Rick, Something weird is going on. I did a continuity test between the inside and outside conductors of the coax, and found a short from the line as it leaves the shack. Now I have to get back on the roof and determine whether it is the coax or the antenna. I sniffed around with an oscilloscope probe for RF, and found things surprisingly clean. So, I have a problem after the coax connection. Probably the static is a result of not having any active antenna to speak of. More to come in this saga, I am sure. The strange part is that this is a brand new coax, and a brand new MFJ-2010 OFDP. My money is on the antenna matcher. I am sure that will not be the only issue. Glad I decided not to key the radio!
Mark See below: > On Jan 31, 2021, at 8:45 PM, Rick Hiller <rickhille...@gmail.com> wrote: > > Mark, A few questions, comments and tests: > Sounds like a radio problem to me...so....not in any particular order, just > what I thought of first to last.... > . > -- What S level is the noise? Varies between about 1 & 9 Does it change > level with the RF Gain control? RF Gain is at max. Backing it off makes it > quieter, but reduces the signal as well. > -- What if you disconnect your antenna coax? Does it go away? The radio > becomes very quiet. > -- What if you connect a dummy load? Same noise? I need to get a dummy load. > -- What does the Nano VNA show? Impedance wise (R and j) and SWR? What is > the SWR bandwidth of the antenna across 40 and 20? > -- Where is your RF Gain pot? Maxed? Try reducing the setting a bit. > -- Do you have your "pre-amp" on? If so, turn it off. Preamp is off. NB > off too. Not sure what they call a noise blanker on this radio. > -- What about CW mode....does the Narrow filter on make a difference? > -- Where are the IF/PBT shift sliders set? They should be in the center for > a base reference. They are > > -- Are the rear panel Receive Antenna In and Out jacks jumpered and is the > jumper OK continuity wise? Pretty sure they are. Will have to confirm > > -- Is the Ham/General select switch in Ham position? I am not sure if the > band pass filters are bypassed in General....just a guess. Tried both. Same > > -- Take your coax off. Then using ONLY the center pin of the PL-259 insert > it into the radio SO-239 center ONLY. Is the noise similar? Then screw on > the PL-259 outside....does the noise change? Usually, using only the center > pin causes lots of receive noise and then when you screw on the 259 outside > the noise reduces as the antenna system is then a closed system. > You can also do this with a 10 foot long piece of wire and just connect the > wire to the inside center terminal of the SO-239 on the radio. The receive > noise should increase when you touch the wire to the center pin......is this > noise the same as you are complaining about? > > Have you run power to the antenna? What is the SWR? Similar to the Nano > reading? Use the internal SWR meter and meter switch to select RF PWR and > SWR set etc. > > That's about it for a 745 brain dump for tonight. Something is amiss in > your set up, IMHO, no external wideband white noise source is jacking with > ya. Sounds like receiver noise is at max gain and no received signals are > being processed. > > GL and 73...rick -- W5RH > > > > > > <https://www.avast.com/sig-email?utm_medium=email&utm_source=link&utm_campaign=sig-email&utm_content=webmail&utm_term=icon> > Virus-free. www.avast.com > <https://www.avast.com/sig-email?utm_medium=email&utm_source=link&utm_campaign=sig-email&utm_content=webmail&utm_term=link> > <x-msg://1/#m_5532074014698849640_DAB4FAD8-2DD7-40BB-A1B8-4E2AA1F9FDF2> > On Sun, Jan 31, 2021 at 7:33 PM Mark Brantana via BVARC <bvarc@bvarc.org > <mailto:bvarc@bvarc.org>> wrote: > I am reaching out for ideas on a radio issue. I have installed an IC-745 Icom > with an MFJ-2010 offset fed dipole. The power supply is a 20A MegaWatt > switching power supply, which is located right next to the radio. The antenna > is under some high power-lines with the long leg 90 degrees to the > power-lines. I used my nanoVNA to study the band SWR response, and everything > looks reasonable, though some small adjustments may need to be made. Nothing > is grounded as yet. > > Here’s my problem. I am only attempting to receive at this time and I get > consistent QRM white noise across all bands to the point where I can barely > pick out some voices, etc. > > I am confident that the antenna is properly connected due to my antenna study. > I don’t believe the power lines are an issue, since the problem would likely > be more isolated show up as birdies at certain frequencies. > The radio settings seem to all be correct according to the manual. > Lack of grounding, but again the white noise is generally consistant across > the spectrum. Still, this could be the problem. > I have turned off my computer, so there no QRM from its power supply. > It does not help to have the switching power supply right next to the radio, > but other users give good reports on this model and no QRM issues are > mentioned. > I tried the radio at different times of the day on 20-m voice band, with the > same noisy result. > It could be the net result of a large number of small device transformers, > but I doubt it. > I turned off the wifi, and still no change. > > Hmm… I am a little stumped. Any thoughts or ideas? Personal experiences? > > Mark > N5PRD > ________________________________________________ > Brazos Valley Amateur Radio Club > > BVARC mailing list > BVARC@bvarc.org <mailto:BVARC@bvarc.org> > http://mail.bvarc.org/mailman/listinfo/bvarc_bvarc.org > <http://mail.bvarc.org/mailman/listinfo/bvarc_bvarc.org> > > > -- > Rick Hiller > e-mail: rickhille...@gmail.com <mailto:rickhille...@gmail.com> > Cell: 832-474-3713 > Physical: 9031 Troulon Drive > Houston, TX 77036 > > > <https://www.avast.com/sig-email?utm_medium=email&utm_source=link&utm_campaign=sig-email&utm_content=webmail&utm_term=icon> > Virus-free. www.avast.com > <https://www.avast.com/sig-email?utm_medium=email&utm_source=link&utm_campaign=sig-email&utm_content=webmail&utm_term=link> > <x-msg://1/#DAB4FAD8-2DD7-40BB-A1B8-4E2AA1F9FDF2>
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