13dka wrote: ↑Mon Sep 12, 2022 9:52 pm
I got the replacement SV1AFN preamp today (the first one lacked an inductor
) and gave it a brief indoor function test with the YouLoop.
First off, as expected it does
not work with 5V so I'd have to rethink my preamp power supply for portable operation. With 12V it seems to have the nominal 20dB of gain but with what looks like a noticeable gradual gain increase with frequency and what looks like no gain at all on
This is strange, see, the GALI-84+ declares an operating range (and gain) from DC to 6 GHz, and the SV1AFN web site says that that preamp works
from LF up to 4GHz; did you try mailing SV1AFN and asking some clarification ? as for the 12V, the
GALI datasheet states that the IC operating voltage is around 6V, but if you then look at the
SV1AFN schematic
.
- 29-11-2019-16-25-5de1468186347.jpg (83.78 KiB) Viewed 18777 times
.
we can clearly see that the preamp wants 12V, this is probably due to R1/R2 which are dropping the voltage (the power comes from the Bias-T formed by C2/L2); also, looking at the circuit, the frequency range limit is most probably set by C1/C2 and L1/L2, but then given that SV1AFN states that the unit works from LF, the fact that it has very little gain down on MW seems strange
A lot more gain down there. Since I had 12V available on the desk I decided to check for the first time what the LANA HF does with 12V. The short LANA HF manual states that it's supposed to work with 12V, even though "extended" operation with 12V is not recommended. I didn't intend to use it with 12V but I honestly expected it to survive more than 10 seconds, which it didn't. I attached the power supply to the Bonito CPI1000 bias-T unit, the LANA came on but with very little gain, I disconnected the power, checked the connections and plugged the 12V back in, it came on again and then the LED on the LANA went out.
Never tried the LANA-HF with 12V, the NooElec infos on site say that the preamp
may survive for a very short time to a 12V supply, but they warn that it may be quickly damaged, and ... well, you demonstrated it
! My wild guess is that while the IC used may accept 12V, the passive components (resistors/capacitors) surrounding it aren't rated for that voltage <sigh>
Of course I have yet to test the SV1AFN properly at the dike, particularly because the "visual" gain does not say much about the actual reception but it could turn out to be of somewhat limited use for the SULA this way. It also gets pretty warm and I'm afraid that means it will drain the battery a lot faster than the LANA HF. The LANA HF might be a bit sensitive (the other one died after A/B switching SULA and reference antenna a few times) and I guess I have to bite the bullet and order the W7IUV 2N5109 preamp or the 2SC5551 equipped model too, which burns up battery for the relays we don't really need for RX-only operation. The 2SC5551 model seems to have a particularly low noise figure which is certainly interesting.
if the gain is so low down at MW, I've little hope the SV1AFN will be so useful for the SULA, on the other hand, I believe that asking SV1AFN some clarification about the low gain may be due
At this point, it remains to see which preamp may be suitable for the SULA, the LANA-HF isn't bad since it demonstrated to work and since it's widely available, but having more choices would be nice, I was looking at
some preamps which look interesting, but they aren't commercial ones, and even if some of them may be available through various sources, they aren't easily found as the NooElec <sigh>
already modeled it as a circular loop, if you want I can post the NEC model, it will offer a slight more gain, but other than that, no advantage over the "diamond" version, again, for a first build, I'd start "by the book" also since the cross support can be built to be easily foldable, so allowing to carry the SULA around 
