I've always wanted to build a preamp that incorporated some helical filters (resonators), just haven't gotten around to it. It should be possible to build a small one to do just what you want.
73, Joe kk0sd
-----Original Message----- From: amsat-bb-bounces@amsat.org [mailto:amsat-bb-bounces@amsat.org] On Behalf Of Bruce Robertson Sent: Wednesday, October 21, 2009 2:52 PM To: Allan Saul Cc: amsat-bb@amsat.org Subject: [amsat-bb] Re: Arrow 10W Duplexer Performance Measurements
Good point, Allan. Actually, I was especially thinking of doing this in some sort of arrangement that avoided the duplexer, perhaps using an FT-817 on FO-29.
Even with the duplexer, there might be some solutions to the problem you present. For instance, one could try making some sort of vox-enabled power switching for the preamp, which turned it off when one began to transmit. Then you'd at least have the benefit of the preamp when you were copying the other station(s).
73, Bruce VE9QRP
On Wed, Oct 21, 2009 at 3:32 PM, Allan Saul allan@rfdesign.co.za wrote:
Hi Bruce,
I am afraid you are very much mistaken in your logic here. For mode J on AO51 say, The 5W signal you transmit on 2m will completely drive that 70cm preamp between the antenna and duplexer into saturation unless you put a very good filter on the input (the desense issue). That insertion loss might negate any gains you make on the preamp, increase your noise floor by 20dB and add a lot of hassle, and more importantly weight.
Actually, the 1.2dB insertion loss is better than I was expecting and good enough for the short cable run to the HT. It is what it is and its good enough for the job it was intended for.
73's Allan
-----Original Message----- From: Bruce Robertson [mailto:ve9qrp@gmail.com] Sent: 21 October 2009 02:01 PM To: Allan Saul Cc: amsat-bb@amsat.org Subject: Re: [amsat-bb] Arrow 10W Duplexer Performance Measurements
I'm grateful to everyone who has contributed to this discussion.
It strikes me that the greatest improvement we could make to hand-held yagis would be to somehow integrate a low noise preamp circuit very close to the 70cm port. I have an indoor-style ARR preamp that I've thought of connecting to the boom with cable ties. A powersupply using AA batteries and a DC to DC buck-boost chip from, e.g., Maxim, would keep the whole thing light. (Alternatively, I see that the max voltage for my ARR is pretty high: I might get away with a pair of Nicad '9v' batteries.)
Like so much of amateur radio, it's more of a challenge of construction than anything else.
Has anyone experimented with this sort of improvement?
73, VE9QRP Bruce
On Wed, Oct 21, 2009 at 8:21 AM, Allan Saul allan@rfdesign.co.za wrote:
Quite a lot of guys are using the handy Arrow Model 10W duplexer for the handheld 146/437 antenna and mine arrived here today so I thought I would put it on the network analyser and see how it performs.....
From the Radio cable to the 2m antenna connector an Insertion Loss of
0.75dB was measured with a rejection of 57dB at 70cm. The VSWR at 2m was 1.24:1
From the Radio cable to the 70cm antenna connector an Insertion Loss of
1.2dB was measured with an attenuation of 56dB on the 2m signal. The VSWR at 70cm was 1.29:1
The VSWR on the 2m port was 1.21:1 and on the 70cm port was 1.20:1
For those guys wanting to look at the actual plots they can be found here
http://www.rfdesign.co.za/default.asp?pageID=785423593&filePath=D:%5CSof... V5\files\5645456\Download-Library\Amateur-Radio\ZS1LS\Mode-J-Filter
73's Allan ZS1LS
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