Skipp. I will post a pic with the filtering specs later today. Its all here at my qth. Ian. Va2ir. Sent on the TELUS Mobility network with BlackBerry
-----Original Message----- From: "skipp025" <skipp...@yahoo.com> Date: Sun, 03 May 2009 03:50:00 To: <Repeater-Builder@yahoogroups.com> Subject: [Repeater-Builder] Re: desense question > va...@... wrote: > Running the hamtronics REP-200 with the optional 15 watt > PA in it. > After all the filtering, I get a whopping 8 watts out. Is the filtering you mention on the 15 watt PA board or is it external to the repeater chassis (on the outside of the box)? 8 watts is a very usable value for driving an external amplifier if you have the proper duplexer or antenna system in place. Lack of duplexer isolation and filtering will quickly come back as a problem generator. Many of the Hamtronics Receiver models are fairly hot front end wise. > I put a small strip amp inline with the TX port of the > repeater, before the filtering, and it caused desense. Maybe > tossing spurs - I have no way to test. If I understand what you're trying to describe, what you tried is probably not a good thing. > Location is also not great for the moment, and the > antenna is very temporary. A Diamond x500 connected with > COAX (please don't shoot me). The club antenna will be > down off the old tower (8 bay Sinclair) and I do have > the heliax for it. Nothing wrong with coax when you understand what occurs at UHF, which is most/much of the signal is lost (both transmit and receive) in long sections. Pretty much any non high quality and type coax is an unforgiving signal resistor (loss). Unless you're using a decent type double shielded coax... I would suspect most coax types also make a surprisingly good antenna (very leaky - both tx & rx directions). > The amp is a UHF PA off a mobile rig, and I needed about > 50 feet of RG58U to attenuate the signal from the repeater > into the amp module. Not good, probably better to bypass (not use) the 15 watt amplifier and drive the external amp direct from the exciter. I'm doing the same thing as part of the 224 MHz home brew repeater project I started describing in a post made earlier today. Pictures of in the group photos section. http://groups.yahoo.com/group/Repeater-Builder/photos/album/1157128983/pic/list > Is this my problem? Lack of shielding causing desense? > When I put everything back to normal, my test station was > solid copy. Hard to say without knowing more about your duplexer or cavity filter components. If you bump the Tx Power up, you must also ensure you have enough receiver protection in place. > What is my best option to get a little more oomph on the > output with out tossing megabucks at it? > Thanks > Ian > VA2IR The "budget minded" repeater owner/builder would probably put a mobile amplifier on the repeater. Better to not get greedy like many do and shoot your project in the foot. On your repeater I would expect 25 to 45 watts to be a very reasonable value. Keep in mind you'd better have a decent duplexer or antenna system in place or you'd better upgrade what you have. In many but not all cases a small blower (not a fan) moving air across the amplifier heat sink after modest tx talk time should be considered. Many repeater controllers have fan/blower control considerations built into their software and hardware logic. Many stuck up repeater builder types will tell you that using a mobile amplifier in a repeater application is a horrible idea. I can give you many examples and reasons where and why it's not the big sin many hard nose profess... but let's save that topic for another day. If you're properly dealing with the heat sink heat with proper air movement and/or duty cycle management, then by all means get on with other more important remaining issues. Sometimes you've got to work with what you have and when properly integrated into a system, you can use a mobile RF Amplifier in a repeater situation. cheers, s.
