Good indoor HF antenna for Oxford-style room

[usukICOMuser]

I am trying to set up an HF antenna for my IC-R75 (with internal pre-amp) setup at Princeton University's Old Graduate College, which, for reference, looks like this: (http://ysfine.com/princeton/gcollege22.jpg). I am not allowed to use an external HF antenna, nor unfortunately am I allowed to attach an antenna to the large tower you see in the photo (that would have been amazing...). I also don't have a large budget, so I think a Wellbrook is out of the question for the moment.

For comparison, I also have an ICF-SW100 connected to an AN-LP1 (the AN-LP1 really doesn't work with an IC-R75...I tried it some time ago). It works decently enough; I'm able to listen in to ABC's overseas broadcast early mornings (5.30-6.00am), but the receiver's limitations mean that I can't listen to weaker stations or amateur.

What antenna might work? I live on the ground floor, with three windows surrounded by an old-fashioned metal enclosure. The walls are stone and cement, and RFI is present owing to computers, bad wiring, etc. I've tried just stringing up a '30 longwire along the inside window section of the room, but I mostly receive RFI and noise.

I've read vastly varying opinions on proximate antennas, e.g., the Ameco TPA., which leads me to believe that they're 'just adequate' at best. Universal Radio suggested the RF Systems EMF. But, once again, the short length of the wire, its inflated price, and widely differing reviews make me view the EMF with suspicion. Help!

 

[ka3jjz]

Your first problem is the RFI. You're going to need to clean that up as much as you can. Do a little detective work and see what the worst offenders are, and handle them first. Culprits include DSL modems (I have one and it's a royal pain in the arse...) and any loose wiring from the PC to a peripheral - which could act as an unintended radiator. Printers can be a source of noise, too. Turning everything off that you can and using your SW100 as a crude noise detector (tune to an unused HF or MW freq with the whip fully collapsed), turn each item on one at a time and see where the noise increases.

Next we need to consider the antenna itself. It would be better if you can physically separate the antenna in another room, away from the PC and other stuff. Probably the best way to go is a loop - a much bigger one than the AN-LP1. On an outside wall, wind a loop using thin speaker wire (clear wire makes it almost invisible) around the perimeter of the wall a few times, tie that off to a 9:1 transformer (some call it a magnetic longwire balun) and feed to the R75 with coax. This is, by the way, one of the solutions I'm considering for my situation which is not very dissimilar to yours....there are many plans on the Net, and a few, like Palomar and WinRadio, that sell their own brands (not very expensive).

HTH...Mike

 

[w2xq]

A general rule of thumb is the antenna should be a minimum of 5 meters away from the near-field electrical environment of a building. Given the materials and construction of most of the buildings on the Princeton University campus and you are living on a ground floor, I would probably go in a different direction. If you want to do something other than stream audio from the Web, putting a remote SDR at a quieter location (parents? relative? friend?) and controlling it through the Internet might be an alternative. But then if you are going to school, there's probably no budget. (A few centuries ago I used to work summers at the PU Store on campus.) In stock trading, there is an expression "don't fight the trend." Unfortunately I think that's applicable to you (and maybe Mike).

 

[woebbers]

Im gonna put my oar in the water here... I live in an Apartment surrounded by folks who have all types of RFI emmiting devices. What I did was buy a loop I bought the Pixel Pro-1A. I use a Winradio and a Icom R-75 along with a bunch of other project radios. The loop is roughly 1 meter in circumference,on a 2 foof piece of plastic pipe it sits about 5 foot high. Aimed towards the window the antenna does a better then average job on picking up DX. and the nulls are to my noisey neighbors..my noise level is aroound S5 and during certain times lower...so what im saying is it can be done..but the antenna is not cheap..I rarely use my preamps

Sal

 

[k9rzz]

Might I suggest, for whatever antenna that you decide to use, to think about a noise canceler and hook that up to a piece of wire (for the sensing antenna) in the room. At least, if you park on station to listen to, you'll be able to null out any local RFI and get a clear signal on your target.

Also, look into the Princeton Ham Radio Club. I tried some Google, but not coming up with much. At least you'll hook up with others interested in radio and maybe come up with a group solution!

Looks like an exciting challenge!

 

[ridgescan]

do Mike's suggestion but try the metal window enclosure as the antenna hey ya never know..

 

[nanZor]

Ouch! Like Mike mentioned, get the rfi under control first, and try to optimize for best signal-to-noise, rather than overall strength. I'm in a similar situation.

I'd use the S100 in ssb mode to hunt for a quiet area in the room if it can be found. Using nothing but the built in whip, carefully move the radio around perhaps INCHES at a time to see if you can get into a null somewhere. The good thing is that you are running from batteries, so that cuts out the variable of noise coming in from AC. And yes, don't discount going vertical with the whip as you move around. Of course the best place would be somewhere near the window if you are lucky. Try it on several of the bands you are interested in.

IF you do find a quiet little hole in the noise, try just a short wire with the R75 in that hole. And if it looks like you may be getting somewhere, consider running the R75 solely from a battery - say a 20 to 35 amp lead-acid sealed AGM deep cycle. You can recharge it with something like a "battery tender" charger (my fav for charging). Of course you can go smaller, but remember that deep-cycle SLA's don't like being drained past 50% capacity, so do the math for the R75's 900ma draw per hour of use to help you decide.

If you have found a real quiet hole, it is possible that you can run the R75's preamp(s) without them being just a noise amplifier, ruining the s/n. If that works, you might consider a very small antenna with a built-in tuner, such as the Miracle-Ducker TL. In this situation, a short antenna that doesn't cross into external noise fields will be of more benefit than a longer wire.

A lot of compromizes here to be sure, but finding that quiet hole with a short antenna is paramount. Let the S100 in ssb mode guide you...

 

[usukICOMuser]

Thanks everyone,

I tried the ICF-SW100 "searching" method last night. The lights (rather unbelievably) did not create much RFI, but the computer adapter created a tremendous amount. So first thing I'll do is to unplug the computer whenever I want to DX and simply run the laptop off the internal battery.

As for finding the quiet "hole," I did find one as well last night - the window area. So I repositioned the equipment there to test. The metal window frame seemed to hurt more than help, although it was a good idea in theory. A noise canceler (e.g., from Timewave or MFJ) might do the trick.

Regarding loops, from woebbers' comment I have a feeling that I will eventually have to purchase a proper loop (likely a Wellbrook). Too, it's small enough that I may be able to negotiate with facilities to permit its outside installation (perhaps if I obtain a 2nd- or 3rd-story room in the fall). I'll certainly take a look at the Miracle-Ducker TL. I am not familiar with the model, but it may certainly work. I've repositioned the '30 wire on the ceiling around the window and will try to run some tests this evening. Will definitely let you guys know how it fairs!

I'll look into the 9:1 transformer set up; that may require drawing up a list with Universal Radio. I was not aware that a Princeton Ham Radio Club existed! But thanks for searching!

Best wishes!

 

[ridgescan]

BTW OP whats up with your username anyway:roll:

 

[usukICOMuser]

Haha it's because I'm Swedish, obviously.

Just kidding, of course. I'm American, British, and an ICOM user/fan.

 

[thomast77]

Something alot of people don't realize is that a good ground can make a difference. But your situation doesn't sound like it will be available. You may try a counterpoise. You don't have many options because everything is restricted for you. And with all the metal and rfi I don't see many options for you. Maybe try connecting to the metal enclosure? Can you take some pictures maybe we can get a better idea of what we are dealing with?

 

[nanZor]

As for finding the quiet "hole," I did find one as well last night - the window area. So I repositioned the equipment there to test. The metal window frame seemed to hurt more than help, although it was a good idea in theory. A noise canceler (e.g., from Timewave or MFJ) might do the trick.

Good news - although the frame itself is noisy it appears. When walking the portable near the glass, was there a hole found that you could eventually substitute a short wire perhaps temporarily taped to the glass away from the window frame, maybe somewhere in the middle? The thought here is perhaps to have a short wire in the hole, and then maybe a short run of coax back to the R75 operating position.

Regarding loops, from woebbers' comment I have a feeling that I will eventually have to purchase a proper loop (likely a Wellbrook).

That would be a great option, and I am a big fan of small loops - but remember you may have to rotate it to null the noise - and this null may be in different directions depending on what frequencies you are listening to at the time - I guess you just want to be careful that the loop can actually be rotated where you decide to place it - if it is physically range-limited such as near a wall, you may not be able to obtain a null on the noise.

Too, it's small enough that I may be able to negotiate with facilities to permit its outside installation (perhaps if I obtain a 2nd- or 3rd-story room in the fall). I'll certainly take a look at the Miracle-Ducker TL. I am not familiar with the model, but it may certainly work.

It was mentioned more as an example of just using a short tunable whip that you might be able to mount temporarily in a quiet hole. The cheapest option would be to just use even plain wire as long as it sits inside the hole. Sounds silly attaching only say 4 to 5 feet of wire to an R75, but you gotta' do what you gotta' do. The R75 has plenty of gain to make even this work given the limitations.

It is a pain, but unlike the lucky ones, we have to work backwards - find a quiet hole with the portable. Put as much antenna wire as you can into it without going so large that it crosses into a noise field. Test with AC power vs DC power. Then test different grounding methods. Before buying anything commercial, see how well you can do with just physical placement of a simple short wire and a coax run back to the receiver and expand from there. It isn't the perfect setup, but you just take it one step at a time for improving it once a decent hole is found.

 

[ridgescan]

The Carpet loop indoor antenna by dxzone.com

80/160m Small Receiving Loop by dxzone.com

Magnetic Loop Antenna by ON2BBP by dxzone.com

following quote was copied out of "Ham Universe.com"
IN ROOM ANTENNAS!

In those cases where you can't put an antenna outside or up in the attic, then you can install it in the same room with the radio! They won't be as effective as those up in the attic or outside but will still get more signal to your radio which is what you want.
Simply use your own method to attach a random length wire, up next to the ceiling against the walls...around all sides of the room if possible. One other choice is to push a random wire between the carpet and the baseboard around the walls of the room. You will be surprised at the difference compared to that telescoping antenna that came with your radio. Just attach the antenna to the telescoping rod...don't forget to remove the insulation on the wire at the attachment point!


...not to mention the info here in the RR wiki.