On Thursday, March 12, 2015 at 11:41:23 PM UTC-4, Fred McKenzie wrote:
In article ,
"Ralph Mowery" wrote:

"Tom W3TDH" wrote in message
...
I am going to declare myself lost on this one so please be patient. I had
though I had addressed these issues when I said I was using a DCI Dual
Band Filter and Diplexer. Is the DCI combination filter and diplexer
insufficient to protect the two radios from each other? DCI claimed it
would be. The model number is DCI-146-444-DX-DB. The web sight were it
is listed is
http://www.dci.ca/?Section=Products&SubSection=Amateur. If I need to add
Duplexers it is practical to do because the mobile ones available used are
manageable money. If there is a real chance for damage in the event ..of
simultaneous transmission then I will need to add circulators and dummy
loads to the output of both radios. That will end up being a little
pricy.


That DCI should be plenty to protect the two rigs. You may have a desense
on the 440 receiver if it on a near 3 rd harmonic of the 144 transmiter.. It
won't be enough to cause any damage, just enough to block the 440 receiver.

I agree that you are not likely to damage a radio. The common duplexer
(or triplexer) is often used to connect a single multi-band antenna to
multiple connectors of a multi-band radio, which is essentially multiple
radios in a single package. The difference between this and what you
are planning, is that the multi-band radio is usually not used for
simultaneous reception and transmission. Or at least you would accept
some desensitization if it occurred.

You can choose frequencies such that the third harmonic of the Two Meter
frequency is not in the IF passband of the 440 receiver, but you are
likely have overloading of the receiver's broad front end. (You may
also have some overloading of the Two Meter radio due to the amount of
power involved.)

That said, go ahead and try it. It may work well enough to meet your
needs. If it does not work out, the alternative is a "real" repeater.

One advantage of a repeater, is that local users can hear each other.
With your Hot Spot, local users are talking simplex.

73,
Fred
K4DII

Fred

As I already said I am not totally conversant with D-STAR. I was under the impression that the persons participating in any given QSO could hear each other over the access point they were using. I had pictured it as somewhat akin to the remote receivers on our club's analog FM repeater in that the other users on the QSO would hear the conversation over the repeaters output. Our D-STAR repeater is located in Germantown and I do not actually know what it's effective range is. We operate six different sites with four repeaters, four remote receivers with radio links back to the analog two meter repeater, and two APRS digipeaters. In addition to those sites we will have several members hosting D-STAR hot spots in order to fill in the edges of our service area that are outside the effective receive range of portable radios. Those using mobile or base station radio will, hopefully, be able to raise the repeater without resorting to one of the hot spots We can make changes to the location of the various elements of our repeater system including the location of the D-STAR repeater itself if that is needed to allow all users to hear the conversation.

On the harmonic de-sensing issue I can purchase a DCI low pass filter that cuts off at 160MHz if that becomes a problem. It would be inserted between the two meter radio and the filter/diplexer so that the harmonic would not reach the diplexer at all. Part of this question affects operations well beyond my home location. The county ARES unit is gearing up to support hospital emergency communications in our area. Our first client hospital purchased an Icom IC-7100 transceiver for the hospital station. If that remains the only transmitter at the hospital's EOC then the use of directly connected multi band antennas will work fine. But if the hospital discovers that it needs more than one mode or frequency to be used at the same time then our team will have to devise a Diplexing setup in order to keep the two radios from clobbering each other. I could see them needing both local tactical voice and medium range digital at the same time in a real disaster situation.

In the Mid Atlantic region the most common natural disaster with region wide effects are severe ice storms. Since I moved to three land in 1980 we have had three such storms that have wiped out communications infrastructure over wide portions of our region. It usually takes at least a week to get all of the wires and fibers back up in the air. Were about fifteen years out from our last bad one so we're about due. The hospitals have learned that continuing to operate when it is very difficult to talk to anyone that is not on campus is more than challenging. That's why I think they are going to want more than one communications pathway available to them and nothing carries long documents as quickly and accurately as digital.

Thanks again for taking the time to help on this.

--
Tom Horne W3TDH