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EXCESSIVE COAX
- Thread starter Swamp Yankee
- Start date
I must admit that any time I hear someone say that coiling up coax forms an inductor, I assume they are talking about the inner conductor, mainly because they usually are talking about that. Lots of folks think that coiling it up will somehow reduce the power output because the cable forms an inductor. They back it up by saying that when they move the cable and straighten it out the SWR and power meters change which are classic signs of common mode currents but try explaining that to a lot of people.
So what to do with an extra 8' of stiff-ish 400?
I'm almost finished with a rig to radial antenna rebuild. I read the EXCESSIVE COAX thread above to conclude it depends on the antenna design and/or feed-point with regard to common mode current from not having an adequate ground system. That’s awfully complicated.
I should be fine without any coil by leaving it out for the OCF which is heavily choked (TRX Labs 4:1 Balun/Choke combo) but a simple 20m dipole w/ a 1:1 current Balun? ?
8' is only 3-4 turns 1' in diameter. I'm planning on placing it midway where the coax enters the building after a 35' vertical run to antenna. A big drip loop. I would like some heavily shielded cable for patch cords. My primary concern is TVI/Intercom/Stereo etc
Am I being reasonable by trying watch TV in the same room as kw HF transmitter? Idk,
neil, nyc
I'm almost finished with a rig to radial antenna rebuild. I read the EXCESSIVE COAX thread above to conclude it depends on the antenna design and/or feed-point with regard to common mode current from not having an adequate ground system. That’s awfully complicated.
I should be fine without any coil by leaving it out for the OCF which is heavily choked (TRX Labs 4:1 Balun/Choke combo) but a simple 20m dipole w/ a 1:1 current Balun? ?
8' is only 3-4 turns 1' in diameter. I'm planning on placing it midway where the coax enters the building after a 35' vertical run to antenna. A big drip loop. I would like some heavily shielded cable for patch cords. My primary concern is TVI/Intercom/Stereo etc
Am I being reasonable by trying watch TV in the same room as kw HF transmitter? Idk,
neil, nyc
You can do it, I run either browning rg8x doublsheild or lmr 240 for jumpers between equipment and also have a grounding bus that transceiver , amplifier and tuner are all connected to with flat copper braid going outside to a ground rod and I have no feedback issues in the house at all. Watch out for nasty noisy power supplies in your tv,s and monitors, some are better than others.
The 50' length of BR-400 (Browning name) had an intermittent short on one connector, so the excess length problem was addressed fixed with a new clamp-on connector.
Presently rebuilding the mast-mount coax Switch with Rec. Pre-amp and Balun. Pre-amp board worked very good so I ordered the model that has In/Out relays already on PCB (should have done that 1st time it seems). Same-same with my homebrew latching relay coax switch. I ordered a 2:1 coax switch PCB that need populating. Waiting for parts but I intend to upgrade the relays on pre-amp board. Not certain how the relays stay in position yet but doubt they are latching.
The re-configuration of my EFHW wire into an OCF also worked out well. SWR's across 10-40 are low enough (2-ish) for an ATU to handle with 11% ERP loss or less. OCF feed point at 25% using approx a total of 94' 12 awg stranded at 70' AGL. For short coax leads inside the mast-mount box I intend to use RG316. Doesn’t matter for Rec but Xmit idk yet. Maybe rg58 for the Pre-amp bypass lead (Xmit)? I have a max of 6 wires for VDC controls (1 pair 18awg solid with the other wires being lightweight 4 conductor telephone cord.
As odd as it may seem, the Internet is 'all over the place' on whether an OCF is Balanced or Unbalanced. I’m going with Balanced and made the 4:1 Balun / choke suggested by TRX Labs on YouTube.
Presently rebuilding the mast-mount coax Switch with Rec. Pre-amp and Balun. Pre-amp board worked very good so I ordered the model that has In/Out relays already on PCB (should have done that 1st time it seems). Same-same with my homebrew latching relay coax switch. I ordered a 2:1 coax switch PCB that need populating. Waiting for parts but I intend to upgrade the relays on pre-amp board. Not certain how the relays stay in position yet but doubt they are latching.
The re-configuration of my EFHW wire into an OCF also worked out well. SWR's across 10-40 are low enough (2-ish) for an ATU to handle with 11% ERP loss or less. OCF feed point at 25% using approx a total of 94' 12 awg stranded at 70' AGL. For short coax leads inside the mast-mount box I intend to use RG316. Doesn’t matter for Rec but Xmit idk yet. Maybe rg58 for the Pre-amp bypass lead (Xmit)? I have a max of 6 wires for VDC controls (1 pair 18awg solid with the other wires being lightweight 4 conductor telephone cord.
As odd as it may seem, the Internet is 'all over the place' on whether an OCF is Balanced or Unbalanced. I’m going with Balanced and made the 4:1 Balun / choke suggested by TRX Labs on YouTube.
Closing this thread out. Today I was able to try the new 10-40m OCF antenna, barefoot 65-80w max. Several contacts with POTA stations everywhere from Nova Scotia (20m) to Corpus Crispi coast (10m). I can hear everything!
Dentron ATU and OCF go together well. I can tune 10-40 (avoiding 15) nearly 1:1.1 throughout. I'll use OCF until I re-build mast-mount switch box (likely November as parts shipped from PRC). Looks like my old EFHW was defective.
Dentron ATU and OCF go together well. I can tune 10-40 (avoiding 15) nearly 1:1.1 throughout. I'll use OCF until I re-build mast-mount switch box (likely November as parts shipped from PRC). Looks like my old EFHW was defective.
England to G5MCL this morning 80w (28.395), this OCF antenna is working fine. All the work on Rec pre-amp was not really needed. It seems that my old antenna simply sucked. Sometimes lessons learned the hard way are best.
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