[Milsurplus] Tubes?

[John Vendely]

Hi Mike,

The "pulse sweep generator" was a simple transmit frequency acquisition 
aid.  This series of radios had a very simple transmitter consisting of 
a frequency modulated electron-coupled "power" oscillator coupled 
directly to the antenna.  The radio featured an AFC system to lock the 
transmitter frequency to that of the receiver by feeding a DC control 
voltage derived from the receiver's discriminator back to the transmit 
oscillator, thus holding it on frequency (the receiver remained on while 
transmitting).  But sometimes, the transmitter was initially far enough 
off frequency that it fell outside the receiver's IF passband, and no 
AFC voltage would be developed.  The transmitter would then simply drift 
around off frequency.  When this occurred, the sweep generator was 
designed to automatically activate, sweeping the transmit frequency back 
and forth.  The frequency sweep was made wide enough to ensure that at 
some point, the transmitter would enter the receiver IF passband, and 
the AFC could then lock.

The original PRC-8, 9, and 10 radios did not have the sweep frequency 
acquisition feature, and evidently experienced problems if 
transmit/receive frequency tracking wasn't pretty close.  In the "A" 
model of the radios, they sacrificed one IF amplifier, replacing it with 
the sweep oscillator.

73,

John K9WT

On 4/19/2012 1:08 PM, Michael A. Bittner wrote:
> OK, Thanks for the info.  But, why would you need a pulse sweep generator in an FM transceiver?  Mike, W6MAB
>    ----- Original Message -----
>    From: David Ross
>    To: milsurplus at mailman.qth.net
>    Sent: Thursday, April 19, 2012 9:34 AM
>    Subject: Re: [Milsurplus] Tubes?
>
>
>
>
>    On 4/19/2012 7:18 AM, Michael A. Bittner wrote:
>    >  What were these replaceable circuit modules use in, especially the pulse sweep generator??  Mike, W6MAB
>    >  http://www.ebay.com/itm/ASSORTED-SPECIALTY-TUBES-TUBE-CADDY-6-/330719816641?pt=LH_DefaultDomain_0&hash=item4d006febc1
>    They are used in either PRC-8s&  PRC-9s&  PRC-10s, or PRC-8As&  PRC-9As
>    &  PRC-10As.  There are about ten different types of these modules, some
>    have miniature tubes inside and some are passive.
>
>    The six of them should ship for just a couple of dollars...
>
>    73
>    Dave Ross    N7EPI
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