As a truly old EE who did not get real involved with the RF side of the world how would you check the resistance between the center conductor and shield of the coax after it was connected to the antenna? If there is no choke or balun of any type at the antenna end then it is probably possible. Any type of inductive device, especially those in higher wattage, current, devices would easily show conductivity I believe. With a new system I would want to know my cable/antenna SWR or SWRs at all the bands I would be using. Any issue with a choke would show up. I have a Rig Expert, Rig Stick that is super easy to use and would be glad to do a quick check or load for you to do that. I also have a NANO nva that is harder to use but work quite well. I practice Covid protocol so that complicates things a little but is manageable.
Chris Luppens - KG5BBF > On Feb 5, 2021, at 3:45 AM, Mark Brantana via BVARC <bvarc@bvarc.org> wrote: > > > 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 >> >> >> >> >> Virus-free. www.avast.com >> >> On Sun, Jan 31, 2021 at 7:33 PM Mark Brantana via BVARC <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 >>> http://mail.bvarc.org/mailman/listinfo/bvarc_bvarc.org >> >> >> -- >> Rick Hiller >> e-mail: rickhille...@gmail.com >> Cell: 832-474-3713 >> Physical: 9031 Troulon Drive >> Houston, TX 77036 >> >> Virus-free. www.avast.com > > ________________________________________________ > Brazos Valley Amateur Radio Club > > BVARC mailing list > BVARC@bvarc.org > http://mail.bvarc.org/mailman/listinfo/bvarc_bvarc.org > Publicly available archives are available here: > https://www.mail-archive.com/bvarc@bvarc.org/
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