[Elecraft] Digital modes on 144MHz only

[Mike Harris]

Our first commercial 11 metre dish earth station built in 1984 had a 
4GHz 60dB gain, 33 Kelvin, electrically cooled two stage parametric LNA 
at the feed horn. the cable to the receive system was LDF4-50 with 20dB 
loss to a six port passive splitter.

The LNAs despite being pressurised constantly with dry air with a small 
bleed hole had to be purged of frost every six months by turning the 
cooling into heating and increasing the outflow of air. After 12 hours 
of cool down they had to be retuned, pump frequency and power to achieve 
60dB flat gain over 500MHz bandwidth. Times have changed.

Regards,

Mike VP8NO

On 05/07/2019 10:08, Wes wrote:
> That isn't quite right either.  The preamp gain must be much higher than 
> the following losses to minimize second stage degradation. (Line loss 
> degrades the NF of the second stage)
> 
> Wes  N7WS
> 
> On 7/5/2019 5:35 AM, Martin wrote:
>>
>> That's not quite right. The overall system noise is determined by the 
>> preamp noise figure when mounted as close  to the antenna as possible. 
>> Cable losses (=noise) after the preamp can be neglected, as long as 
>> the gain of the preamp is higher than the losses in subsequent 
>> components. So the cable AFTER the preamp can be pretty lossy. OTOH, 
>> too much gain from the preamp easily overdrives your transceiver's RX. 
>> A good balance between gain vs. cable losses is mandatory. The noise 
>> figure of the pramp is crucial.
>> If you are satisfied with your transverter's noise figure , mount it 
>> close to the antenna via a short run low loss cable, if you can. This 
>> saves the expenses for a preamp.
>>
>> This applies to the RX path. I'm not talking cable quality or output 
>> power for TX.