Building a new receiver, this is going in a prime location - Suggestions for receiver/preamp/filter please

Cavity filters are not so great filtering wise. They are unique qualified for transmitting large amounts of power (emitting antenna) but for receiving are as good as cheaper SAW filters.

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He has the cavity filter in front of the amplifier on the prostick plus.
In that position the lower loss at the pass frequency is very beneficial compared to a SAW filter. (Or is the insertion loss similar? Don’t think so)

Edit: As you see in the post below, the cavity filter has only 0.5 dB of insertion loss. SAW filters have more around 2 dB insertion loss (COMPARISON OF 2 VERY SIMILAR 1090 Mhz SAW FILTER CHIPS)

I am using a Jetvision 3 pole cavity.

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Preamplifier raises the signal in the first stage and that more than compensate for any losses. The first stage won’t overload, unless you are right next to an emitter antenna.
The first stage noise factor is the one that will govern all chain.

LawrenceHill who brought up the cavity filter has no amplifier except the prostick plus internal one. The cavity filter sits between the antenna and Prostick Plus.
And i’ve read often enough that the prostick plus needs a filter in front of it for decent performance, so it seems to overload more often than you might think.

Anyway instead of spending 90 Euros for a cavity filter i would just get the rtl-sdr blog LNA together with the v3 dongle and be done with it.
(And buy an additional bias-t injector if one doesn’t want to fiddle around with the software bias-t, the guide is quite good though)

That’s my take. Cavity filters are expensive and not really necessary in our application (low power).
Even when I was using the FA Pro filter, with FA filter in front of it, no preamplifier, I was still lowering the gain to 38dB from the 45dB with the FA antenna… So the insertion loss wasn’t an issue for the stick with preamp.
I did try also the Pro Plus dongle that has the filter, but it wasn’t that much better than the other combo.

For most installations, I would agree with you.
I think I have much higher strength nearby signals than are normal.
I have experimented with a rtl-sdr blog LNA but the problem I had with it was one of heat.
During the summer when I was experimenting with things, the temperature in the loft was about 45C and the amplifier was at about 65C. The heat transfer to the dongle was causing it to also get excessively hot and it started to drop out. Hence I decided to go for a passive solution.

Well you could also use a pigtail between dongle and LNA to eliminate that heat transfer.
Small adhesive heatsinks are also relatively cheap if you want to passively cool the dongle or the Raspberry Pi.
But yeah the dongle and the LNA can get pretty hot. (Good that you remind me i’ll get some heat spreaders for the summer)

The heat was the reason why I opted to install only the preamplifier (with two SAW) out at the antenna and extend a long coax cable indoors. This way the dongle and receiver are protected from temperature extremes. The dongle DAC capabilities are affected by high temperature. The heat sinks won’t work so well inside a hermetically sealed ABS enclosure, they will just add heat to the air inside. Especially in the summer, I imagine will be a heat trap.

Thanks for the post Lawrence - that should help out a lot to compare long term trends (do remember the days to see if you had taken the top spot again :grinning: )

I have also just fired up the v3 again running alongside the airspy using splitter combo again, (so same antenna, LNA’s etc to splitter then separate same length feeds to both units) to see how the v3 fairs now.

airspy site 37839 - v3 site 90885 :+1:t2:

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hello navzptc. i have the same basic setup. i just started the mini on monday. i ran yesterday with the splitter and compared the v3 to the mini but when i changed the sampling rate to 20 my MLAT quit working . so today i am running with the mini and no splitter…tomorrow i will reinstall the splitter and stay with a sample rate of 12.
for 11 hours yesterday (with splitter but prior to trying m=20) i saw no basic change in aircraft counts but a 3.3% improvement in positions favoring the mini. i have lots of tuning to do and wiedehopf has been very helpful (and patient). i see that you just started the v3. i will be interested in your results

What gain are you using on both devices?

49.6 on v3 & 18 on airspy - both values I find best on them for my set up.

what length and type of cable between the lna and splitter?

I use CLF200 as its thin and easy to use/fit sma connectors to - I have about 5m to first lna, then 10m to second lna (when splitter in use) and splitter.

Well i guess the picture in my mind was very wrong. Thanks for that information.

On those settings do local flights cut out when they get too close?

I have a local heli/fixed wing airfield just over a mile away and am under a main route for heavy a/c and dont really suffer - can see fixed wing doing bumps & circuits etc.

Yes, it will be interesting to see how close in performance my site and your v3 are now.
I’ll have to see if I can manage to beat your B site :slight_smile:
The amount of traffic has dropped dramatically over the winter and I did wonder a while ago if there was something wrong, so I looked at your site and saw your numbers had dropped by what seemed to be about the same proportion; so I don’t think I’ve broken anything.

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i make your cable loss to be about 5dB. i am using LMR400 but have about 32m of cable from my lna to the splitter. so my loss is about 4dB but i have a lightening arrestor (loss of 0.4dB) and an external minicircuits bias-t (loss of .35dB) so we have similar loss but i only use one lna (rtlsdr lna 1090) with a gain of 27dB.
when i use the splitter the gain on the v3 was -10 and the gain on the mini was 21. when i removed the splitter (theoretical loss of 3.6dB/side) i dropped the mini to g=20.
what are the gains of your two lna’s?

Site states they have 14/15 db’ish gain on them (haven’t checked!) but fits with my findings.

As I mentioned, I found the loss through my mini circuits splitter to be 5.4/5.5 db (tracking SA used) so overall extra gain with 2nd lna 9’ish db - hence my drop from 21 (1 lna) to 18 (2 lna) 9db drop on airspy.