InterceptRadio.com Forums

My setup.

2x BC246T scanners
Discone Antenna. Freq range 25 to 1300. (dont know the brand)
RG8 cable. Apx 55 foot run.
Radio Shack 800Mhz scanner antenna.

Ok. So I installed my discone antenna on top of my roof. Ran the RG8 to inside my place. Short version of a long story, the 6 inch Radio Shack 800Mhz antenna has better reception than the discone on top of my place.

No shorts in the RG8 and I had a friend use his 2meter radio to transmit/recv on. The discone antenna way outperformed the ducky antenna he had. So, that tells me again the cable and antenna are installed ok.

So... Is it possible that the little RS 800Mhz antenna can out perform the large discone antenna simply because it tuned for 800Mhz?

Being Sno Co. is all 800 now. Any recommendations on a good 800Mhz antenna for my roof? Or perhaps a good quality discone antenna?

Do you live on a hill or below? Is there a lot power lines? How far do you live from the repeater?

Yup. I'm in the Picnick Point area. Which is kind of down in a hole. No power lines. I'm trying to listen to the King Co. Trunk. Specific Valley Com.

before you spend a lot money. Take the scanner and clamb up on the roof to if you pick it up. You might wan to use the 800 ant for the test. If pick up a c/c on 851.8125. You got King County and Valley Com. Where you pick it up at mark it on the roof with something the install a big ant. there.

Already did that. No matter where I am around my house, the ducky 800 antenna outperforms the discone on the roof.

You might want to program in all the freqs for KC TRS it might use another c/c freq up there.

Thanks. But I want to be able to put an antenna on top of my house and have it work better than a small Radio Shack ducky antenna. The problem has to be with the discone antenna. Well, not problem but I've come to think that any tuned antenna will kick butt over a discone. Just the way it is. I think?

The discone is broadbanded, good for all around but not specific reception. I live 60 miles south of Seattle and use the GRE pre amp in conjunction with the RS 800 antenna. If you can live with switching antennas, just for the 800 reception then the 800 duck might be as good as it gets if the reception is "ok". 800 is tricky to capture as compared to VHF and UHF. I tried a 800 yagi and my results wern't much better than the RS product.

Well. I bought this antenna today. I hope because it's tuned for 800Mhz, it's going to make a big difference.
http://cgi.ebay.com/ws/eBayISAPI.dll?Vi ... &rd=1&rd=1

I hope I can help with your problem.

I agree that the discone antenna is a compromise, it is unity gain at best, meaning 0 gain. It does offer wide band reception, but not as good as a band specific antenna. It's great for wide band searching if you have access to a band specific antenna for real world monitoring.

Your friend had success with a two meter 144-148 MHZ radio because of the line loss related to the rg-8 cable. The higher the frequency the more the loss. Check out this site http://www.timesmicrowave.com/cgi-bin/calculate.pl it shows the loss associated with the different coax cables by type and length of the run.

Keep in mind the more adapters you use, the more the loss. Google this concept and you will find a lot of information.

Just a quick side note the "radio ripoff site" is wrong as far as frequencies go ( as well as many talk groups) Intercept is much closer to reality. I see so many people on this forum link to un-verified information on frequencies, especially "radio ripoff". Please don't post information unless you have verified it personally.

Bottom line is the Comtelco antenna you purchased will more than likely outperform your discone, but the coax will limit the improvement. I suggest LMR-400. Try the calculator and you will see the difference. You need to put an N connector at the antenna and then do what it takes at the radio.

Bottom line is I can see the RS rubber duck doing better than the unity gain discone with high loss rg-8 coax which is designed for HF use.

Hope this helps.

Vince.

Vince.
Thanks for the info. And I'm well aware of the line loss in RG8. And I used that online calulator to get my numbers. My run is about 55 feet. Which is about 3.5db of loss. With LMR400 that will drop to around 2.

However, I do not think Line db loss is the issue here. I went on to my roof with my two BC246T radios. I connected one radio to the discone using a 2 foot length of RG58. The other radio had the RS 800 ducky. The ducky still out performed the discone.

In addition, I did not see any noticable difference between the reception when I was on the roof connected to the discone opposed to inside my house using the RG8 run. And yes I swapped the radios, the issue stayed with the discone antenna.

Band-specific antennas will always work better than a broadbanded antenna at 800-900mhz. This is because most 800/900mhz antennas are collinear and produce a few dB of gain despite their small physical size. I hope the Comtelco antenna works good for you. The engineer behind Comtelco is Bob Scorza (K9FRM). I've had real good success with his products. He also makes the best super low loss NMO-style mobile mount for 800mhz-2.5ghz. Part number is CEZM-02.

http://www.comtelcoantennas.com

Thank you for all the info. This all seems to confirm what I had suspected.

Ok. One last question. I've decided to replace the cable. I am for sure going to use at least LMR-400, however if I can I would like to use LMR-600. Does anyone know if there are solder PL259 connectors for LMR-600?

I doubt you'll pick up more than 1 dB or so (at 800mhz) by switching from 400 to 600 on a 55-foot run. Its really not worth the hassle of dealing with a cable which is more expensive, less flexible, and more of a pain/expense to put connectors on. If this was my setup, I'd run LMR400 with some decent quality N-connectors on both ends then use a short 2-foot jumper (N to 259) of thinner cable to the radio. One problem with heavy cable like LMR400/600 is it can put too much mechanical strain on a chassis-mounted connector on the radio.

My personal rule is not to mess with cables/antennas unless there is at least 5 or 6 dB to get out of it.

Ok. Sounds good.
Ya. I've already got a setup so the cable does not put stress on the radio connections.

LMR400 with 800 tuned antenna. THats the ticket.

I'll report back my results in a week or so.