[amsat-bb] Re: Downlink issue with Icom IC-910H

[Ronald Nutter]

Jeff/Bruce:

Thanks to both of you for your reply.  I put things together kinda quick 
today, so I skipped the one little step about putting the filter in.  I 
am using UHF side of a Comet CF-160 Duplexer.  At some point I might 
change to a "dedicated" filter but since I have been recently laid off, 
that expense will need to wait a while.

Thanks,
Ron

Jeff Mock wrote:
> 
> 
> Ronald Nutter wrote:
>> After not having used my IC-910H for a while due to moving across 
>> country, I unpacked it tonight and setup my antennas.  I was able to 
>> make contacts on SO-50 and AO-51 with one small problem.  I can hear 
>> signals on the downlink but not mine.  When I transmitted, all I could 
>> hear was some white noise when I was transmitting.  I head several 
>> exchanges but it was like I was in half duplex.  This was a working 
>> system before the move.
>>
>> I have good quality coax running from the IC-910H to an ICOM preamp 
>> for each side (VHF or UHF) and then running to the antennas.  I 
>> believe that I have used all of the original coax but I could be 
>> wrong.  The only thing I havent put in place was my mode J filter on 
>> the UHF downlink. Could this be causing my problem with not hearing my 
>> signal on the downlink but hearing those who are calling me ?  Sorry 
>> for what is probably a stupid question but I am getting all the kinks 
>> worked out in my setup before Field Day.
>>
> 
> I think the lack of a filter on the 70cm downlink might be the problem. 
>  I started out without any filter on the 70cm downlink, I added a DCI 
> 70cm bandpass filter because of local QRM from commercial radios and it 
> also improved my ability to hear the downlink on my 910H.  As you 
> suspect, the 2m transmit might be desensing the 70cm receiver or preamp.
> 
> I tested this by listening to a weak faraway 70cm repeater while 
> transmitting on a clear portion of the 2m band.  You can do this with 
> and without the 70cm preamp and hear if the receiver is desensing. I 
> found that the filter made my troubles go away.
> 
> jeff
> AD6EO
> 
>