Chris Thank you for your generous offer. However, Based on your comments and Rick’s, I guess I should expect a full dc conductivity reading; especially since the coax and antenna are commercially made. It is unlikely that there’s anything amiss with them. I did have to open the box to seal it since MFJ didn’t. (I then added a small weep hole at the bottom.
BTW The spectrum scan seemed reasonable, though the antenna may need tuning a little. The next possibility I need to check out is one that I do not like. The antenna is pointed towards a transformer. This is a fairly new transformer since the old one blew up a couple years ago. But it could possibly be because of all my QRM issues. Additionally, that same end of the antenna is reasonably low about 6 feet high. It does pass under some electric lines. Still theorizing. I probably need to try this radio at a different QTH. Thank you Mark N5PRD Sent from my iPhone > On Feb 5, 2021, at 9:43 AM, Chris Luppens via BVARC <[email protected]> wrote: > > 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 <[email protected]> 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 <[email protected]> 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 <[email protected]> >>>> 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 >>>> [email protected] >>>> http://mail.bvarc.org/mailman/listinfo/bvarc_bvarc.org >>> >>> >>> -- >>> Rick Hiller >>> e-mail: [email protected] >>> Cell: 832-474-3713 >>> Physical: 9031 Troulon Drive >>> Houston, TX 77036 >>> >>> Virus-free. www.avast.com >> >> ________________________________________________ >> Brazos Valley Amateur Radio Club >> >> BVARC mailing list >> [email protected] >> http://mail.bvarc.org/mailman/listinfo/bvarc_bvarc.org >> Publicly available archives are available here: >> https://www.mail-archive.com/[email protected]/ > ________________________________________________ > Brazos Valley Amateur Radio Club > > BVARC mailing list > [email protected] > http://mail.bvarc.org/mailman/listinfo/bvarc_bvarc.org > Publicly available archives are available here: > https://www.mail-archive.com/[email protected]/
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