Desktop discone?

[jon_k]

Greetings,

I'm wondering if it would be possible to build a discone that would fit on a desktop that would be capable of picking up 2 meters, 440mhz, 800mhz.

No room at work inside, and impossible outside with the place I work at. The building is a warehouse-converted-into-computer-datacenter with cinderblock walls. Our offices are surrounded by the datacenter. The roof is made out of metal. As you can imagine, the walls block out plenty of RF -- and the datacenter surrounding my office adds to the RF (in a negative way.) I practically work in a faraday cage. No windows.

If a discone could be tuned that could fit on my desk, that would be EXCELLENT to help me pick up signals as much as possible. I'm thinking a discone would be the best bet aside from a directional. I'm concerned that if I build a small desktop discone, it will be more tuned for Ghz range due to its small size. That's what I'm thinking would happen.

Any thoughts?

 

[SAR923]

There's a guy who sells just what you want on e-bay. Do a search on scanner antennas and you'll find it. I can't vouch for how well it works, and it looks more like a quarter wave graound plane to me than a discone, but it's probably worth a shot.

 

[DPD1]

If you have that much blockage, I think your best bet is having something that can be moved around easily to hopefully find a sweet spot. Even if that means hanging it from the ceiling. I'd go with maybe a Diamond RH77 or RH951 on one of those little coax lines with a clip on the end.

Dave
www.DPDProductions.com
Antennas & Accessories for the RF Professional & Radio Hobbyist

 

[zz0468]

A discone that's usable down to 2 meters is going to be the size and shape of a medium lampshade, only heavier. So it won't exactly be convenient on the desktop. Come to think of it, a modified lampshade might just make an excellent stealth discone, if someone was skilled in fabrication.

 

[jon_k]

If you have that much blockage, I think your best bet is having something that can be moved around easily to hopefully find a sweet spot. Even if that means hanging it from the ceiling. I'd go with maybe a Diamond RH77 or RH951 on one of those little coax lines with a clip on the end.

Dave
www.DPDProductions.com
Antennas & Accessories for the RF Professional & Radio Hobbyist

OK. I just purchased the RH77CA this weekend, and it should arrive later. I'll give this a try before experimenting further. It may be possible to find a sweet spot.

Please note, I /do/ get signals with the Radio Shack 800mhz antenna. I get signals less so with the stock ducky. It isn't as bad as the picture I draw in my original post -- but my reception definitely isn't on a mountain top.

I'm just trying to open myself up to better reception despite the poor location I work in. 2 meters and up (144mhz and beyond.)

 

[andrewccm]

Hard to beat that RS800 for 800mhz... I have tried all kinds of things too..

 

[n5usr]

Just in case you haven't thought about this, how is your building cooled? Most like you describe that I've seen use rooftop units, which can often offer a route to run a cable without making new holes.

If you happen to have one above the area you work, and you can get permission to do so, you may be able to run a coax down in a variety of ways - with the thermostat cable, alongside the conduit feeding power up if it enters through the bottom of the unit, or if the unit is "plenum return" (meaning it has no ductwork on the return air side) just right through the return air opening then out through the outside air damper opening (but be careful of moving parts here). Find an opening to get the cable outside, then just stick a mag-mount on top of the unit - they make nice ground planes.

Warehouses usually have a pretty tall roof, if that's hidden behind a dropped ceiling in your work area, you may be able to avoid needing a tall ladder by dropping the cable down from the unit, securing it well in the unit, and just letting it hang below.

I did this at my last workplace, when I was stuck in a desk job for a while. Worked very well indeed! (Of course, I work with HVAC control systems so me being on the roof and running cables wasn't too out of the ordinary! )

 

[jon_k]

Just in case you haven't thought about this, how is your building cooled? Most like you describe that I've seen use rooftop units, which can often offer a route to run a cable without making new holes.

If you happen to have one above the area you work, and you can get permission to do so, you may be able to run a coax down in a variety of ways - with the thermostat cable, alongside the conduit feeding power up if it enters through the bottom of the unit, or if the unit is "plenum return" (meaning it has no ductwork on the return air side) just right through the return air opening then out through the outside air damper opening (but be careful of moving parts here). Find an opening to get the cable outside, then just stick a mag-mount on top of the unit - they make nice ground planes.

Warehouses usually have a pretty tall roof, if that's hidden behind a dropped ceiling in your work area, you may be able to avoid needing a tall ladder by dropping the cable down from the unit, securing it well in the unit, and just letting it hang below.

I did this at my last workplace, when I was stuck in a desk job for a while. Worked very well indeed! (Of course, I work with HVAC control systems so me being on the roof and running cables wasn't too out of the ordinary! )

The company I work for leases office space from the datacenter who hosts about 14,000 machines for us. We pay them about $300,000 a month. The people who run/maintain this facility aren't very cool people. In fact, there is no air conditioning in our office, and they installed a bathroom fan as a fix, claiming that our workstations (3 machines with 6 monitors) generate too much heat, and that their offices are just fine.

Temps rise to 85 degrees during peak and the owners of the facility are jerks. They don't mind spending money on 1/2 ton cooling units for the datacenter, but they won't fix our office. (Unsure why our CEO hasn't complained, perhaps because the actual business office of our company is in another location (that is cooled!) where he works.)

Suffice it to say, the owners of the building won't let us install a portable A/C unit to keep our working conditions outside of sweatshop standards. Let alone run some coax.

Sorry for the rant. I'm 10 hours in out of my 12 hour shift overnight -- and I've got 2 inch pit stains so I'm irritable right now.

 

[Don_Burke]

I would look into a couple of coaxial antennas with a common feedpoint.

The footprint would be much smaller.

 

[scannersnstuff]

not to go off subject but you may want to look into the possibility of a osha complaint about your working condition's.if i'm not mistaken,a employer must maintain certain temperature standard's for it's employees's.while i am not an expert on the subject,look into it and find out.you may want to file your complaint annonymously.

 

[jon_k]

not to go off subject but you may want to look into the possibility of a osha complaint about your working condition's.if i'm not mistaken,a employer must maintain certain temperature standard's for it's employees's.while i am not an expert on the subject,look into it and find out.you may want to file your complaint annonymously.

Definitely. My employer isn't responsible for this, but the owners of the building are, which would be liable themselves.

I think I'm going to build some directionals that point in 4 directions and try that.

 

[Bill_White]

Diamond Mini Discone:
http://www.universal-radio.com/catalog/hamantm/0312.html