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Author Topic: RG8X or LMR-240  (Read 5117 times)
KD8TFG
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Posts: 65




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« on: September 27, 2013, 06:49:22 PM »

We just recently moved into a townhouse from our old duplex and will be putting up my A99 Vertical 10ft in the air same as our old residence ( restrictions with property mgt. on height) running an Icom 730 and MFJ-949 tuner, at the old location I had a 25ft run of rg8x and our new location will be around a 50ft run. My ? is it worth the extra cost to run lmr-240 or just buy rg8x again.

The A99 will tune to about 1.3 to 1 on 10-20m with full out put and will tune up on 40m about 2 to 1 with about 50w out.

So which would you run in my given situation ?

73 Gary
KD8TFG
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W4OP
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Posts: 393


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« Reply #1 on: September 27, 2013, 07:12:10 PM »

Look up the specs for each cable and you can then see what the matched attenuation is for each cable.
Be aware though, if you are using a tuner to achieve low VSWR at the rig:
1. The tuner has some loss- the amount depends upon the topology, components etc
2. The tuner does nothing to lower the VSWR on the feedline- so you will have increased loss on the coax (reflection or mismatch loss) over and above the matched loss. The only way to negate the reflection loss is to have the tuner located at the antenna.

Dale W4OP
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N8DXB
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Posts: 12




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« Reply #2 on: September 27, 2013, 10:38:50 PM »

Gary, I would pitch the RG8X and go with the LMR or Belden 9913F7, and not use the tuner at all unless it is really needed. I did a test on the RG8X years ago and I did not like the loss.
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K2OWK
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Posts: 1037




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« Reply #3 on: September 27, 2013, 10:51:48 PM »

Hello, To answer your question the RG8X should work just fine for runs of 50 feet or so on HF (160 thru 6 meters). I have three antennas one is an 32 foot S9 vertical Fed with about 40 feet of RG8X using a 4 to 1 UNUN. It works great. The next antenna is a 40 meter inverted "V" Fed with about 50 feet of RG8X. It is an NVIS antenna and works great for its intended use. I also have an Arrow dual band 2 meter/.70 CM using RG8X, about 25 feet. This antenna hits all the repeaters out to 40 miles or so, more then I need. To check losses look at the specs for each cable, you will find the losses for RG8X are minimal for the runs you are talking about. My 2 meter/.70CM run has a little more loss's, but also not very worry some at the short run lengths.

Hope this helps.

73s

K2OWK
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VE3WMB
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Posts: 282




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« Reply #4 on: September 30, 2013, 04:26:55 PM »

If you are already planning to use a tuner why not consider using RG-6U ? Most RG-6U is as good or better
at HF frequencies as RG-213. The fact that is is 75 ohms will introduce a slight mismatch but the tuner
can take care of that. I got 500 feet of a decent quality RG-6U for around $70 at The Home Depot.

Michael VE3WMB

We just recently moved into a townhouse from our old duplex and will be putting up my A99 Vertical 10ft in the air same as our old residence ( restrictions with property mgt. on height) running an Icom 730 and MFJ-949 tuner, at the old location I had a 25ft run of rg8x and our new location will be around a 50ft run. My ? is it worth the extra cost to run lmr-240 or just buy rg8x again.

The A99 will tune to about 1.3 to 1 on 10-20m with full out put and will tune up on 40m about 2 to 1 with about 50w out.

So which would you run in my given situation ?

73 Gary
KD8TFG
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N4KD
Member

Posts: 131




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« Reply #5 on: October 01, 2013, 05:40:29 AM »

For a resonant dipole, that's a completely true statement. It's mostly true for any 50 ohm load, with a little explanation in order.

If you have an antenna with a 50 ohm load, the RG-6 acts as a matching section. At electrical half-wave lengths, the impedance is repeated at the rig. That's right at 1:1 for a 50 ohm load (antenna). At 90 degrees of electrical length, the voltage and current are out of phase at the end of the quarter wave (or odd multiple). But now we can answer the question, "What's the worst case match?" The wavelengths will vary, but at 90 degrees, the mismatch will always be around 2.25:1. That means you lose about 18.5% of your power due to return loss.

So, yes, the tuner will make a 1:1 match at the rig, but there will also be some loss in the line. Not enough to worry about, though. I'd buy the RG-6, or in another situation, look for some CATV hardline.

If you are already planning to use a tuner why not consider using RG-6U ? Most RG-6U is as good or better
at HF frequencies as RG-213. The fact that is is 75 ohms will introduce a slight mismatch but the tuner
can take care of that. I got 500 feet of a decent quality RG-6U for around $70 at The Home Depot.

Michael VE3WMB

Vy 73,
Dave N4KD
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W5WSS
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Posts: 1652




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« Reply #6 on: October 01, 2013, 01:16:22 PM »

Can you consider a remote tuner near the feed point?

LDG has designed a 100 watt pep remote located yet remote controlled switched L automatic water proof version tuner that can be mounted on the pole just underneath the feed point in this case, the A-99 and would be possible with their mounting hardware.

The antenna is a very nice length for 20-10m elevated vertical work. A common mode choke located adjacent and close and between the antenna feed point and the tuner would be advised with the A-99 to help isolate the antenna from the coaxial feed line shield.

The system when done that way will avoid feed line losses caused by sever mismatch and rather operate the entire antenna feed line into a 52 ohm non inductive condition as a matched line since it can be placed in the tuned zone found between linking "the tuner and the equipment together."

73
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N6AJR
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Posts: 9890




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« Reply #7 on: October 02, 2013, 10:30:58 AM »

it will work OK with the rg 8x, but if you can afford the extra $$ the lmr 240 or any cable with better "stats" than the rg8x will alwayss be better, but it may not be enough to notice the difference.
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N4LPK
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Posts: 3




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« Reply #8 on: October 31, 2013, 12:14:28 PM »

I am running a 75' run of RG-8X to a ZS6BKW/G5RV and my SWR hasn't exceeded 1.3 to1 on the resonant frequencies of this antenna.  I use the tuner in the radio for the bands not covered and 1.3 to 1 is the highest it has ever been. Now I am running only 100 watts and the center feed point is at 41 ft with the wire in an inverted "V" at twenty ft. off the ground.  I recently worked the Czech republic and the Canary Islands with this setup with no issues. I worked the Czech Republic on 15 meters which I have to tune for and it worked fine.  Now that being said runs over 100' probably I would go with the LMR 200 just to play it safe.  Just my 2 cents.
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K1WJ
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Posts: 451




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« Reply #9 on: October 31, 2013, 02:58:36 PM »

A99 is 10m/11m antenna, coax loss at 28mhz will be more v.s 40m-80m. 50ft is a short run, both will work fine, but if your looking to have as little loss possible 9913 would work better, & 9913 is also very good on vhf/uhf. I would not expect the a99 to work good below 17m. I do not like non-resonate antennas with tuners in general. 73 K1WJ  Cool
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KA5N
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Posts: 4380




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« Reply #10 on: October 31, 2013, 04:16:37 PM »

You can find "computers"  in most ads for coax where you enter the type coax, length etc and
they will calculate the loss in the coax.  Only takes a few minutes.  So you would check the
loss of RG8X and then the LMR-240  (or whatever)  if the loss in the line is a half dB or so
don't worry.  If in the 2 dB or higher range then start looking for something better.  Of
course the really good stuff costs more.    I use about 35 feet of RG8X and only rarely note
any problem (most problems are due to QRN or weak signals).

Allen KA5N
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KD8TFG
Member

Posts: 65




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« Reply #11 on: October 31, 2013, 06:18:57 PM »

A99 is 10m/11m antenna, coax loss at 28mhz will be more v.s 40m-80m. 50ft is a short run, both will work fine, but if your looking to have as little loss possible 9913 would work better, & 9913 is also very good on vhf/uhf. I would not expect the a99 to work good below 17m. I do not like non-resonate antennas with tuners in general. 73 K1WJ  Cool

I ended up using the rg8x with very good results, the A99 performs very well on 10/12m with tuner bypassed and 15-20m with the tuner in line works great made an 8800mile contact on 20m during the world wide cq contest and the A99 is only 10ft in the air in fact it performs very well on 20m (how I do not know but not complaining)it will tune 40m and have made some regional contacts but am not interested in 40m at the moment
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