Hi Doug / Paul / Nick / Patrick.
Thanks for all the comments and ideas. It seems the diplexer may work but only if it can filter the 70cm transmit output, not for desense, but for spurious emissions coming out of the IC706.
A quick check earlier today following Patrick's reply shows there is significant wideband noise transmitted on 2m whenever the 706 enters its transmit mode on 70cms. This seems to be a 'feature' Moving the antennas apart by 30 feet reduces the noise to the general background level. Unfortunately a 30 ft boom isn't a practical solution.
I've tried a cavity filter in the 435MHz transmit chain and miraculously the noise on 2m disappeared. But again, a cavity is not the easiest thing to include. I'll have a look at the diplexers. Hopefully there will be one with a low loss, but now I know the 706 is the problem I may just add a high pass filter in line with the output on 435MHz.
Hopefully, after monitoring telemetry for the last 11 months I'll get this up and running over the weekend and finally manage a QSO on AO-73
Fingers crossed.
Thanks for all the great suggestions
David
Here's the AMSAT link about "Desense" that describes the method to try.
http://ww2.amsat.org/?page_id=2136
GL
Nick, KB1RVT
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-----Original Message----- From: Doug - k4gkj [email protected] To: n8hm [email protected]; g0mrf [email protected] CC: amsat-bb [email protected] Sent: Fri, 31 Oct 2014 21:10 Subject: Re: [amsat-bb] ICOM 706G phase noise
My 706mk2g doesn't do this. And at the moment, I have a diplexer on my tower to have one feedline share VHF & UHF antennas... I am not happy with the 2.5db+ of loss that comes along with putting that diplexer on... Doug K4GKJ
Doug Bennight K4GKJ 850-528-5772 850-926-2052
-------- Original message -------- From: Paul Stoetzer [email protected] Date: To: David G0MRF [email protected] Cc: [email protected] Subject: Re: [amsat-bb] ICOM 706G phase noise
David,
Try a diplexer on either the transmit or receive side (whichever works better) with the common port to the antenna, the appropriate band port hooked to the radio, and the other band port left disconnected. If your Icom is putting something out on 2m when transmitting on 70cm, that should filter it out.
73,
Paul, N8HM
On Fri, Oct 31, 2014 at 12:41 PM, David G0MRF [email protected] wrote:
Hi all.
Inspired by the FUN on the YouTube videos from the car park at Baltimore, I've been trying to set up a satellite station using two independent radios. An IC706G on 70cm transmit and an FT736R on 2m receive. Antennas are a 4 ele yagi ( horizontal ) on 2m receive with an AMSAT-UK filtered preamp. Transmit antenna is a 9 ele Tonna mounted vertically. Antennas are on a rotator using a fibreglass boom about 1.8m long.
The problem: Whenever I press the 70cm transmit 'button' - ptt on SSB, or key on CW I get S8 noise on the 2m receiver. (and S6 without the preamp)
Note...This does not appear to be RF overload as I can turn the power down to minimum on SSB, even remove the microphone and the noise level remains. On CW the noise level is constant when the 706 is in transmit mode. It does not appear and disappear with each dot or dash.
My conclusion is that on 70cm the IC706G is transmitting something on 2m whenever it is in it's transmit mode.- possibly phase noise.
Has anyone else come across this issue with ICOMs or is it just this one? and is there a known minimalist solution.
Many thanks
David G0MRF
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_______________________________________________ Sent via [email protected]. AMSAT-NA makes this open forum available to all interested persons worldwide without requiring membership. Opinions expressed are solely those of the author, and do not reflect the official views of AMSAT-NA. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb