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Author Topic: Opinions on 6M FM Repeater Wanted  (Read 578 times)

N4DBM

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Opinions on 6M FM Repeater Wanted
« on: January 06, 2021, 04:42:06 PM »

Hi,
I've been an active ham since 1988 but have limited experience on 6-meters. What bit of 6-meters I have done in the past was point to point SSB, horizontal. 20+ some years ago I did successfully get a repeater running with a BP/BR duplexer and single antenna with good success, as I remember, but can't exactly remember how good that success was.

Recent acquisition of some commercial low-band equipment that converted easily to 6-FM has inspired me to get something up and running again as a remote base or duplex repeater since I have access to the duplexer and the antenna and radio hardware is available.

I have a DB-201 folded monopole (basically a ground plane) up at 400 feet, top mounted and cut for 52.5 MHz. It matches perfectly and is unobstructed and out in the clear. There's about 480 feet of 1/2 inch cable feeding it with about 2.2 dB of loss. The terrain where I am is flat, no hills whatsoever. The base transceiver at the site is a Motorola CDM1250 at 60 watts with noise blanker enabled. The noise floor at the site is okay, not great but not as bad as being in town. The site is located in a remote area.

The mobile radio is another CDM1250 with a 48" NMO whip, properly series loaded for good match. TX power is also 60 watts.

The base radio is "cross connected" to a local UHF repeater in which I can communicate from the mobile through the 6-meter cross band over to UHF for test purposes. With the tests I have been running for the past few days, I am perhaps a little disappointed with the coverage. The 2-meter machine at the same site, granted is running about 8 dB more ERP, out-covers 6-meters by 10 miles or a little more. The 2-meter machine covers around 40 miles in every direction. I can get 30 miles with the 6-meter at the same height.

I understand that atmospheric noise is an issue with 6-meters. The commercial world has obviously fled low-band due to this and other things. I also know that a 1/4 wave folded ground plane doesn't focus the RF toward the horizon like one would want, but it was the most robust thing I had to mount out the top of the tower.

What I am looking for is other peoples' opinions on how 6-meter FM performs in other areas. Does it cover better or worse than 2M, or 220 MHz at the same location as far as pure reliable distance from tower to mobile? Are 6-meter repeaters practical? I am looking toward migrating to a repeater to perhaps stir some activity in my area. What is your experience with 6-meter repeaters?

Any feedback is welcome.

73, N4DBM
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K6AER

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Re: Opinions on 6M FM Repeater Wanted
« Reply #1 on: January 06, 2021, 06:49:43 PM »

I had a 6 meter repeater on Castro Peak, Malibu, CA from 1978 to 1988 in LA county. The repeater was on 52.88/28 Mhz and ran 200 watts from a 6 dB gain vertical gain antenna. Stations worked 49 states but alas Hawaii was never worked.

The duplexer was a WACOM BpBr 6 cavity unit and the repeater was a modified Motorola Micor unit. Amplifiier was a Motorola paging amplifier using a 4CX350 tube for the paging unit.

Repeater was located above Malibu at 3000 feet. It was not uncommon to hear mobile from 3000 miles away using the repeater on a daily usage.

The ground wave coverage from the site covered well out to 150 miles. A lot of this was a result of inversion bounce that is common in the summer months in Southern California. We would have coverage from Sana Barbara to San Diego.


Six meter noise floor was never a problem. Typical receiver noise floors were in the neighborhood of .2 uV. If you are experiencing noise floor higher than that it might be a local interference problem.
« Last Edit: January 06, 2021, 06:54:39 PM by K6AER »
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N4DBM

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Re: Opinions on 6M FM Repeater Wanted
« Reply #2 on: January 06, 2021, 06:56:40 PM »

Thanks for the reply.  My noise floor at the site is over 1 uV.  But then again the noise floor in the vehicle just driving around is 1 uV on average as well.  The receiver when going straight into the signal gen is around 0.5 uV for 20 dB quieting.

That's amazing performance on 6M that you had.  I would have to attribute at least some of that to the noise floor being much lower in the years you operated the machine.  With some sort of microprocessor running all around us, the entire noise floor has increased quite a bit over what I remembered it being 25 years ago..
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W5OT

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Re: Opinions on 6M FM Repeater Wanted
« Reply #3 on: January 06, 2021, 08:26:37 PM »

KA7LFX has a 6m repeater on top of Mt Lemmon near Tucson, AZ.  Granted, it's at 9000+ ft, but there is a weekly saturday night net run on it.  The net control is a ham out of Phoenix (120 miles away), and most of the traffic is from the Phoenix area.  Those guys are typically running yagi's with 50+ watts pointed towards it.  Since I live in Tucson, I can hit it with 5 watts on a multiband vertical.  (I mean I litterally can see the repeaters up there from my house 30 miles away.)  I know that it reaches 120 miles north to Phoenix, at least 60 miles south to the Mexican border.  Not sure how far east/west.  But, it's doing a bang up job covering most all of southern AZ.
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RADIOPHONE

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Re: Opinions on 6M FM Repeater Wanted
« Reply #4 on: January 06, 2021, 08:43:19 PM »

I can't imagine anyone putting up another repeater.

The trend is mostly taking the existing ones down.
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WB8VLC

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Re: Opinions on 6M FM Repeater Wanted
« Reply #5 on: January 06, 2021, 08:48:27 PM »

My 6 meter remote base typically covers out to mobiles from 30 to 45 miles and this is with a 50 watt mobile on the other end in medium hilly forested terrain of northwest oregons willamette valley.

 To other repeaters and base stations my coverage is 50 to 90 miles depending on the others antennas.

A 5watt ht to my remote coverage is about 10 to 15 miles depending on ht antenna, commercial Moto or hammy crap.

My remote antenna is a hy-gain/nu-tronics v6-r, stacked 5/8wave that is only 65 feet above local terrain, my location terrain is about 500 feet msl whereas the average msl around me  for amobile varies from sea level to 1200 feet.

My remote base is a 60 watt motorola maxtrac connected to a 25watt uhf cdm1250 mobile.

The cdm1250 antenna is higher than the 6 meter but still 6 meter coverage is 10% to 15% improved over that of uhf.

In my urban rolling hills environment my 6 meter maxtracs effective sensitivity measured with an inline directional coupler in the 6 meter antenna feedline measures .615 uv while the effective sens with the 6 meter antenna replaced with a 50 ohm dummy load is .275uv indicating typical urban noise sensitivity degredation.

Still with this amount of local noise my 6 meter remote base still hears very well, base, repeater,mobiles and Ht's.

Since you are in a remote location  and at that height i would expect greater range and lower effective sensitivity close to .5uv or better.

You need a helper driving out to around 40 to 50miles with a 50 watt or greater radio and you with the powered 6 meter remote/repeater radio doing receiver measurements with the 6 meter radio powered up only.

Have you checked to see if your power supply is contributing some noise?

I have used the low band db201 before and it is a good antenna.

That MT LEMMON repeater is very low noise, during e season I use it easily from up here in oregon along with the 52.56  on Prescotts Mt Union and the Kingman 52.94 repeater from my remote base which is frequency agile.
« Last Edit: January 06, 2021, 08:56:56 PM by WB8VLC »
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W9IQ

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Re: Opinions on 6M FM Repeater Wanted
« Reply #6 on: January 07, 2021, 03:16:13 AM »

The 6 meter band has an 8.5 dB FSPL advantage over the 2 meter band. Given the differences in antenna system gain on both ends, receiver sensitivity, noise, etc.  I would say that you are well within the margin of error with your observations.

- Glenn W9IQ
« Last Edit: January 07, 2021, 03:21:31 AM by W9IQ »
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- Glenn W9IQ

God runs electromagnetics on Monday, Wednesday and Friday by the wave theory and the devil runs it on Tuesday, Thursday and Saturday by the Quantum theory.

N4DBM

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Re: Opinions on 6M FM Repeater Wanted
« Reply #7 on: January 07, 2021, 06:20:59 AM »

Thanks for the input..  As for the local noise, the power supply is definitely not the problem, and neither is anything else in the building itself.  There's a battery bank that powers everything in the building and throwing the main breaker doesn't make any difference in the observed noise floor.  There does seem to be a correlation between rainy weather and dry windy weather.  There's a three phase service entrance about 1000 feet away that is prone to generate noise on the transformer insulators.  I'll have to investigate that further.

I did some tests in the mobile yesterday.  Another repeater near the Raleigh area with about the same antenna and same height seemed to be performing as well as my remote base did, considering his stuff was working properly I suppose.

It's too early to tell whether the repeater venture will be worth the effort or not depending on who is interested in using it, if anyone.

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N2AYM

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Re: Opinions on 6M FM Repeater Wanted
« Reply #8 on: January 20, 2021, 12:42:08 PM »

This band when it is open is a great band even for FM simplex. It was probably about 20 years ago one early morning I was up running some errands listening to 52.525 and i was parked at a local store on the top of a small hill and the next thing I know I am listening to the typical southern drawl of hams in the south east chatting a lot so I called one and even with only a 10W mobile they heard me and we had great qsl activity between several hams in the south east.  When I moved and they had trouble hearing me they clued me in to some of there local 6m repeater pairs. so I QSY'ed to one and we had a long chat over about an hour - was a great time working them.
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WB5ITT

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Re: Opinions on 6M FM Repeater Wanted
« Reply #9 on: January 25, 2021, 02:31:01 PM »

Depends on several factors...2m rptrs and higher have gain antennas because of the size...to get 6db on 6m with DB212-x takes 4 dipoles...and a LOT of vertical real estate. I have been wanting to put one up on a 2000ft FM tower I have...but no elevator and I'll need a LOT of 1/2in Heliax min to get the separate RX at 1600ft and TX at 1200ft. I had a WACOM Lowband duplexer but never bothered to modify it to 6 and sold it when I needed the cash.
Also noise floor on 6 is worse than 2...Ive seen sites where the noise was 5uV or worse! A Noise Blanker is needed to help in those situations and most legacy gear uses a separate front end/AM wideband for the NB....so duplexer doesnt work with that. I prefer to use Midland or Kenwood LMR gear. The Midlands have a IF based NB and it works better than anything else I have used. Perhaps could work with a duplexer, never got to test. Mobiles of course will be running non gain antennas as well.....IF you can get a DB212-4 on XMT and RCV, or a -6 to make up for lost mobile gain, you will see much more range than a 2m rptr at the same height. I had a lowband (48MHz) base on a 400ft high DB212-3 (directional NW off the tower leg) and it could talk to and hear mobiles over 80miles away 24/7. Doubt a 2m rptr at that height with a DB224 in elliptical mode would cover the same (The lowband was using 7/8in Heliax too)
I have 53.15/52.15 coordinated on my FM site....may move it into the New Orleans area instead...

73
Chris
WB5ITT
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KB8VUL

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Re: Opinions on 6M FM Repeater Wanted
« Reply #10 on: April 03, 2021, 05:37:28 AM »

My noise floor at the site is over 1 uV.

So I am reading this right,,, that's 1.0uV not 0.1uV?
That right there is the problem for your range. 
I would for troubleshooting fire up Radio Mobile or another coverage mapping software and start looking in the areas you are falling out of the repeater for repeater talk in and see what the projected signal levels would be on talk in.  Like you said... The receiver is getting 20db Sinad at .275uV.  Your noise floor is 3 times that value. 
There is no 'fixing' that. 
You might throw a spectrum analyzer on the RX antenna and see how wide the floor is.  See if there is something there that seems like its a generated source.  If you can find it, and have the motivation to rework the antenna system to null it if it's coming from a specific direction, it might help.  But if you are seeing that just driving around at ground level.  I am thinking you might see if someone wants to swap you for a repeater of a different band to increase the performance.  Short of that, you can take the brute force path and get a 100 watt Maratrac mobile and just be able to overcome the noise floor from YOUR mobile for increased range.  But that is only going to increase YOUR range.
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