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#41
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Connecting multiple filters to multiband antenna
On Wednesday, March 18, 2015 at 1:32:51 PM UTC-4, Jeff wrote:
On 18/03/2015 13:54, Tom W3TDH wrote: On Wednesday, March 18, 2015 at 8:13:58 AM UTC-4, Jeff wrote: On 18/03/2015 10:49, Brian Morrison wrote: On Wed, 18 Mar 2015 06:44:55 -0400 Jerry Stuckle wrote: I would not expect matching a 50 ohm antenna to a good quality filter (which these are) would affect their response significantly enough to cause a problem. After all, this is the exact type of operation they are designed for. The stop band performance is dependent on the antenna and filter impedances out of band, at certain phases this can lead to a re-entering stop band. I've been dealing with the consequences of this in my day job very recently, it is a real and significant effect in some circumstances. It's also not trivial to fix. Indeed Brian, also if you look at the DCI filters there are quite large returns in the stop bands. Jeff What are the effects of this on my proposed operation? The effects are that it is not a good idea to parallel filters using coax and tee pieces. Jeff Jeff Are you deliberately trying to be obscure? "It's a bad idea" is not an effect but rather a rather vaguely stated opinion. Would you please advise what the deleterious effects of connecting the filters in that way would be. -- Tom Horne W3TDH |
#42
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Connecting multiple filters to multiband antenna
On 19/03/15 13:19, Tom W3TDH wrote:
On Wednesday, March 18, 2015 at 1:32:51 PM UTC-4, Jeff wrote: On 18/03/2015 13:54, Tom W3TDH wrote: On Wednesday, March 18, 2015 at 8:13:58 AM UTC-4, Jeff wrote: On 18/03/2015 10:49, Brian Morrison wrote: On Wed, 18 Mar 2015 06:44:55 -0400 Jerry Stuckle wrote: I would not expect matching a 50 ohm antenna to a good quality filter (which these are) would affect their response significantly enough to cause a problem. After all, this is the exact type of operation they are designed for. The stop band performance is dependent on the antenna and filter impedances out of band, at certain phases this can lead to a re-entering stop band. I've been dealing with the consequences of this in my day job very recently, it is a real and significant effect in some circumstances. It's also not trivial to fix. Indeed Brian, also if you look at the DCI filters there are quite large returns in the stop bands. Jeff What are the effects of this on my proposed operation? The effects are that it is not a good idea to parallel filters using coax and tee pieces. Jeff Jeff Are you deliberately trying to be obscure? "It's a bad idea" is not an effect but rather a rather vaguely stated opinion. Would you please advise what the deleterious effects of connecting the filters in that way would be. Give that duplexers are just filters connected, in some configurations, as T, I can't see an issue, provided you avoid introducing 'stubs' due to lead lengths. If you either keep leads short or go to the trouble of ensuring all avoiding critical lengths, you should be fine. To be blunt, I think there has been a lot of 'theoretical flag waving' in this thread. Having done much the same as what you wish to do and run the system for years without any noticeable issues, I've tried to give you the benefit of practical experience. I've three 'white stick' antennas up, plus a 2m and 4m dipole. I don't run 220MHz as we don't have an allocation there. Two of the white sticks are more or less vertically aligned and may be 15 to 20 feet apart. The third is 50 feet away, at the other end of the house. The 2m and 4m dipole are between the first two white sticks. Over the years the White sticks have been used for FM voice on 2m/70cm and one on 6m. Also things like packet, APRS, etc. Basically, whatever I'm experimenting / playing with at the time. The 2m dipole is dedicated to a local repeater, and one or more of the white sticks is usually on 2m and 70cm voice with various duplexers being used. I've even tested a 'crossband talk through' unit (repeater) for a local Raynet team here. I've only ever used typical amateur duplexers, simply as they were to hand. It seems you have some better units available. If you want to use the same antenna for a two radios on the same band, things do get more complicated, but you've not said you want to do that. I'd suggest you do some experiments and see how you get on, I'd be most surprised if you have any real issues. Perhaps mount the antenna on a ladder leaned against the house, as close as you can to the intended position. |
#43
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Connecting multiple filters to multiband antenna
On 3/19/2015 12:41 PM, Jeff wrote:
I have been keeping up with the thread, Jeff. And he was asking about using his diplexers. It was others who though adding filters would be helpful. I have never suggested this setup. You obviously have not, because this is what the OP asked: "Can I anticipate any ill affect from placing a coaxial Tee fitting across the output of one filter and connecting a jumper to the output of another filter in order to connect the transceivers to the multiband antenna? Would there be any additional concerns be raised if one of the two filters was the dual band model with separate connections for each of it's two bands on the end being used for input connections? What about if I make up the assembly using Three separate filters with Two of them connected to TEE fittings" That specifically asks about filters not diplexers. Jeff In this case the "filter" he is referring to is one section of the diplexer. Not necessarily the most technical description - but also not inaccurate. -- ================== Remove the "x" from my email address Jerry, AI0K ================== |
#44
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Connecting multiple filters to multiband antenna
On 3/19/2015 11:26 AM, Brian Reay wrote:
Give that duplexers are just filters connected, in some configurations, as T, I can't see an issue, provided you avoid introducing 'stubs' due to lead lengths. If you either keep leads short or go to the trouble of ensuring all avoiding critical lengths, you should be fine. I agree. It should work just fine. People do it all the time. This is really not that much different than what most repeaters use (except, of course, repeaters use very sharp filters and transmit and receive on the same band). To be blunt, I think there has been a lot of 'theoretical flag waving' in this thread. Having done much the same as what you wish to do and run the system for years without any noticeable issues, I've tried to give you the benefit of practical experience. I've three 'white stick' antennas up, plus a 2m and 4m dipole. I don't run 220MHz as we don't have an allocation there. Two of the white sticks are more or less vertically aligned and may be 15 to 20 feet apart. The third is 50 feet away, at the other end of the house. The 2m and 4m dipole are between the first two white sticks. snip You're right, Brian. A lot of flag waving with no basis in fact, by the usual suspects. -- ================== Remove the "x" from my email address Jerry, AI0K ================== |
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