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 Post subject: Re: Can you have more than one Radio on an antenna?
PostPosted: Nov Mon 27, 2017 5:36 pm 
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Joined: Feb Wed 25, 2009 4:06 pm
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Location: Morristown, N.J.
The answer is very simple: try it and see if it works.

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 Post subject: Re: Can you have more than one Radio on an antenna?
PostPosted: Nov Tue 28, 2017 1:18 am 
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Joined: Nov Wed 08, 2017 3:28 pm
Posts: 20
As a former CATV technician, I can say for a fact that a coaxle splitter, two way, has a 3.5 db loss and 7 for a four way. I'd didn't split the signal in half, but rather had the same loss no matter how strong or weak the signal was.

Jeff.


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 Post subject: Re: Can you have more than one Radio on an antenna?
PostPosted: Nov Tue 28, 2017 3:55 am 
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Joined: Sep Mon 18, 2017 2:23 am
Posts: 110
Location: Plymouth, MI
Now that I started all this trouble :oops: I will let you all know in the next week or so when I am set up how it works with two or more radios hooked up at once.
Thanks for all the input.


Dan


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 Post subject: Re: Can you have more than one Radio on an antenna?
PostPosted: Nov Tue 28, 2017 7:53 pm 
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Joined: Jan Mon 16, 2012 4:15 pm
Posts: 3614
Location: Near Brandon, Iowa
atwaterkent1 wrote:
Now that I started all this trouble :oops: I will let you all know in the next week or so when I am set up how it works with two or more radios hooked up at once.
Thanks for all the input.


Dan

It's really no trouble; opinions are like a-holes; everyone has one. But two radios won't be a real test. Your ears aren't going to notice a real reception rolloff until you have four (or more) sets connected in parallel.


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 Post subject: Re: Can you have more than one Radio on an antenna?
PostPosted: Nov Tue 28, 2017 8:07 pm 
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Location: Ashhurst, New Zealand
j8000 said:
Quote:
What if the Superhets are turned off, would that then no longer pose a problem to a radio on the same antenna that is on?


Nobody seemed to answer so I will....

You will still lose signal because the very first tuned circuit at the antenna input of the radio is still tuned - if it's tuned to a station that is a different frequency to the other radio, it will be a low impedance at all other frequencies and thereby 'suck out' all the signal - the reverse is also true, the other radio will 'suck out' your signal - it's a no-win situation for both of you.

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 Post subject: Re: Can you have more than one Radio on an antenna?
PostPosted: Nov Tue 28, 2017 8:16 pm 
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Location: Ashhurst, New Zealand
You can of course make your own splitter...

http://www.dxing.info/equipment/rolling ... bryant.pdf

Here's mine...

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 Post subject: Re: Can you have more than one Radio on an antenna?
PostPosted: Nov Tue 28, 2017 9:24 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 106
Location: E. Bridgewater MA USA
I have the rig that you asked about. My "shack" is 60 feet from my house, and I have a long-wire suspended between the two. I have boat anchor receivers in both locations.
Place a knife switch at each location. Get into the habit of turning "off" the antenna when you are through listening on whichever radio. As long as one knife switch is "open" it's like NOT having the second radio connected, because it isn't.
If you forget, and leave the switches both closed, you will notice a drop in receiver sensitivity, caused by the severe impedance mis- match created by the "load" of the second radio. Can't tell you how many times I have had to run back to the house to reset the antenna switch ! Took me a while, but now I remember.
One caveat, however. You might get into trouble with the AC circuitry in the two different locations. Hook everything up,close ONE knife switch and measure across the open one with an AC voltmeter. Anything above zero is cause for concern-employ an isolation transformer at one set.
Cheers,
Chuck
N1LNH


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 Post subject: Re: Can you have more than one Radio on an antenna?
PostPosted: Nov Tue 28, 2017 9:52 pm 
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Joined: Nov Sun 08, 2009 9:48 pm
Posts: 403
Location: Fredericton, Canada
As has already been mentioned the solution is a switch arrangement which routes the antenna to one radio input at a time. Here is a switch I made with an electrical junction box and a 5 pin rotary switch ( easily obtained on Ebay for next to nothing). Some coax cable plus connectors and you're all set.


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 Post subject: Re: Can you have more than one Radio on an antenna?
PostPosted: Nov Tue 28, 2017 11:02 pm 
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Location: Thornhill, Ontario
Leigh wrote:
... But transformers transform the load impedance back to the primary, factored by the impedance ratio. Given that the load impedance is a tube grid circuit, its impedance is multiple megohms.
- Leigh
True if the antenna primary a parallel tuned circuit, but not so if it's a series-tuned circuit designed, at the tuning point, to deliver "maximum nano-amps" to the RF primary coil, the other radio may then shunt signal. The fix is to just de-tune the other radio.
Cheers,
Roger

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 Post subject: Re: Can you have more than one Radio on an antenna?
PostPosted: Nov Wed 29, 2017 3:30 am 
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Joined: Sep Mon 18, 2017 2:23 am
Posts: 110
Location: Plymouth, MI
Since I started all this I thought I should report in. I finished setting up my antenna earlier today and, at the moment, have two AK model 40's sharing an antenna and ground. There was no noticeable difference in the performance or sound of either radio when hooked up one at a time or together, running or not.


Dan


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 Post subject: Re: Can you have more than one Radio on an antenna?
PostPosted: Nov Wed 29, 2017 5:08 am 
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Location: SoCal, 91387
^ That's not a good answer. What will the physicists on the board say now? :wink:

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 Post subject: Re: Can you have more than one Radio on an antenna?
PostPosted: Nov Wed 29, 2017 2:49 pm 
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Joined: Jan Mon 16, 2012 4:15 pm
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Location: Near Brandon, Iowa
fifties wrote:
^ That's not a good answer. What will the physicists on the board say now? :wink:

It's a perfectly good answer and was expected- at least, I expected it. The antenna loading that a radio presents is real but is also small... my prediction was that several radios (four, as I recall) would need to be hooked in parallel to a single antenna before a performance falloff could be perceived by the "naked ear".


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 Post subject: Re: Can you have more than one Radio on an antenna?
PostPosted: Nov Wed 29, 2017 3:18 pm 
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Location: Leo, IN or Zellwood, FL
fifties wrote:
^ That's not a good answer. What will the physicists on the board say now? :wink:


Not a Physicist but I do know how to operate Google Search. First a quote from some google page:

"Physics tells us that for every doubling of acoustical energy, there is a 3dB increase. Conversely, a 3dB decrease means the sound is cut in half. So, 3 is the magic number right? Well, not so fast. This is where we see a conflict between scientific calculations and perceived sound levels. “Perceived” sound levels report how our ears and brain interpret the sound. In other words, perception answers the question of “What sounds ‘twice as loud’?”

Perception
Sound studies tell us time and again that a 3dBA increase in sound level is barely noticeable to the human ear. In fact, you have to raise a sound level by 5dBA before most listeners report a noticeable or significant change. Further, it takes a 10dBA increase before the average listener hears “double the sound.” That’s a far cry from 3dB."

So yes the musically trained human ear is barely able to detect a 3 dB change in audio levels. That means that reducing the signal to your radio by 3dB is barely maybe able to be detected by the human ear. And 3 dB is a 50% reduction of signal level. In other words unless you put some type of meter on the output of the two radios you won't know the correct answer. Take it the easy way if you will. a 2 way splitter says on the little box 3.2 dB LOSS. That is 3 dB for the split and 0.2 dB for circuitry losses.

John k9uwa

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 Post subject: Re: Can you have more than one Radio on an antenna?
PostPosted: Nov Wed 29, 2017 3:20 pm 
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Joined: Jan Mon 28, 2013 9:35 pm
Posts: 820
Location: Santa Rosa, CA
The correct way to connect many radios to a single antenna is
via a critter called a 'multicoupler'. A common item in commercial
stations (HF and VHF). Its simply a box that has one amplifier stage
(low gain) that feeds a number of cathode or emitter followers,
one for each receivers. The idea is the frequency response is flat
over the intended range and with little or no gain but lots
of isolation between receivers and the antenna. Keeping
the noise figure down is very important.

If the discussion is about AM BC receivers, its probaby not
a big deal unless you are trying to use them for DX work.
However with SW and higher frequencies and multicoupler is
important for best performance. Do a 'net search for designs.
Steve


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 Post subject: Re: Can you have more than one Radio on an antenna?
PostPosted: Dec Sat 02, 2017 1:41 am 
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Posts: 5812
Location: Black Hills, SD 57745
Surprising how few here seem to have tried it themselves. Here's my method:

I brought out a short wire from the radios' antenna inputs to the front where it was handy. My long wire had an alligator clip.

If I wanted more than one radio on the same longwire (I had three wires up at the time to choose from) I added a .01 disc cap in series. I'm pretty sure using a cap in the antenna lead-in to isolate multiple receivers has come up on ARF before.

The fun part about having more than one radio going at once is trying Poorman's Diversity Reception. Of course, multiple antennas help with that, but you're just an alligator clip away to find out for yourself.

Here's one to ponder - would using a three-way wall switch and three-wire antenna run allow choosing which receiver on either end of the antenna is connected to the aerial while the other is not? I'd imagine a three-wire run would be needed, one of which would be the "hot" or actual aerial.

-Ed


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 Post subject: Re: Can you have more than one Radio on an antenna?
PostPosted: Dec Wed 06, 2017 2:15 am 
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Joined: Nov Thu 30, 2017 4:58 pm
Posts: 6
I just purchased and installed a multicoupler from Stridsberg in Louisiana. It's an active device that lets me hook up four AM radios at once to my long wire with no interference or need for switching. It's model number MCA104M and it's a bit pricey, around $200, but worth it for me.


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 Post subject: Re: Can you have more than one Radio on an antenna?
PostPosted: Dec Thu 07, 2017 5:04 am 
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For AM band work and some of the lower shortwave bands, a video distribution amplifier could be used to drive several radios from a single antenna. These amplifiers are unity gain circuits that provide isolation between the outputs and present each output port with a 75 ohm source impedance. Because these amplifiers were designed for 75 ohm environments, there might be a termination resistor on the input that needs to be changed or removed if the signal is coming from something that is high impedance, such as a longwire.


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 Post subject: Re: Can you have more than one Radio on an antenna?
PostPosted: Dec Tue 12, 2017 12:48 am 
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Location: Thornhill, Ontario
Alfredo_T wrote:
For AM band work and some of the lower shortwave bands, a video distribution amplifier could be used to drive several radios from a single antenna. These amplifiers are unity gain circuits that provide isolation between the outputs and present each output port with a 75 ohm source impedance...
An interesting idea! I've not done this, but one might match the antenna to the 75 ohms input with an aperiodic RF transformer, i.e. a step down single coil. You might even tune it, but then the antenna tuner would have to be tracked manually with the radio... not that difficult.
Has anyone tried this? I don't have a video amplifier, or I would try it.
Cheers,
Roger

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 Post subject: Re: Can you have more than one Radio on an antenna?
PostPosted: Dec Tue 12, 2017 5:59 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 106
Location: E. Bridgewater MA USA
I could be wrong (amazing) but I'm pretty sure that a video amp will NOT pass broadcast AM.
The scheme used in these amps is the basis for broadband RF amps that work on HF. Commonly used on ships and other situations where antenna space is non-existent. Made by Collins and others. Hard to find, and usually expensive.
Chuck
N1LNH


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 Post subject: Re: Can you have more than one Radio on an antenna?
PostPosted: Dec Tue 12, 2017 8:02 pm 
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Joined: Mar Mon 17, 2008 5:05 am
Posts: 5024
Location: Ashhurst, New Zealand
Quote:
There was no noticeable difference in the performance or sound of either radio when hooked up one at a time or together, running or not.


Insufficient info - were both radios tuned to the same frequency - if yes, then I would expect them to work well but did you have someone listening at one end while you twiddled at the other? Leave one radio connected and try listening to various stations at the other - any loss of signal then?

My HF multicoupler I bough on our auction site - I think it was NZ$50 say US$35 - Reaction Instruments 409-2 - probably ex gummint - 8 outputs VLF to HF - works well.

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