On the bandwagon: RS Coax is crap

[KC2UGV]

Ok, I'm on the band wagon now. Rat Shack Coax is crap, for VHF.

I've not had a problem ever with my digi node. So, I get the antenna in place, and fed with rat shack coax.

Now, it stick on PTT. I came home last night to find my node on constant TX, hotter than a witches tit simmering in hell. Must have been keyed up for at least an hour :roll:

So, I disconnected power, let it cool for about 1.5 hours, and tested it again. Sho-nuff, stuck on transmit again...

Well, on to Hirch's for some cable...

[NQ6U]

What kind of coax was it--RG-8U, RG-58, etc? I found that switching my VHF cable runs to LMR-400 (with Type-N connectors) made a noticeable difference.

[KC2UGV]

What kind of coax was it--RG-8U, RG-58, etc? I found that switching my VHF cable runs to LMR-400 (with Type-N connectors) made a noticeable difference.

58... I don't think they carry anything but. Yeah, it's time to break down and get some good coax and connectors now, because at this time, my digi is still offline to prevent problems.

[NQ6U]

Yeah, good idea. The attenuation of RG-58 at VHF frequencies is horrendous and, of course, that loss is translated into heat. If you can't afford LMR-400 or something similar (try eBay, I got a good deal on some there), at least switch to RG-8U. It's still pretty bad at VHF frequencies but it's better than RG-58.

[KC2UGV]

Yeah, good idea. The attenuation of RG-58 at VHF frequencies is horrendous and, of course, that loss is translated into heat. If you can't afford LMR-400 or something similar (try eBay, I got a good deal on some there), at least switch to RG-8U. It's still pretty bad at VHF frequencies but it's better than RG-58.

Well, it boils down to a combination of the following, most likely:

* Shit poor coax for VHF
* New Antenna (And, common mode issues)
* Antenna too close to transmitter

When it was last set up, I was using Belden Coax (8410, I think. TV coax). It worked very well. However, the antenna was a groundplane 1/4 wave; and it was located about 15 ft away, as the crow flies.

Now, I'm using RS RG-58 coax, it's a vertical dipole, and it's only about 3 feet away.

I don't think common mode (I'm not hearing anything on a crap set of speakers nearby, my du jure test for common mode issues), so I'm guessing leakage from the cable, locking the PTT serial line. Or, direct coupling of the PTT control to the antenna, keeping it keyed up.

[KG4CGC]

58 is crap for most things. Back in the day, even their RG-8 was a crapshoot but they did carry better material just before it was phased out of their stock. RS stuff is the only brand that I've seen that the braid tarnishes. This means there are large enough openings in the outer cover to let in abundant air and maybe water.

[ka8ncr]

If you're nice, you can get LMR-400 from Hutton for well under a buck a foot. Ask the sales guy for odd lots and they're happy to unload it, just be prepared to buy 30' or 223'. Times Microwave has a crimp N for that cable that is truly heavenly.

Seeing that might be a bit rich for some hams, there's Comscope RG-11. It's 75 ohm cable, but I've used it for VHF and UHF and it worked fine. That stuff is cheap.

[kd8dey]

Been using lmr-240uf myself for VHF/UHF

dunno how good this stuff is BUT I have been wanting to give it a try

http://www.copper.com/cart/product_info.php?cPath=39_73&products_id=1429

[PA5COR]

75 foot runs here up to the Diamond X 510N, or to the 11 element Flexa yagi for 2 and the same for the 23 element flexa 70 cm.
Ecoflex 15 ( mm) or about the same as LMR 600.
In the van 8 feet Aircell 7 ( mm) very low loss.
For the vertical L 160-20 meter antenna Aircell 7 40 feet to the tuner MFJ 998, running 1 KW through it.
Rest of the coax on HF-6 is Aircom plus, the same as LMR 400.

All N connectors.
The EWE antenna Aircell 5 just recieve.
I don't skimp on coax or connectors.

[W5GA]

Ratshack RG-8 is the only coax I've ever seen flash over with high power on it.

[KG4CGC]

RG-6Q for VHF, opinions?

[kd8dey]

RG-6Q for VHF, opinions?
75 ohm around 50 cents per foot (discounted)
Attenuation dB/100m
50mhz 4.8
200mhz 9.7
can't find a power rating
Meant for CATV/SAT
I wouldn't go out of my way to buy it But if I already had it on hand I might try to find something to do with it. Scanner feedline or something.

[KG4CGC]

75 ohm around 50 cents per foot (discounted)
Attenuation dB/100m
50mhz 4.8
200mhz 9.7
can't find a power rating
Meant for CATV/SAT
I wouldn't go out of my way to buy it But if I already had it on hand I might try to find something to do with it. Scanner feedline or something.
Got a bunch of it when we redid the CATV lines. Stuff the cable company uses. Didn't care for it much as a receive conductor but then again I was comparing it to the Conundrum 80.

[n2ize]

hotter than a witches tit simmering in hell..

I thought a witches tit was cold ??

[n2ize]

Well, luckily for me on HF I don't use coax. For a while I had a 2 meter beam on the garage roof fed with old rat shack 58/u co-ass and it seemed to work good but, I was running no more than 5 watts into it. For a while I was using that same coass on HF feeding a HF vertical on 10 metres. After a long keydown with anywhere between 100-325 watts it would feel a slightly warm to the touch. On HF I generally try and avoid using co-ass cable. I much prefer balanced line.

[ka8ncr]

75 ohm around 50 cents per foot (discounted)
Attenuation dB/100m
50mhz 4.8
200mhz 9.7
can't find a power rating
Meant for CATV/SAT
I wouldn't go out of my way to buy it But if I already had it on hand I might try to find something to do with it. Scanner feedline or something.

I've used it for scanner feedline, and I used it for AO-51 out of the S-band downconverter.

[W7XF]

Jeebus.... I wouldn't trust jack shit from CellPhoneShack anymore. I can probably get better quality RG-6 at WalMart than RatShack's RG58. If I need RG58 THAT bad...I'll just go to the truck stop. Never had a problem with truck stop 58 or 8X.

[KG4CGC]

Jeebus.... I wouldn't trust jack shit from CellPhoneShack anymore. I can probably get better quality RG-6 at WalMart than RatShack's RG58. If I need RG58 THAT bad...I'll just go to the truck stop. Never had a problem with truck stop 58 or 8X.
Truck Stop RG-8M is good but the price you pay is close to triple. Had to have some at 11:30pm one night and I was 5 miles from that notorious Pilot at exit 35 on Hwy 85.

[NQ6U]

Truck Stop RG-8M is good but the price you pay is close to triple. Had to have some at 11:30pm one night and I was 5 miles from that notorious Pilot at exit 35 on Hwy 85.

Hey, Charles, I've been to that Pilot!

[KG4CGC]

Hey, Charles, I've been to that Pilot!

http://www.youtube.com/watch?v=MmFN9C9PVpg
http://www.youtube.com/watch?v=MmFN9C9PVpg

[WØTKX]

http://vk1od.net/transmissionline/RG6/index.htm


RG−6/U happens to be the lowest cost cable and it has loss comparable with the most expensive cable in the group, being RG213.http://vk1od.net/transmissionline/RG6/Fig02.gif


Voltage breakdown is near instantaneous, and operating voltage is higher with VSWR>1. Nevertheless, for most applications, voltage breakdown is less limiting than overheating. The breakdown voltage of RG−6/U is typically around 2.7kV, which would be reached at a power level of nearly 50kW in a matched 75Ω system.



Voltage breakdown is an instantaneous effect and so limits the peak power at which a cable may be operated. Because of thermal inertia, the cable temperature increases as a result of power averaged over time. The duty cycle (transmitter on / transmitter off cyle) and modulation type may reduce the average power for a given peak power.

For example, considering only the modulation type, the peak to average ratio for compressed SSB is about 15dB, for a factor of about 30. Considering again the example of RG−6/U at 7MHz is 1580W with VSWR=1, it would withstand 30*1580W or 47kW of SSB telephony from a thermal limit perspective, but for A1 type Morse code with a peak to average ratio of about 2.2, the thermal limit would be 2.2*1580W or 3.5kW.

If the period of on/off duty is short compared to the thermal time constant of the cable, duty cycle can also be considered in rating the cable for the specific application.

[N8YX]

I've used it for scanner feedline, and I used it for AO-51 out of the S-band downconverter.
Same here. I plumbed the whole house with the stuff - a power divider with preamp services the upstairs scanner bank, and a feed from that is run into the main shack where another power divider and line amplifier are used to feed the various receivers.

There are 8 in total in the shack and 5 scanners in the upstairs area. One of these days I'm going to get hold of another PRO-2096 for use in the secondary listening spot.