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Author Topic: Preamp Advise 6M  (Read 4678 times)
N0UY
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Posts: 159




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« on: April 21, 2012, 03:20:10 PM »

I am looking for advice on the subject of a preamp for 6 meters.   I have used a tower mounted preamp on 2meters with great success which lasted about 15 years before snow static rendered it useless.

I am now planning to purchase a 6 meter preamp and I am leaning toward the tower mounted type again because of its obvious benefits realising it's known issues or potential problems due to the location.    What is your recommendations on brand based on your experience?  Tower or in shack both.    I have only briefly looked at whats available so will search for used but will most likely have to go with new because used ones just don't seem to come available.

All input will be greatly appreciated.  I have decided to remove all my vhf stuff above 50 MHz to make room for other interests on the tower.   Thanks for your time on this.

Ray   N0UY
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AA4PB
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« Reply #1 on: April 21, 2012, 03:35:34 PM »

A preamp in the shack is only effective if you have a receiver with poor sensitivity or poor signal to noise. With the front ends in today's receivers this is likely not necessary.

A preamp at the antenna can compensate for feedline loss. If you use low loss feedline or don't have too long of a run then the preamp won't be very effictive on 6M. You also need to consider how much external noise is being received by the antenna. A preamp will raise the external noise by the same amount that it raises the signal.


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G8YMW
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« Reply #2 on: April 21, 2012, 05:44:08 PM »

Front-line VHF contester G4DEZ Bryn Llewellyn uses a masthead preamp on 6, OK he lives out in the sticks so QRM is less of an issue.
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73 de Tony
Sent by WW2 Royal Navy signal lamp
N0UY
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Posts: 159




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« Reply #3 on: April 21, 2012, 06:36:15 PM »

AA4PB    Bob,

I agree with you about the in shack amp although, todays Icom 756 Pro 2 has a very good receiver at the HF frequencies.  I feel it is lacking at the VHF stage so some benefit may be had with the in shack model.   The tower amp will compensate for feedline losses and I am only looking for modest  gain maybe 7 to 10 db.  I live in a rural environment so may ambient noise is considerably different than that found in the city.  The cable length is about 250 ft to the shack.      I am well aware of the merits and demerits of preamps but I am still wondering about manufacturers with affordable pricing something short of commercial quality.

Ray
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K2OWK
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« Reply #4 on: April 22, 2012, 09:25:33 PM »

Hello Ray, If your running 250 feet of of coax to your shack. I would definitely recommended a preamp at the antenna to make up for the loss in the coax. A 7 to 10 db preamp should be adequate for this purpose.

73s

K2OWK
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WB6BYU
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« Reply #5 on: April 22, 2012, 09:45:14 PM »

Quote from: N0UY
...I am still wondering about manufacturers with affordable pricing something short of commercial quality.

Did you check out the Hamtronics  preamps?   

www.Hamtronics.com
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N0UY
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« Reply #6 on: April 23, 2012, 03:31:02 AM »

tnx for the link to hamtronics.  they appear at first glance to be receive only applications so I would need to build the sequencer/relay system to go along with it.

The 250 feet of cable to the shack is 1/2" andrews hardline.  Now that the 432 antenna is coming down I will probably switch that to the 7/8" andrews that will now available for 6 meters.  That alone will increase the signal to the shack.  Still would be nice to have the tower amp I could turn on and off as needed.

tnx   ray
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AA4PB
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« Reply #7 on: April 23, 2012, 05:50:04 AM »

Ray, 250 feet of Andrews 1/2 inch heliax only has 1.1dB of loss at 50MHz.
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N0UY
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« Reply #8 on: April 23, 2012, 10:39:50 AM »

Hi Again Bob,

The jumpers at each end have as much loss as the feedline most likely.  The cable has been on the tower for 16 years or so and the top jumpers was replaced about four years ago.  The one in the ground by the house is the original.

To be honest, I'm of the old school vhfers.  If more and more people keep running a KW on 6 meters I'm going to throw the whole works in the woods and leave it there.

Ray
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WB2WIK
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« Reply #9 on: April 23, 2012, 11:05:05 AM »



To be honest, I'm of the old school vhfers.  If more and more people keep running a KW on 6 meters I'm going to throw the whole works in the woods and leave it there.


Why?  I wish everyone on six ran a kilowatt, they'd be easier to hear.

I have no problem with high power on six meters.  I think with 250' of hardline a masthead preamp is a bit of a waste of time.  You're lucky your 2m one lasted as long as it did; the typical operational life of a good masthead preamp for 6m is probably one season that includes lightning.

Bigger antennas (6m vs. 2m, for example) encourage higher lightning discharge static levels that can be damaging.  I'd at the very least use a switching system that latches the preamp in the "bypass" (transmit) mode 100% of the time when not in use.

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G8YMW
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« Reply #10 on: April 23, 2012, 02:03:52 PM »

Why?  I wish everyone on six ran a kilowatt, they'd be easier to hear.

Disagree totally with that statement. Sounds like his ears want sorting.

When my Radio Club started VHF contesting I told the Chairman "Forget HF, you have to think 70 cms" He started off using thin coax on 6 despite me telling him RG213 absolute minimum.
We got a roll of Westflex 103 and put that on 70 cms, 2 metres (In place of 213) and 6. The tower is almost bang up against the shack. The Club station always finishes in the top 10 in the 100 watts category for 6 despite being < 30ft ASL.

Ray You have the hardline there, you're out in the sticks, as one VHF man to another you go for it.

The 1.1 dB loss in your coax works both ways so really its 2.2 dB. I dont know what the losses are for the 7/8 hardline but what some people are not getting is You've already got it so one expense is out of the window
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73 de Tony
Sent by WW2 Royal Navy signal lamp
N0UY
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Posts: 159




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« Reply #11 on: April 23, 2012, 02:24:11 PM »

Hi Tony,

tnx for the opinion.  digging a signal out of the noise with low or no ambient racket is so much more fun than trying to find the attenuator button to cut off somebody tearing up the spectrum down the band.   The antenna system (including the feedline) has always been the only real advantage for us fellows in the middle of nowhere.

Ray
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AA4PB
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« Reply #12 on: April 23, 2012, 05:56:35 PM »

"The 1.1 dB loss in your coax works both ways so really its 2.2 dB"

Not unless you are running some type of passive repeater. Your received signal is attenuated by 1.1 dB and your transmit signal is attenuated by 1.1 dB but they are two different signals - they don't add up.

I just question whether the effort to install and maintain a mast mounted preamp is worth the effort to compensate for 1.1 dB of loss in the received signal on 6M.

Now if the S/N ratio of the 6M receiver is poor then a preamp, even a shack mounted preamp, could help. In the early 1960's the receivers were not so good and it wasn't uncommon to add an external preamp.

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WB2WIK
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« Reply #13 on: April 24, 2012, 09:20:51 AM »

Hi Tony,

tnx for the opinion.  digging a signal out of the noise with low or no ambient racket is so much more fun than trying to find the attenuator button to cut off somebody tearing up the spectrum down the band.   The antenna system (including the feedline) has always been the only real advantage for us fellows in the middle of nowhere.

Ray

That's funny about the attenuator and such.  I'm in a big city and have several very local hams who run 1kW+ on 6m, including K6SMF who's 1/2 mile from me, and never have to use an attenuator.  Nobody causes a racket up or down the band.  I can operate within a few kHz of all these guys, normally, using just a simple 7L M2 beam at 60 feet on my end.

Maybe you have some local guys with bad TX IMD issues.  What kind of receiver are you using?
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N0UY
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Posts: 159




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« Reply #14 on: April 24, 2012, 02:21:55 PM »

What is your recommendations on brand based on your experience?

No one really got into this question that I asked in the original post.

Most wanted to debate the use of a preamp on 6 meters or not.  Then of coarse it took another direction that had little or nothing to do with the original question.  That was my fault.   When I got interested in vhf it was introduced to me as "Weak Signal VHF" which was a far cry from the FM repeater stuff I was so turned off by in the early 90's.

With the advent of 6 meters in these new HF rigs I guess it was only a matter of time that the culture of VHF would change from what got me interested in the first place.  I did work some aurora last night on CW which did net me a couple new grids in that mode so that helped to relight the candle for a bit but my interest here is dwindling fast also.

I will not be replying to anymore posts or comments regarding this subject on this forum.

Ray
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