Indoor 75m Antenna For An Apartment Dweller

[n3lrx]

I'm looking for indoor antenna solutions. I live in an apartment and cannot install anything outside. I've tried a mini-dipole (two 75m hamsticks) and I didn't have much luck with it. Not only was the antenna too big it made everything in the rack 'hot' I zapped myself just by touching the transmitter and that was only about 70w in tune mode. Using my tuner I can get the antenna down to a respectable ratio so that's not the problem.. Reception also sucked. I heard nothing anywhere on the 75m band. Not even slopbucket or CW.

Anyone have any ideas? 75m is the priority I'm not expecting miracles to get 160m working.. lol

The antenna would have to rated for 350w carrier and the legal limit PEP..

Any ideas greatly appreciated.

de Randy, N3LRX (YellRX)

[K1JJ]

Hi Randy.

Well, in general, on 75M expect to be down at least 15-20 dB from a standard full size outside dipole, no matter what you do inside.  A mobile whip on a car is usually down 12-15dB, so you may be as weak as a mobile or less.  You will do better as the frequency is increased.


How about setting up a killer car mobile installation and remotely control it from your shack?


Two suggestions for the apt:  Can you string a dipole on the ceiling, the length of the apartment inside?  Even if it's only 40' total length -   At the center use a large link coupled tuner with copper tubing and a vac variable.  


Another idea I've seen done:  Use very thin, "invisible" wire and throw one end up over the roof. Be sure the wire is lying on insulated shingles. Load this up as an end fed. No one will likely see it.

Downside: Your apt neighbors will likely experience RFI, especially at 1500 w pep. Being on AM they will quickly figure out what's going on.

I once lived in a 12 unit Denver apt running quad 4-400As and a 75M  inverted vee up on the roof. It was hidden well.    After two days I had a lynch mob at my door.  At the end of the month  I got an eviction notice for " Loud drilling noises at 3AM,  a dog (Yaz1)  and interfering with neighbor's TVs and stereos."


Hope you work out a good solution.

T

[AB2EZ]

A key issue is whether the building has a steel skeleton.  If it has a steel skeleton, it will act as a Faraday cage; and your indoor antenna will have very poor performance on 75m. On transmit, you will generate currents in the steel structure that will produce lots of RFI inside the building, possibly arcing across non conductive gaps, and very little coupling to external propagating modes.

Wiring (AC, telephone, cable, Ethernet), copper water pipes, and HVAC ducts will cause similar problems... depending upon their density, and how they are routed.

Stu

[n3lrx]

It could very well have a steel skeleton. The exterior is all brick and I know my walls are concrete I don't know if there is metal backing in the walls or not. I'm on the 3rd floor of a 7 story building so I'm not that high. But that makes throwing a wire up on the roof impossible and dropping a wire to the ground would only be about 20 feet..At this point I'd be happy if I could at least listen. But even the local AM broadcast stations are tough to get. I can only hear the 2 strongest stations and nothing else. I'll keep trying different options. Perhaps I may be able to put the mini-dipole on the west wall if I can get some way to hang it from the center. The west wall is also the longest wall in the apt. The antenna may just fit.

[WD5JKO]

Perhaps a short whip antenna, about 8' long could be poked out the window, or better yet off a balcony edge. Then work it against whatever grounds you can hook together.

When I was in college I did this with my Lear T30 ( 4 6L6's) HF aircraft transmitter. Running 20 watts AM with the window open a bit. This was in the winter when the outdoor temperature was often -15 degrees F. Between freezing out my room mate, and all them phono turntables, I seemed to be getting into every stereo in the dorm. Like with Tom, K1JJ, I had a lot of knocking on the door. 

Jim
WD5JKO

[w4bfs]

I dropped a 28 guage enameled wire from my dorm room 4th floor to a tree in the middle of a quadrangle while a student at TTU .... tuned it with a matchbox .... got out good but used up several spools of wire ... couldn't see it more than a few feet away unless the sun glinted off it

[n3lrx]

If I lived at the back of the building that would be an option. Unfortunately I'm in the front. It's all concrete and asphalt. No trees to hang from.
I may be able to set up a station at my mothers house. I haven't asked yet. But she has at least one tree I can work with. If all else fails I can try a vertical.

[WBear2GCR]

Who owns the building?
What is on the roof?

Can you post jpegs of the scene? Seeing it may reveal ideas...

Can you approach them?
Have $$ to offer?

The angle is "civil defense" in the event of an emergency.

Option 2: move.

[W3GMS]

I like the move one!  Either that or set up a Ham station at your Mom's.  If you run that much power you will likely be plagued with EMI / RFI issues not only in your own apartment, which you probably don't care about but with your neighbors. 

Sometimes you can find a rental place that is not in a complex.  Trade some rent for doing some maintenance and some Ham Radio antenna's.  Search the local papers for possible locations. 

I liked Tom's idea of a super mobile station if all else fails. 

Joe, GMS     

[wa3dsp]

I think 350 watts carrier  ( I am assuming near legal limit AM) and 1500 watts PEP are way to much power to run inside an apartment. It would definitely exceed the RF exposure limits and it would probably cause all kind of grief with yours and others electronic devices nearby but then Halloween is coming up so you could blame the flickering fluorescent lights on a spirit!

There are some nifty ways to remote rigs via the Internet and I would not leave that out as a possibility if you have another better location to put the RF. You could do just about everything you would do locally to control your station.

You are certainly not alone with this problem. Anything lower than 40 meters is very difficult in apartment dwellings mainly because of RFI on receive and transmit.

[n3lrx]

 Yeah, its a legal limit rig. It's a K7DYY Super Senior (k7dyy.com). I'm not as much concerned with RF exposure as I'm a certified nut case anyway.. Although I wouldn't want to give my iguana cancer.

 I'll have to check into lower power options to see if that's possible. I don't know of turning down the carrier on the transmitter also turns down the pwm output as well. It wouldn't be good feeding a transmitter that's dumping out 100/150 watts of carrier with 300 watts of audio.

But first the receiver issue. If I cant sort that out a transmitter is useless.

[n3lrx]

OK, I talked to Bruce, K7DYY and he said I can turn the carrier down and just adjust my input audio so I don't over modulate. That's easy enough. I was thinking I may need to do some internal adjustments to match the reduced carrier. With a bit less carrier I may be able to get this thing working. I was thinking of tuning it down to 200 watts or less. The only problem is still with the receiver. A transmitter is only as good as the receiver. If I can't receive any stations it's pretty pointless to have a transmitter. The option of setting up a station at my moms house is still an option even if I have to run a vertical it's better than nothing.

[W3NE]

I live in an apartment too, but at least I have a balcony previously used to support a Hamstick dipole on a strut extending about four feet from the railing. Maximum range was about 200 miles with 100W SB if the receiving end was in a quiet location. Ironically, best Tx direction was through the building! Now getting ready to try a screwdriver antenna supported at 45 degrees from horizontal using the copious nearby steelwork as a ground plane, on advice from two experienced manufacturers.

I think your best bet was suggested by WA3DSP: Station at Mom's with internet link, but if she objects, then look into Joe's suggestion to find a nearby property where your remote station could be located.

If you want to try receive-only, consider a shielded magnetic loop. In any case, high power inside your apartment is a non-starter. As a last resort, move to a twenty acre farm on top of a high hill.

Bob - NE

[Opcom]

I know of an installation where the cable TV shield, some 200 Ft long run, was used for a clandestine antenna. Not that I would recommend that or do it.

[flintstone mop]

OK, I talked to Bruce, K7DYY and he said I can turn the carrier down and just adjust my input audio so I don't over modulate. That's easy enough. I was thinking I may need to do some internal adjustments to match the reduced carrier. With a bit less carrier I may be able to get this thing working. I was thinking of tuning it down to 200 watts or less. The only problem is still with the receiver. A transmitter is only as good as the receiver. If I can't receive any stations it's pretty pointless to have a transmitter. The option of setting up a station at my moms house is still an option even if I have to run a vertical it's better than nothing.

Owning the K7DDY Sr. would make me move out of that apartment immediately!!! At your mum's place you would have a nice station and some good food to eat when you visit and operate.

[WBear2GCR]

Really more information would be nice.

It's kinda painful to read this actually. Running that sort of power on an inside antenna inside any modern building is really futile. The building will absorb so much RF going out or in.

You could work DX on 10m with the equivalent of a mobile whip connected to a window sill, outside.

                        _-_-

[kb3ouk]

Really more information would be nice.

It's kinda painful to read this actually. Running that sort of power on an inside antenna inside any modern building is really futile. The building will absorb so much RF going out or in.

You could work DX on 10m with the equivalent of a mobile whip connected to a window sill, outside.

                        _-_-

Too bad there wasn't a way to use all that metal to his advantage, like use the building as an antenna. I wonder how well it would work if you did neutral loading with the building's wiring, put the RF on the neutral side of the AC line similar to the way you do carrier current on the broadcast band (except that typically puts the load on the hot side). Problem is that might've worked years ago but in today's world of crappy electronics, probably would be way too noisy on receive and you'll get into everything on transmit.

[n3lrx]

Sorry, I don't know much about the building itself other than it was built by W.K. Kellogg in the mid 20's. When Kellogg built something he  built it to stand the test of time. Kellogg was also a bit crazy. There are stories about his borderline insanity floating around. One of those stories as that apparently part of his sanitarium burnt down and when he rebuilt he purposely built a bonfire in the basement just to prove his new building would not burn down. I'd assume he built this building in the same fashion.

I do know that my walls are concrete (makes hanging things almost impossible) so there very well could be steel mesh in the walls as well. This building was built as a private hotel (apparently Battle Creek's Waldorf Astoria at one time from what I hear) for people getting treatment at his sanitarium across the street. (Which is now the Battle Creek Federal Center.) I've also heard that it spent some time as a hotel after Kellogg as well. It was updated and converted into apartments in the 70s and has been apartments ever since. That is all I have heard about this building.

I can't put anything on the outside of the building or hang any antennas out the windows. Management rules. So I'm stuck with trying to get indoor antennas to work. Which as you stated is often futile. I'm beginning to see that now.

I'm not really interested in DX, to me across the street or a thousand miles away holds the same charm. I just love radio! The problem is I hear nothing. I can't even get broadcast AM in this apartment except for the 2 very local AM stations. There is no noise on the AM b-cast band, it's just dead. (Perhaps desense) The same for the ham bands. Not overly noisy just dead. I get about an S4-5 noise floor and nothing on top. No slop bucket, no CW. Listening on 3875 LSB at one point I was able to zero in on a very weak carrier of some sort but making out the voice was impossible.

UHF/VHF seems to have no problem (large windows I'm sure are the reason) although UHF/UHF RFI is high in the building. I get a lot of noise on my scanner on several frequencies that has made listening to them impossible without the use of CTCS (PL). That may be caused by my own computers as well. So I'm not entirely exempt from the cause some of my grief. I know my router puts out a wall of RFI and I'm not the only person in the building to have these noise makers.

Well, that's all that I know about this buildings history and construction. Not much of a help I know.

Perhaps this transmitter project could lead to insensitive to move out of this apartment and get a house where I can string antennas. Who knows.

[KB2WIG]

R,

To answer one of yer problems.......


http://www.homedepot.com/p/Ramset-Hammer-Shot-0-22-Caliber-Single-Shot-Tool-00022/100091715



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