briskattivo
Member
- Joined
- Mar 29, 2016
- Messages
- 39
What would be the alternative?
After experimenting with this for a couple of weeks, I'm regressing in that I now believe the majority problem has to do with my attempt to listen to a wider distance with a simple VHF tuned duckie or an RH77CA more than it does my computer. I found a couple of streams of local radio bands I had been trying to listen to, including rail, and the amount transmissions I picked up on my radio compared to stream was minute. My scanner does, however, work great for police/fire/ems and other trunked systems, which is good because I love listening to those. I will invest into a more serious antenna in the future. And it wasn't all in vain as I got this sweet Lian Li 7B-Plus II case out of the experimenting. It was very interesting to try and troubleshoot, so thank you!
Here is one more thing to try that may improve your situation. Make a simple BALANCED antenna to minimize conducted noise from the cabling and ineffective grounding from entering your antenna system. This is like the twin lead antenna provided with home stereo receivers, but will be electrically shortened and need to be matched to your 50 ohm receiver with a BALUN transformer like used on TV sets. It will also need to be installed vertically, and the feed line (also 300 ohm twinlead 4 to 6 feet) should be strung horizontally away from the dipole to minimize interaction and coupling.
For materials you can simply buy a commercial FM dipole and cut it length.
http://www.amazon.com/Parts-Express..._UL160_SR160,160_&refRID=0XF6MBCVMHZ7QFXRV5B8
1. Make a 1/2 wave dipole antenna from 300 ohm twinlead.
The formula for a center fed one-half wavelength (in inches) is 5,616 divided by the frequency (in megahertz) x the velocity factor of the twin lead 0.82. so 5,616/160.8375 = 34.92 inches X 0.82 = 28.63 inches.
http://www.avsforum.com/forum/attachment.php?attachmentid=656713&d=1428579867
Start with the length of 35 inches center fed at 17.5 inches and once you have it installed (vertically) shorten the arms by up to 3 inches each to improve reception if necessary. Having an antenna analyzer would help. Personally, w/out the analyzer I would try it out "long" and see how it works out.
2) Connect to your receiver via a 300 ohm to 75 ohm BALUN transformer:
http://www.amazon.com/300-Ohm-UHF-Matching-Transformer/dp/B0002ZPIOG
3) And a BNC to F adapter of the appropriate sex for your cabling:
BNC F Adapters - Monoprice.com
The antenna as-is is cut for 88-108 MHz, probably optimized for about 98 MHz so you will need to cut to dimensions calculated for the rail-road band. As far as VHF air band, you could try it as is, but would be best cut to a frequency midway up the air band. These dipoles are cheap so you could make two and use a cheap TV coax switch.
To connect the transformer to the dipole, you could use small nuts and bolts, but be sure to keep them separated close to the the width of the 300 ohm twin lead. Another way are those barrier strips used for electrical connection that have screws already in place.
When you get it up, make sure the dipole is vertical and the twin lead feed line extends to the side at a right angle on the wall as much as possible so as not to influence the dipole.
Received all parts today. Assembled, and yeah! Airband is like the difference between night and day. That is as is. I'm talking constant stream of readable transmissions. RFI-EMI-GUY you are the best! I suppose I will order some more duplicate orders so I can experiment on railband and airband with measured dipoles. I'm serious though, this is really cool. For the record I ended up using a combination of motherboard landing nuts and bolts and electrical tape on the hook connectors. Seems to have worked. I'll reply with an update when I try a railband dipole. Feeling a bit cautious to try and cut down my only dipole down to a measured length for airband when it already seems to be working so well, so I'll wait until I get one more for that too.
Glad that's working out. Let me know if the rail band cleans up!
19" is right for 2M ham. Railroad will be a little under 18" - 17.5" sounds about right.
Airband will be around 19" or maybe a little more depending on the part of the band you want to target.
You should be fine. Some antenna designs actually mismatch the elements slightly to get more bandwidth.
It seems that you have tried about everything while also keeping your good video card.
One thing I may have missed seeing in your posts is the video cable itself.
Have you tried a better quality video cable?
Or simply switching from DVI to VGA or the reverse just as a test to rule out the video cable as a noise source?
I've had the same issues as you and if not from the video card itself, I've found both the type and quality of the video cable to be the source of noise.
As several have also mentioned, the power supply itself but it seems you have tested that very well using different supplies.
I once had a brand new Antec supply that killed DSL signals back in the DSL days. And yes, it also wiped out my HF monitoring as well as low band and a good chunk of VHF High band.
Finding and curing EMI/RFI noise sources can be a major challenge but also fun depending on how you look at it.
One other thing to look at is ground loops if not all equipment is not powered from the same source. Sometimes a decent isolation transformer can cure that but high current ones can get expensive.
I have several months of time devoted to finding and curing sources of noise getting into my radios. Way to much to list here but in the end, it worked and was well worth the huge amount of time, effort and money I invested in it all. I'm virtually noise free from DC to Daylight now!