[amsat-bb] Re: Arrow 10W Duplexer Performance Measurements

Allan Saul allan at rfdesign.co.za
Wed Oct 21 11:32:38 PDT 2009

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.


-----Original Message-----
From: Bruce Robertson [mailto:ve9qrp at gmail.com] 
Sent: 21 October 2009 02:01 PM
To: Allan Saul
Cc: amsat-bb at 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'

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

On Wed, Oct 21, 2009 at 8:21 AM, Allan Saul <allan at 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:\SoftPage_V5\files\5645456\Download-Library\Amateur-Radio\ZS1LS\Mode-J-Filter
> 73's
> Allan ZS1LS
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