a coax cable) to a balanced load (e.g. a dipole or an inverted V) without the use of a balun, which, as its name implies, transforms a balanced load into an unbalanced one. I found very effective the use of the current balun proposed years ago by W2DU, which takes the form of cylindrical toroids around the terminal part of the coax. As a picture is worth one thousand words, this is how I implemented it when erecting my antenna. Absolutely no RF in the shack, using a 300W linear amp.  73� Alberto� I2PHD |
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Neil Smith G4DBN
Hi Charlie, is the HLA running from a separate PSU from the DUO? I run some SSPAs running from separate 28v and 50V DC supplies with no problems, but I haven’t tried any 12V amplifiers on the same or separate supplies. I was thinking of getting an HLA, but in the end I decided to build a 28V amplifier based on Communications Concepts board and LPFs instead. I also use my Duo with a big old amplifier with a pair of 3-500ZGs to about 180W out with no ill effects.
Had you tried inserting a 3dB or 6dB pad between the DUO and the HLA to see if that reduces the problems faster than the drop in power? Not sure how well-behaved the input impedance of the HLAs is, could be it is nonlinear with voltage or something, and that is causing problems with the PA of the Elad. Putting an attenuator in line might indicate whether the problem is actually a parametric pumping effect or is caused by induced currents in the negative power lead or something. I would also try looking for RF currents in any of the power leads or the coax, using a split ferrite core wound with a few turns of enamelled magnet wire, and put that into a diode/capacitor/meter to indicate the current. Also you could try inserting low-series-resistance capacitors of 10nF or so in a break in the centre conductor and braid of the coax between the DUO and the linear so there is no DC path. A 1:1 isolating balun/unun would also work for that. Good luck with finding the root cause. Neil G4DBN |
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Charles Ristorcelli <nn3v_6@...>
Thanks for several comments.
If RF on power leads were the problem, I find it highly unlikely the problem is only present when the HLA is outputting only some 50 or 60 watts if the Alpha 89, located physically adjacent to the HLA, runs 1.5 KW with no RFI anywhere in the shack whatsoever.
I do not use unbalanced feedlines. The feedline from the shack to the SteppIr is LMR-400 coax, and the SteppIr indicates an SWR of “0”, or 1.0 for the absolute purist out there. And there are no differences in SWR under any of the set-ups I described, and none with my Yaesu FT-5000.
The HLA and the FDM-DUO are powered from separate power supplies.
The RFI manifests itself as a distortion in the transmitted waveform. In the digital mode, a local ham tells me that when I transmit with the FDM-DUO alone, or with the FDM-DUO powering the Alpha 89, the transmitted signal is clean, and the reception is 100%.
When the FDM-DUO transmits with the HLA-305A the received signal in digital mode is “warbly” (I’ve listened to a recorded sample at my friend’s QTH), and the digital print output on receive is negligible if copyable at all.
In the latter case, if transmitting SSB, the audio is distorted under the same transmit conditions, Distorted with the HLA but no distortion with the Alpha 89 or the DUO.
I will keep looking for causes and fixes. Thanks for all the comments. Keep them coming.
Don't believe what you think! 73 de NN3V Charlie |
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On 5/12/2016 3:36 PM, 'Charles
Ristorcelli' nn3v_6@... [elad_sdr_en] wrote:
Well, I don't know how the LMR-400 coax is
built, but, if it is like the other coax cables, it is
unbalanced.... I don't know if the Steppir has a balun
built-in, to convert from a balanced antenna to an unbalanced --
73 Alberto I2PHD Credo Ut Intelligam |
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Andreas Rehberg
Ok Charlie,
So we might concentrate on the things which are different between the two setups.. this is at least the power supply of the HLA.. incl. the DC and AC cables..
maybe you also use different coax cables from the DUO to the two amps..
73, Andy, DF4WC
(and well, coax is unbalanced, LMR-400 is coax, a SteppIR has a balun, and also with an SWR of 1:1 you can have a whole lot of RF on the shield)
Gesendet: Donnerstag, 12. Mai 2016 um 15:36 Uhr
Von: "'Charles Ristorcelli' nn3v_6@... [elad_sdr_en]" An: elad_sdr_en@... Betreff: [elad_sdr_en] Re: Linear RFI
Thanks for several comments.
If RF on power leads were the problem, I find it highly unlikely the problem is only present when the HLA is outputting only some 50 or 60 watts if the Alpha 89, located physically adjacent to the HLA, runs 1.5 KW with no RFI anywhere in the shack whatsoever.
I do not use unbalanced feedlines. The feedline from the shack to the SteppIr is LMR-400 coax, and the SteppIr indicates an SWR of “0”, or 1.0 for the absolute purist out there. And there are no differences in SWR under any of the set-ups I described, and none with my Yaesu FT-5000.
The HLA and the FDM-DUO are powered from separate power supplies.
The RFI manifests itself as a distortion in the transmitted waveform. In the digital mode, a local ham tells me that when I transmit with the FDM-DUO alone, or with the FDM-DUO powering the Alpha 89, the transmitted signal is clean, and the reception is 100%.
When the FDM-DUO transmits with the HLA-305A the received signal in digital mode is “warbly” (I’ve listened to a recorded sample at my friend’s QTH), and the digital print output on receive is negligible if copyable at all.
In the latter case, if transmitting SSB, the audio is distorted under the same transmit conditions, Distorted with the HLA but no distortion with the Alpha 89 or the DUO.
I will keep looking for causes and fixes. Thanks for all the comments. Keep them coming.
Don't believe what you think! 73 de NN3V Charlie
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Neil Smith G4DBN
Charlie, to remove the antennas/feeders from the equation, what happens if you run the HLA into a shielded dummy load? Can you monitor on another radio to see if the problem is still there without the antenna? That would let you isolate the problem down to a DUO/HLA interaction without any other influences.
Did you manage to test with an attenuator or a 1:1 ferrite transformer between the DUO and the HLA to remove the DC path down the coax outer? Neil G4DBN |
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Charles Ristorcelli <nn3v_6@...>
Thanks Alberto.
Shame on me!!
In the rush of writing my comments I inadvertently spoke poorly. What I really meant to say was that my lmr-400 coax is terminated in a 4:1 Balun.
The “magnitude” of SWR as 1 always leads to a semi-religious-technology argument for which I cannot find positive solution.
To say 0 SWR is somewhat an artificial statement. I usually infer that an SWR of 1 means a great match.
In either case, I have not found any possible explanation as to why the HLA-305 causes the RFI problem when the Alpha 89 located in the same place in the shack produces NO RFI even when running 1.5 KW.
To the question asked somewhere in this long string, the coaxial run from the rigs does not have multiple separate paths. The coaxial cable run OUT of the DUO is:
FDM-DUO to HLA-305A to Alpha 89 to SWR/POWER meter to antenna.
When I run the DUO + HLA-305, they transmit through the Alpha 89 which is not powered.
When I run the FDM DUO with the Alpha 89, the DUO transmits through the HLA-305 which is not powered, and into the Alpha 89 which is powered.
I’ve inserted the SWR/POWER meter once at a time between each component and measured 1.0 SWR when the total is terminated in the SteppIr antenna.
The FDM-DUO + HLA-305 alone give me some 180 – 200 watts depending on the band. The FDM-DUO is operated at 5 watts for this situation.
When the FDM-DUO is operated with the alpha 89, I run the FDM-DUO at 5 watts, and the alpha 89 provides about 300 watts.
When I really want to break a pileup, I run the FDM-DUO at 1.5 watts, getting about 30 watts from the HLA-305, and that run into the alpha 89 give me 1.5 KW out.
I thought I had experimented with the FD-DUO + HLA-305A transmitting into a 50 ohm dummy load once before, but I do not remember the result. I will do so as soon as I have a moment.
Thanks to all for the comments.
Don't believe what you think! 73 de NN3V Charlie |
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