Here are a couple things that were less than obvious to me about the ARR 70CM switched preamp.
If you are going to power it with phantom power (i.e. up the feed line) you need to add a -C to the part number so they will add in the required choke from the feed line to the power input. But note that once you do this, you can't just use either phantom or external power. In my case, I got the choke ("I might need it someday") but used the external power. Oops...a nice short. It turns out that unless your transceiver has a high-pass filter (or just a cap!) you are probably going to be shorting out back through the feed line. When you do that, you may blow the choke and have to remove it anyway, depending on how much current got through it. (I'm not sure why they did not put a diode in, but hey...)
The other thing is that I was going to get one of their phantom power injectors also. The problem there is that they only work with receive-only. So unless you can find one elsewhere, phantom power may be useful mainly if you transceiver supplies it (sigh, mine does not).
And finally, another inobvious thing: The power connector has a third pin which, if you ground it, switches to transmit mode. So if you hook this up to the transciever, that's a way of getting around the "minimum power to switch" spec. (I think minimum power to switch is maybe 5W; my transceiver goes down to 5W, but with a 75' feed line, it's not gong to be 5W by the time it gets to the pre amp.
The SSB preamp (or at least the 2M one that I have) comes with the choke, diode, etc and has a lower minimum switching power. It is more expensive, though.
I hope this helps!
Burns, W2BFJ
Message: 6 Date: Tue, 7 Feb 2012 22:56:04 -0500 From: "Mike Ryan" mryan301@comcast.net To: amsat-bb@amsat.org Subject: [amsat-bb] Re: Receive Pre-Amps for 70cm Message-ID: 89830E8A0C73460A9F511377C4656703@MikeClone Content-Type: text/plain; format=flowed; charset="UTF-8"; reply-type=original
I second the comment about getting a switched one. Unless you have a dedicated RX or have disabled the TX, you will certainly pop a RX only amp. Its just a matter of when. Happened to me twice before admitting my clumsiness.
I've had very good luck with the ARR switched amps. I have two for 70 cm (one for the shack and one for my Arrow) and a 2M version as well. If the unit is to be in the attic, you can save some money by going for the inside 25 watt switched model (SP432VDG). Just don?t exceed the 25 watts. Also be aware that the FETs in these amps are sensitive, even on a switched model. Make sure your rig is completed powered off and your body grounded (to bleed off static electricity) before connecting or disconnecting antenna connectors. Its tempting to save a trip to the shack by leaving the rig on and do a quick swap, but don?t do it :(
Date: Mon, 6 Feb 2012 15:40:37 -0600 From: "Alan P. Biddle" APBIDDLE@UNITED.NET To: "'PETER SIMONSEN'" pureenduro@msn.com, amsat-bb@amsat.org Subject: [amsat-bb] Re: Receive Pre-Amps for 70cm Message-ID: 86B0819F8E944465B5B0C98010D7AAB7@WA4SCA Content-Type: text/plain; charset="us-ascii"
Peter,
A 70 cm preamp is always useful! There are a lot of them out there, but my experience is that ARR and SSB Electronics make the best. Definitely not the cheapest, though.
http://advancedreceiver.com/page2.html
http://www.ssbusa.com/gaasfet.html
Be certain to get one which is RF switched, and which will handle your rig's power. No matter how careful you are, you WILL transmit into it someday. Been there, done that.
You will need to split your single antenna jack on the rig to two lines. Almost any diplexer gives 50 db+ separation, but there are a few which are only 30 db or so. Worth checking.
73s,
Alan WA4SCA