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Author Topic: New station questions  (Read 656 times)
N8XXX
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Posts: 14




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« on: February 28, 2008, 11:05:59 AM »

I am putting a modest station together and have several questions.  First, from left to right- I will have a flat screen computer monitor, radio (857D), tuner (mfj manual) amp (811 or 811h)  all placed close to each other, do you think I will have any electric noise or interference with this setup?  I do have a good ground system installed.

Can I use the smaller RG8X for a jumper between the amp and the bulkhead going outside, or should I start my full size cable after the amp?

I had planed on using a wet can type dummy load through the tuner as antenna #1 and my station antenna as antenna #2.  That way I could tune up the amp to 1:1 vsr (nerves first time amp user).  I was told by a local ham “never use a tuner on a dummy load.  Is that correct?
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K7UNZ
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Posts: 691




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« Reply #1 on: February 28, 2008, 01:03:09 PM »

Hi Dan....

I can help with two of your questions, but the one about the monitor is a "try-and-see" kinda deal.

The smaller coax is fine for your in-house jumpers. In fact, I use both the 8X and 58A/U in mine.

You can use the coax port on the tuner IF it has a coax direct position that will by-pass the tuner settings.  If not, a simple two position coax switch with the tuner input on one, and the dummy on the other will work fine.

73, have fun!

Jim/k7unz
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WW5AA
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Posts: 2088




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« Reply #2 on: February 28, 2008, 01:19:35 PM »

Jim hit the first two right on.

The monitor would be your greatest concern. Many times in the past I have been able to change the screen refresh rate to eliminate noise. Have fun!

73 de Lindy
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WA9AFM
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Posts: 208




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« Reply #3 on: February 29, 2008, 08:51:41 AM »

Regarding the monitor; I presume you already have the flat-screen, but when replacement time comes around, go with an LCD.  

Besides the space savings, the noise problem is solved.  Another plus is the minimum eye fatigue.  Take a look on EBay, you can find some great deals on high quality LCD monitors.
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AA4PB
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« Reply #4 on: February 29, 2008, 04:14:58 PM »

Since the radio equipment is shielded you should find that any noise pickup from the monitor or computer is via the antenna. If the antenna is far enough away from those devices then you'll minimize the noise.

You should start the RG8 cable at the output of the amp. RG8 from the Amp to tuner and RG8 from the tuner to the antenna.

You can leave the tuner between the amp and the dummy load but it may confuse the issue of tuning the amp. The tuner, if it is not set properly, will convert the 50 ohm dummy load impedance to something different and you will be trying to tune the amp into that impedance instead of 50 ohms. It would be better to switch the amp directly into the dummy load for the purposes of tuning. Also consider that your tuner will need one setting to match the 50 ohm dummy load to 50 ohms and a different setting to match some other antenna impedance to 50 ohms.

If you are feeding the antenna with coax, the antenna should present a reasonable SWR (under 3:1) on all bands. If you try to feed something like a doublet with coax on all bands you can have a good deal of loss in the coax due to high SWR on some bands. Remember, the tuner does nothing for the SWR on the coax between the tuner and the antenna. It can only lower the SWR on that short piece of cable between the tuner and the amp/radio. High SWR increases the loss in the coax - the amount depends on the type of coax, its length, the frequency, and the SWR.
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W5CPT
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« Reply #5 on: March 02, 2008, 11:46:56 AM »

You really don't want to tune your amp into a dummy load then TX into the antenna.  The dummy load will get you close, but the final tuning should be into the antenna on which you are going to transmit.  Unless your antenna is exactly 50 ohm all the way across the band (not likely) the tuning will be very different for the antenna and the dumy load.

When I first got my amp I tuned it on a Cantenna and made notes of the setttings for each frequency in the band. I used 3 freqs on 80M, 40M, 20M, & 17M, 2 freqs on 12M and 4 on 10M (I don't use the amp on 30M).  Then I tuned it on dead bands. That is on 80M in the middle of the day and 10M at night. And made good notes on where I finished. I poked the settings into my computer and printed a little card that sits near the amp.  When I change bands, I can refer to the card and get REALLY close on the settings before I ever key down on the amp. A little touch up is all that is required.


Clint - W5CPT
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AA4PB
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« Reply #6 on: March 02, 2008, 03:49:32 PM »

You really don't want to tune your amp into a dummy load then TX into the antenna
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I disagree with that however, I don't think you meant it exactly the way it sounded to me. You surely do want to tune your amp into the dummy load. Then you switch to the antenna and make any necessary fine adjustments.

In the case described there is a tuner so if the tuner is adjusted using low power (no amp) for a 1:1 SWR then the amp (tuned on a dummy load) should play right into the tuner/antenna with little or no additional tuning.

One reason for tuning the amp into a dummy load first is that the majority of tune time can be spent on the dummy load where you won't be putting a signal on the air that can interfere with other stations. Then you need just a short time on the air with the antenna to make a final touch up.
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KB9CRY
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« Reply #7 on: March 02, 2008, 06:51:06 PM »

I had planed on using a wet can type dummy load through the tuner as antenna #1 and my station antenna as antenna #2. That way I could tune up the amp to 1:1 vsr (nerves first time amp user).


Wrong.  You want to tune the amp directly into the dummy load, not via the tuner and it's antenna 1 connection. That would mean that the tuner circuitry is in line with the amp and you don't want that.  You want the dummy load to be connected to the amp/rig direct and not using the tuner.  Does the tuner have a Direct connection?  That's the one the dummy load ought to be connected to.
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WA7NCL
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Posts: 625




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« Reply #8 on: March 10, 2008, 01:56:08 PM »

You might reconsider the "wet" dummy load unless you have the old style PCB type oil in it.  I think that new ones use mineral oil which might be easy to cause to boil or maybe even catch fire if you spend a lot of time tuning up on it.

Just the thought of a can full of oil in the shack would give me pause.

See if you can afford a dry one with a cooling fan.

Oh yes, and I had a buddy who spilled one of those oil filled things.  What a mess!
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KB9CRY
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« Reply #9 on: March 11, 2008, 12:48:49 PM »

Just the thought of a can full of oil in the shack would give me pause.



They are just fine; one should need to continuously be tuning for minute after minute anways.

Personally I run special high temp compressor oil in mine (similar to high temp transmission oil), stuff that we use in the compressors at work.
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