My 23cm dish plus transverter is now down for revision
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| measured by ham 0.15 db NF! it has a band filter |
The new SKY67151 LNA just fits in next to the relayreplacing the SPF5189z
these Chinese eBay connectors can not be used for 23cm 1300MHz
it will result in high SWR and lower output and possible instability
My transverter is a modified DB6NT + 30W PA
And SPF5189z preamp 0.73db nf this worked very well
F.i. in oktober test OM3KII was worked 916km in mostly flat propagation!
But some issues self oscillating reduced total gain bad TX matching, interfering 900MHz 4G
Cooling is insufficient for long tx-ing it needs an external heat sink.
I was thinking of modifying the SPF inserting a band OFW filter as described
in FUNK FA10-18 953 DL2EWN , then in the same article the SKY69151 was noted having such a filter and very low noise.
I want to replace the SPF5189Z with the new SKY 23cm preamp VHF design nf : < 0.3 dB
The XVTR is controlled over a 30m rg48 at 146-148 MHz i.f. and a control cable 8 pole CAT
down in the shack 146MHz loss -6dB over 30m RG48 so i need some extra overall gain to compensate this.
Another struggle was to get a good connection from the DOWKEY SMA relay to the N -connector at the back of the dish. No cable loss
But loss in the used SMA adapting to N
I inserted a small coax SWR d-coupler type LA8AK in the RG58 connection between the PA and antenna relay to monitor POWER and reflection or SWR 2x 20mm pickup wires. c.a. 2.5V /30W
The SWR was high and unstable mostly high even with a dummy load connected.
Specially in damp weather the SWR went up high but at inspection no water was leaking in.
I suspected bad connection and or the SWR bridge it self
Receiving and signal looked okay ?
Once the system is in the mast everything that can go wrong will go wrong that is Murphy law.
for a thorough inspection at the workbench , plenty of time now.
After several tests i found that the inserted LA8AK SWR bridge works just fine
but the connectors between relay and feeder caused high SWR.
The SMA relay is connected direct to the dish feeder coaxial tube with N-connector
This feeder tube is lead back through the dish into the XVTR box
It needs some adapter SMA to N male and SMA extension piece to get clear from the middle pole of the small 403-130 Dowkey relay with its 3 SMA close to each other.
These SMA adapters screwed up the SWR complete!
the LA8AK hi-SWR measured right.
So watch out the Ebay Chinese SMA most of them will not work at 23cm
Not using PTFE isolation . A pity since they are easy and cheap to buy.
I am willing to pay extra for SHF qualified connectors
Must replace SMA / N for SHF qualified connectors.
The new SKY67151 LNA for 23cm sets a benchmark in low noise preamps
Very well build with band pass filter to keep the strong 4G and other signals out
I have increasing noise bursts in several directions caused by strong 900MHz signals nearby
So i hope to get a clean 23cm reception with even more sensitivity.
The gain of the double cascade SKY67151 is 36dB ! no self oscillation
Al my other preamps for 23cm suffered self oscillating more or less.
Even the well designed SPF5189z PCB sometimes starts self oscillating possible because of the
bad matching SMA/N connectors.
I have modified the old DB6NT once more and bridged the first pre-amp stage out
Original there was a NE225 then when this one broke replaced by SPF5043Z
The total gain plus the 36dB of SKY67151 was too high
There is not much remaining of the original DB6NT
Only mixer and 1.5W PA
The 1152 l.o chain was replaced by a TCXO 1150MHz DF9NP stand alone very stable!
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