Ladder line running down PVC conduit through interior of home work?

[VA3AEX]

The XYL and I are buying a new townhouse. With no options to put an antenna outside between deed restrictions and the XYL’s rules of no visible wires I’m limited to an antenna in the attic. Attic is 20’x30’ and about 10’ tall at its peak. There will be no heating conduits, some electrical wiring to 2nd floor ceiling lamps running along the ‘floor’ of the attic. And roofing is asphalt shingles.

The builder has agreed to run a 2” PVC conduit from the attic to the basement (for free) to allow me to run a feedline. House is 2 stories above ground and conduit will be min of 2’ away from electrical wiring or HVAC ducts.

I  would like to get back on 75m/40m AM after a multi year absence, so this means a shortened antenna/good tuner/ladder line to hopefully get more power into the antenna. Any thoughts ladder line through PVC conduit will work? What shortened antenna design will work? Power is about 25w AM and at times 100w SSB. So no QRO and I recognize anything I put up will be a huge compromise and suited to local contacts.

73. Alex

[KY4SP]

I worked a fellow on 160 about a year ago that claimed to be running ladder line underground in PVC. He had as good a signal as anyone else on the band at the time.

Considering that trying it out is cheaper and less time consuming than finding a more accommodating XYL and/or a place without deed restrictions, what do you have to lose?   

[W1ITT]

Years ago there was a commercial open wire line with about one-inch spacing and clear plastic spreaders.  I haven't seen any in years.  If you like handcrafts, I suppose you could make some up on your own.  The faster solution would be to use the 450 ohm ribbon line.  Ideally use a balanced tuner at the rig instead of a balun on the output of an unbalanced tuner, and pay attention to a good RF ground at the rig.
You have roughly 35 feet to work with along the diagonal of the attic, and you'll want to bend the ends of the antenna along the short ends of the structure which would give you a bit more than a half wave on 40m.  You can model things on MMANA-GAL pretty easily.  My first iteration might be to go out 33 feet on each side from the center feed and insert perhaps a 10 mircohenry inductance there to make things happier on 80m.  I have a 66-foot center fed sloper for 40m and above (open wire line) off the tower and I have tried it on 80m.  It works OK on 80m as well, but not a barn burner.   A bit of folding back may be necessary, but don't overdo it.  Use good insulation at the ends as you'll have high RF voltages there and your neighbors will be upset if you burn the place down.  I hope you have stairs and don't have to worm your way up through a scuttle hole in the ceiling of a closet.
New construction will most likely have wired-in fire detectors and maybe intrusion alarms.  Be prepared to put mix-31 ferrite toroids multiwound on those leads if they are accessible topside.  Have the phone number for 911 handy so you can tell the fire department not to come in with the 4-inch hose open.
A few years ago in QST I had a short article about how, back in college days, I loaded up the red and green wires coming in on the Telco drop.  It wasn't strapping, but I was on the air.  For a camouflaged setup, I think you are one the right track with balanced feed.
73 de Norm W1ITT

[Detroit47]

I would think that a loop would be a better use of available space..
Johnathan N8QPC

[W1ITT]

A loop, aside from so-called "magnetic" loops, generally wants to be at least a wavelength in circumference.  His attic dimensions show only about 100 feet of circumference, which puts him somewhere around 10 mhz.  And that is low on the attic floor, nearer to all the wiring etc in the residence part of the house.  Shorter than a wavelength, the loop impedance goes low, making matching on 80 and 40m difficult.  A dipole can spend at least part of its run along the ridgepole, then down along an end rafter, getting it up higher...in the clear as much as is possible in this situation, and it'll have less coupling, both transmit and receive,  to all the stuff in the house.
For 20m or 15m a loop might be feasible, but to get down on the longer wavelengths with less critical matching, I still want the dipole.
73 de Norm W1ITT

[WO4K]

Watch out for those ceiling lights. No doubt they will be LED. When we remodeled out house and installed ceiling cans I had a horrible problem with RF from them. I had to put my coax (ham and TV) in flexible steel conduits. You may want to talk to your builder about using steel conduit instead of PVC for shielding.

[VA3AEX]

Thanks for the suggestions all! Never considered issue of LED lights as we will have them, so will look into the steel conduit idea. 73 Alex

[w9jsw]

At that power level I would think the DXEngineering 300 ohm window line would work fine. I used it on an outside dipole with a 1:1 current balun and and a tuner and had no issues with all but 160M at modest power levels. Inexpensive as well. 160M required the dipole to be over 200ft to get a match.

A better option may be to get a remote tuner and place that in the attic and feed it with coax.

[Detroit47]

How about something like the B&W folde dipole. I'm not saying  to buy one but the design is interesting.

https://www.bwantennas.com/bwds.html

N8QPC

[K3WKM]

I live in a restricted community so in my attic my antenna is 51′ center fed with 16′ of 450 ohm Wireman window line to a 1:1 choke balun and 16 inches of 9913 to the back of a Palstar auto tuner. It works better than I could expect for an attic antenna, Palstar has no problem tuning and using the ATU in the Flex 6500 also worked well. First contact was Italy from my QTH in Philadelphia followed by Cayman Island and Bermuda….all on 40 meters.
My shack is on the second floor...I used a 1.5" ID x 3" pvc coupler to go thru the ceiling.  To keep the window line centered in the coupler I packed it with fiberglass (remove any paper backing). I would bet for a longer run of PVC you could wrap the window line about every 6' with fiberglass and it would keep it centered in the tube. The choke balun is a Balun Design 1116du 5KW.....I'd recommend this site https://kv5r.com/ham-radio/ladder-line/ladder-line-page-2/#comment-11923    lots of good info, my antenna is described as a junior g5rv.   If ya need a pic or have a question email at k3wkm@arrl.net       

[VA3AEX]

Yikes on the prices of the B&W folded dipole! Has anyone DIY’d one which I assume is a terminated folded dipole?

K3WKM - I have DYI’d a Junior G5RV but never used it on 80/75M. With the tuner can you get it to ‘work’?

[W1ITT]

The B&W Folded Dipole is a version of the T2FD antenna.  It used to get some ink in the RSGB publications.  As I recall, the termination was a 400 ohm presumably noninductive resistor.  I once saw a NEC run on one of those and it showed that, below about 5 mhz, much of the transmit power was absorbed by the resistor.  The Brits like them because they have typically small yards, or "gardens" as they prefer, and they do manage to radiate some energy.  The military likes them because the SWR is fairly flat across a wide range, as is my dummy load, and they can just poke some more power to it.  A friend put one up for quick radio when he moved into a new place.  When he got around to putting up a plain dipole with open wire feed, he seemed to come up more than 10 db on 80m.
An attic antenna has a couple strikes against it already.  I'd still go with the dipole, open wire , and a balanced tuner.  It gives up less than any of the other trick antennas.

73 de Norm W1ITT

[K6JEK]

What about foliage? I want to run the 300 ohm window line along a fence line to a Matchbox to coax to the shack.  Would running it just on top of the ivy covering the fence cause grief? It sure would be easier than making a bunch of supports.

[K3WKM]

Take a look at this site.....lots of good window line info:
https://kv5r.com/ham-radio/ladder-line/