[NLRS] Repeater amplifiers for SSB?

Thu Aug 4 19:43:23 EDT 2016

There are a couple ways around a class C final. One that was used by 
several stations including me in the Dallas area in the mid 60's was to 
run very narrow FM. With only first order modulation products it has 
both side bands and a carrier that looks like AM on a spectrum analyzer 
but the phase angle between the carrier and the modulation keeps there 
from there being any amplitude modulation. It is copied easy with a SSB 
receiver by zero beating the carrier and sounded better than the SSB 
from a 62S-1 transverter in those days. It was very simple to generate, 
I had built a CW crystal controlled (8 MHz range) tube rig with a 6360 
PA running about 18 watts. For NBFM, I built a starved high beta low 
current bipolar transistor amplifier with something like a 100K 
collector resistor and drove it with a dynamic microphone (or a crystal 
mike) and used the couple volts audio output to swing the voltage on a 
varactor diode on the crystal. The modern FM narrow band for commercial 
services is not a lot wider deviation so modern FM rigs will turn down 
to having only first order modulation products. Many that have backed 
off from the microphone as if on HF to prevent overdriving the radio 
(not a factor on FM) can be copied with the exalted carrier method using 
the SSB receiver. The limitation is that the modulation side band power 
is less than the carrier power and split into two sidebands and the SSB 
receiver hears only one. So its several DB down on received signal from 
a SSB signal of the same peak power. Another limitation is that hardly 
any one with a SSB receiver will realize they can copy it on SSB.

Another would be to add some gain so there's enough input for the PA to 
amplify the weak times of the SSB envelope and the modulate the envelope 
output power by varying the collector supply. There still can be 
intermod products caused by the class C PA when there are more than one 
tone in the SSB signal. Though I have alleged that voice audio signal 
can be broken down into half or whole single cycles of single frequency. 
I proposed that more than 40 years ago and got a university professor to 
read my engineering notebook and sign saying he understood what I 
claimed. I haven't yet tried to make hardware for it. Basically every 
half cycle of voice could be approximated at RF as a single frequency 
offset from the carrier frequency for the time period of that half 
cycle. So it would require a very agile synthesizer not even a dream in 
those days.

73, Jerry, K0CQ

On 8/4/2016 6:02 PM, Dr. Gerald N. Johnson wrote:
>
>
>
>
> On 8/4/2016 5:35 PM, Doug Reed wrote:
>>
>>
>> My opinion is that you could probably linearize an old vacuum tube FM
>> amplifier much easier than you could a transistor amp. Although
>> finding one of the old GE MASTR Pro 330W amps that used a 4CX250 might
>> be a little hard these days.... With the old Class C transistor FM
>> amps having multiple parallel finals, I wouldn't even want to attempt
>> biasing them.... Go with something modern instead.
>>
>> Motorola often went in for odd-ball conduction-cooled power tubes.
>> They usually had beryllium for the heat sink insulator so they were
>> treated as hazardous waste. I can get you one of those up in Little
>> Falls, MN if you want to pick it up..... It is still in a Motorola
>> Motrac vintage FM repeater in a 6 foot rack.... Probably no more than
>> 150W RF out. :-)
>
> Actually its beryllia, beryllium oxide ceramic. A better heat conductor
> than solid aluminum Also often used in RF power transistor cases.
> Contact or ingestion of beryllium or compounds has been proven to cause
> cancer. So long as its not powdered and stays solid it appears to be
> safe. Many RF power transistor data sheets include warnings about
> cracking the beryllia.
>
> 73, Jerry, K0CQ
>>
>> 73, Doug Reed, N0NAS.
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