[TenTec] Correction

[Keith Hamilton]

Thank you for your input and expertise Gary but I still don't see how the PBT setting would be correct for one filter (500 hz filter - PBT control at either 11 or 1 o'clock depending on the band) and not correct for the other filter (250 hz) unless the center frequency of the two filters is different.


On Jul 6, 2011, at 12:16 AM, CSM(r) Gary Huber wrote:

> Or you could just re-read closely the Ten-Tec owner's manual and note the 
> recommendation to move the PBT to either 11 or 1 o'clock depending upon the 
> band you are using and the sideband the CW is offset from the carrier 
> frequency.....
> 
> 
> 73 es DX,
> 
> Gary - AB9M (a 30 year veteran with TT radios)
> 
> -----Original Message----- 
> From: Ken Brown
> Sent: Tuesday, July 05, 2011 10:50 PM
> To: Discussion of Ten-Tec Equipment
> Subject: Re: [TenTec] Correction
> 
> Hi Keith,
> 
> There are three things which determine the audio frequency of the CW
> note you hear when listening to a CW signal with an Omni VI. Those three
> things are:
> 
> 1) The RF frequency of the signal you are listening to,
> 
> 2) The LO frequency that the Omni VI is generating,
> 
> 3) The BFO frequency that the Omni VI is generating.
> 
> The amplitude of the audio you hear is affected by many things. For this
> discussion the most relevant thing is where the bandpass of the 9 MHz
> filter is relative to where the LO has converted the incoming RF, AND
> the setting of the PBT which moves the signals passing through the 9 MHz
> IF around relative to the center of the 6.3 MHz filter in use.
> 
> When you have the PBT set for maximum "band noise" amplitude passing
> through both the 9 MHz IF filter and the 6.3 MHz IF filter, the the two
> IF bandpasses are as coincident as you can get them. The "center
> frequency" of this noise should be equal to the sidetone frequency that
> the Omni VI generates when you key it, and if you zero beat an incoming
> CW signal to your sidetone when you transmit your signal should be
> pretty near (in your case, being a piano tuner, damned near exactly)
> zero beat on the signal you have tuned in.
> 
> Assuming that the Omni VI LO system is working right there are two
> things you need to do to get the frequencies to work out right.
> 
> First you need to use the menu function that sets the sidetone
> frequency. This controls the offset of the LO system when you switch
> from receive to transmit, as well as controlling the frequency of the
> sidetone generated.
> 
> Second you need to have you BFO crystal oscillators operating at the
> correct frequencies. The are adjustable with trimmer capacitors.
> 
> You can always get the 6.3 MHz and 9 MHz IFs coincident by adjusting the
> PBT control, but when using a narrow 9 MHz filter you are stuck with the
> tone that passes through it. The best bet is to set your sidetone to
> match that.
> 
> You could misalign your BFO to get the tone you prefer, and then set the
> sidetone to match it, but if you do your frequency readout would be
> incorrect by the amount you have misaligned the BFO. The BFO changes
> frequency also between transmit and receive, so you would probably have
> to misalign both frequencies equally to keep the zero beat with the
> sidetone exact, and this would result in incorrect frequency display for
> transmit as well as receive. If you stay far enough from the band edges
> it would not be a problem.
> 
> I hope this helps,
> 
> Ken N6KB
> 
> 
> Keith Hamilton wrote:
>> I made a typo in my question. I meant to say I must tune the radio from 
>> 7.040.00 to 7.040.20 to center the 250 hz filter.
>> Sorry
>> Keith W8GX
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