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Author Topic: Operating Multiple Radios At One Location  (Read 9045 times)
AK4SK
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Posts: 150




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« on: January 01, 2014, 06:54:01 PM »

There are three main scenarios I can think of where I would want to operate multiple radios simultaneously from my QTH.

1. Having a dedicated RMS relay station while also having a second HF station for voice, etc.

2. Having a dedicated VHF APRS digipeater/igate while also having a second VHF/UHF station.

3. Having a QRP WSPR station running while also having a second HF station for voice, etc.

My first question is, can I use the same antenna for both stations in any of these three scenarios? If so, how? By using a duplexer? If two dedicated antennas are required, how do I keep one station from interfering with the other?

I know there are many hams that do one or more of the scenarios listed, I'm just not sure how.

Thanks,
Chris
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KQ6Q
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Posts: 991




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« Reply #1 on: January 01, 2014, 09:46:55 PM »

It would be expensive and difficult to use two radios on one antenna in any of these scenarios. You will keep to keep the antennas separated as much as possible, and in each other's pattern null (like for the VHF digipeater and the general use VHF/UHF FM station vertical antennas offset to the same side on a common mast).
for the HF combination, you won't get must distance separation, but have one antenna vertical (RMS relay) while the primary antennas are horizontal - or the other way around, if a dipole would work for RMS and you use a trap vertical for general use.
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AK4SK
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Posts: 150




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« Reply #2 on: January 02, 2014, 08:27:11 AM »

Thanks, I wondered about that. It is pretty easy for me to put up multiple VHF antenna but a vertical HF antenna would be difficult due to the lack of space for a radial system.

Other than antenna spacing and geometry nothing is required to keep one transmitter from overloading the other?

73
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KJ7WC
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Posts: 69




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« Reply #3 on: January 03, 2014, 05:57:36 PM »

If antenna separation is insufficient to prevent receiver desensitization, then additional filtering is needed; it's that simple.

A friend and I operated a single BuddyPole with a 15m dipole and 20m ground-plane. We used two separate rigs to feed each of the two antennas. As you can imagine, attenuation between the two antennas was limited to orientation only, since the two antennas literally crossed at the center. It was quite a spiritual sight to behold.

I started to detail a few scenarios here, but it's probably best to leave those as response to any specific questions you have.
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KQ6Q
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« Reply #4 on: January 04, 2014, 02:12:36 PM »

More multiple HF rigs, if they operate on different bands, you can your a bandpass filter between each rig and its antenna to keep it from seeing the radiation from the other rig and antenna. We do this for multi-transmitter field day sites.
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AK4SK
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Posts: 150




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« Reply #5 on: January 06, 2014, 08:26:01 AM »

Thanks again. At this point I'm just trying to get some ideas for the time when I actually want to run multiple stations. On HF band pass filters may just be the ticket as an RMS Express station will probably only be on one to two bands.

73,
Chris
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KJ7WC
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Posts: 69




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« Reply #6 on: January 07, 2014, 07:08:01 PM »

If you're only going to have two HF radios sharing a single antenna, you can probably get away with a properly designed high- and low-pass filter pair. For a third radio, Dunestar makes a pretty spiffy set of triplexer and bandpass filters: http://www.dunestar.com/store/HF-Triplexer-BandPass-Filter-Package-pid-7.html.

Anyway, that should give you an idea of the direction you're heading.
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AK4SK
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« Reply #7 on: January 08, 2014, 09:03:35 AM »

Thanks, I'll take a look at those.
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HURRICAINE
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« Reply #8 on: January 11, 2014, 10:54:50 AM »

There was an article a while back in QST magazine about a group that was using a beam antenna on two frequencies at the same time on HF.  It incorporated some type of deep cavity filters.

I looked into cavity filters, which is what should be used at any field day site with multiple receivers.  They were very expensive!

The bottom line is - the reason why the big guns gets such high scores is because they use these filters and they do not experience the desense that others does without them.
Probably the reason why most people brings their worst transceiver to field days and not their best.

Most people do not know how to string up antenna's, and they put them too close together.

Some people cheats and puts up towers that they use every year and has trailers that they use to sit in while they operate, yet they claim that they are not - for Field Days.
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KB1NXE
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« Reply #9 on: January 12, 2014, 04:12:45 PM »

I guess you could make cavity filters out of some form of mining pipe as they'd be enormous.  Heck, the one's for two meters are about 4" in diameter and a meter long.  The size is frequency dependent.  I just wonder if building them in the ground to save space would also detune them and which way...

So, for 10 meters, the cavity would be a meter in diameter and 5 meters long.  I'd hate to see them for say - 40 meters!

To the OP, do some research into Bandpass filters.  It's what I use here on two HF radios.
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KD8MJR
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« Reply #10 on: January 13, 2014, 08:43:16 AM »

Wow that big for 10m?
What is the formula for the size vs frequency?
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KJ7WC
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Posts: 69




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« Reply #11 on: January 15, 2014, 11:44:00 PM »

... I looked into cavity filters, which is what should be used at any field day site with multiple receivers.  They were very expensive! ...

What leads you to that belief? The only reason that you'd need to use cavities is use the same antenna for two radios on the same band, but that would greatly limit the available bandwidth for each radio. If your club is into sharing antennas that much, it should maintain adequate separation between CW and voice stations. Each radio sharing an antenna would then need its own bandpass filter with a much more reasonable Q. All the bandpass filters should then share a properly rated multiplexer.
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W2RWJ
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Posts: 198




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« Reply #12 on: January 24, 2014, 06:28:42 PM »

If you're only going to have two HF radios sharing a single antenna, you can probably get away with a properly designed high- and low-pass filter pair. For a third radio, Dunestar makes a pretty spiffy set of triplexer and bandpass filters: http://www.dunestar.com/store/HF-Triplexer-BandPass-Filter-Package-pid-7.html.

We have the Dunestar HF Triplexer PLUS mounted on a rack panel at N2MO.  We used it last year on field day into a beam with good results.  I would caution that you need to keep an eye on the power as they are only rated at 200W ICAS

Ranko, 4O3A, makes a filter / triplexer set that is legal limit.  http://www.4o3a.com/index.php?option=com_content&view=article&id=91:hf-high-power-band-pass-filter-series-s&catid=93&Itemid=493/ 

73 Martin Flynn
W2RWJ


  
« Last Edit: January 24, 2014, 06:30:54 PM by W2RWJ » Logged
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