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Re: Plagued with Mode J "noise" on TX



Hello This is Yoshi.

  Do you have just only one duplexer?

  I do not well about the charactor of the front-end of FT-100, but
when I used my FT-817 for 435MHz downlink receiver, Its sensivity
was brocked with 145MHz transmittion. But in the case of using KENWOOD
TM-441 for receiving (for FM birds), It had not.
  My uplink power is just 10W so I used my duplexter for just only
UHF receiver. Then It had become working well. If you have one more,
lets put it in the line of receiver. Or please try to use your duplexer
in the line of receiver only.

  And, how about to use some sort of receiving antenna only for 70cm?
You are now using 2/440 dualband whip so your uplink power will reach
to the front of your receiver with not so much loss.

  73 de Yoshi JF6BCC.

At 2001/01/24 05:48:35 Scott Townley wrote:
> I know this is an old subject, but I can't seem to shake it...
> I'm setting up a Mode JA mobile station, and when I TX on 2m (160W
> RFConcepts brick to a 5/8wl whip) the "crud" on 435MHz RX (FT-100 using
> dual-band 2m/440 whip) is horrendous.
> Had the same problem in the "home" station using yagis, but never chased it
> too seriously because I knew I'd be moving Mode J out to the truck.
> 
> I can do 145x3=435 so, since I don't have a 2m BPF on hand, I used (at
> someone's suggestion) a 2m/440 duplexer (Comet CF-4160).  To be sure I
> measured the LP/HP response of the duplexer on my network analyzer (doesn't
> everyone have one?), and it was:
> 	VHF port (LPF)	-3dB thru loss at 215 MHz
> 				-49dB thru loss at 435 MHz
> 	UHF port (HPF)	-3dB thru loss at 264 MHz
> 				>-60dB thru loss at 145 MHz
> 
> Not a bad device!  So any transmitted third harmonic from my uplink should
> be 60dB rejected, plus path loss and antenna mismatch.  But it STILL cruds
> up the receiver so bad I can't hear my downlink!
> 
> What am I missing?  TX is known good (both on RS-12 and on service
> monitor).  Duplexer was placed right at radio and unused UHF port was
> terminated.  
> 
> Thanks!!
snip!


Yoshihiro Imaishi JF6BCC/KH2GR
mailto:jf6bcc@jarl.com
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