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On Sun, Jul 12, 2020 at 06:36:17AM -0700, OneOfEleven wrote: Here's one of those little super dooper pre-amps that you can buy three for just 8 UK pounds (SPF5189Z 0.5dB-N.F 22dBm 1dB-Comp 50MHz to a few GHZ). They work wonderfully without any matching down below 30MHz up to GHz's, but I guess it helps to optimise things. That looks fantastic... will it also work down to 40m and 80m? if no, is there a similar preamp out there that will handle the lower bands?
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Does your receiver need a pre-amp? If the atmospheric/background noise INCREASES when you connect your antenna, you don't need a pre-amp with that antenna. Be sure to turn up the RF and AF gain enough so you can hear the radio's self noise before connecting your antenna. The atmospheric noise from your antenna will change between bands and with the season (thunder storms in summer create extra noise). Adding a pre-amp when it isn't needed can cause overload and intermodulation issues.
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Trouble is, these pre-amps have a LOT of gain once you get as low as 50MHz, mine has an attenuator on it because of that, and it's only stage of amplification in the entire receiver system, which is RF from the antenna, through the pre-amp and filtering then straight into a 16-bit ADC running at 125MHz (FPGA SDR).
I would not use a pre-amp on HF with todays radios.
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Especially on the low bands a preamp is not useful unless you are using a beverage or small loop for RX. With normal antennas just the opposite, adding some attenuation, is often helpful. 73 -Jim NU0C On Sun, 12 Jul 2020 13:35:43 -0700 david.hostetler@... wrote: Does your receiver need a pre-amp? If the atmospheric/background noise INCREASES when you connect your antenna, you don't need a pre-amp with that antenna. Be sure to turn up the RF and AF gain enough so you can hear the radio's self noise before connecting your antenna. The atmospheric noise from your antenna will change between bands and with the season (thunder storms in summer create extra noise). Adding a pre-amp when it isn't needed can cause overload and intermodulation issues.
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Post purpose: Practical usage of device on HF
So what does "min frequency" specification tells about how it performs on HF?
( I am aware of RX sensitivity and attenuators ).
I am asking for technical guess, not for lawyer's cop-out " if you use it out of spec you are on your own ".
Specifically because early adaptation of well know hardware as SDR HF (!) RX was also specified to operate well out of HF range. And it worked.
I'll czech it out on 50 MHz band , and up , soon.
End of post
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While this microwave capable device is cheap for the performance, for HF useful devices are going to be uber cheap in comparison, with transistors going for pennies, rather than dollars.
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Up till now there are guys that did not answer your question.
I know about the noise on HF bands, I know about receiver specs, I know about receiving antennas. Please spare me.
Here is an amp that also seems OK in HF (I have not tried it):
Next one you can build yourself:
(I am using this one myself for I don't know how long, on 160 and 80)
And there is more to find.
73
Arie PA3A
Op 12-7-2020 om 22:03 schreef namerati@...:
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On Sun, Jul 12, 2020 at 06:36:17AM -0700, OneOfEleven wrote:
Here's one of those little super dooper pre-amps that you can buy three for just 8 UK pounds (SPF5189Z 0.5dB-N.F 22dBm 1dB-Comp 50MHz to a few GHZ). They work wonderfully without any matching down below 30MHz up to GHz's, but I guess it helps to optimise things. That looks fantastic... will it also work down to 40m and 80m? if no, is there a similar preamp out there that will handle the lower bands?
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On Mon, Jul 13, 2020 at 09:48:49AM +0200, Arie Kleingeld PA3A wrote: Up till now there are guys that did not answer your question.
I know about the noise on HF bands, I know about receiver specs, I know about receiving antennas. Please spare me. You took the words right out of my mouth :) Here is an amp that also seems OK in HF (I have not tried it):
Next one you can build yourself:
(I am using this one myself for I don't know how long, on 160 and 80)
And there is more to find. Thank you!
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If you don't mind a bit of home brewing; Mini Circuits has lots of surface mount pre-amps dirt cheap (<$3), such as:
The only thing to watch is their overload performance. This one, in particular, is DC to 1 GHz, so you may want to add some frequency selectivity for that reason.
Stay well,
Brent
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A preamp is often needed on low noise receiving only antennas for 160 and 80 since they are negative gain antennas with excellent SNR and directional performance.
The Waller Flag, for instance needs about 40-45 dB gain.
Carl
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On 07/12/2020 5:27 PM OneOfEleven <cmoss296@...> wrote:
Trouble is, these pre-amps have a LOT of gain once you get as low as 50MHz, mine has an attenuator on it because of that, and it's only stage of amplification in the entire receiver system, which is RF from the antenna, through the pre-amp and filtering then straight into a 16-bit ADC running at 125MHz (FPGA SDR).
I would not use a pre-amp on HF with todays radios.
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On 8/5/20 2:23 PM, CARL HUETHER wrote: A preamp is often needed on low noise receiving only antennas for 160 and 80 since they are negative gain antennas with excellent SNR and directional performance.
The Waller Flag, for instance needs about 40-45 dB gain.
Carl
On 07/12/2020 5:27 PM OneOfEleven <cmoss296@...> wrote:
Trouble is, these pre-amps have a LOT of gain once you get as low as 50MHz, mine has an attenuator on it because of that, and it's only stage of amplification in the entire receiver system, which is RF from the antenna, through the pre-amp and filtering then straight into a 16-bit ADC running at 125MHz (FPGA SDR).
I would not use a pre-amp on HF with todays radios.
The OPA656 is a nice low noise operational amplifier to make a low noise preamplifier for lower frequencies. It will be hard to beat, except with a discrete JFET design such as that from Jefferts The nice thing about the op amp is that it can have fairly decent high level signal handling. Both of these can make a MF-HF LNA with a noise that's less than the galactic background for a short antenna (which is quite bright at 5MHz, if it weren't blocked by the ionosphere)
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I prefer a preamp that has some LC selectivity as well as a gain control for ham band use. Untuned preamps are fine ahead of instruments that need them.
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On 08/05/2020 6:52 PM Jim Lux <jimlux@...> wrote:
On 8/5/20 2:23 PM, CARL HUETHER wrote:
A preamp is often needed on low noise receiving only antennas for 160 and 80 since they are negative gain antennas with excellent SNR and directional performance.
The Waller Flag, for instance needs about 40-45 dB gain.
Carl
On 07/12/2020 5:27 PM OneOfEleven <cmoss296@...> wrote:
Trouble is, these pre-amps have a LOT of gain once you get as low as 50MHz, mine has an attenuator on it because of that, and it's only stage of amplification in the entire receiver system, which is RF from the antenna, through the pre-amp and filtering then straight into a 16-bit ADC running at 125MHz (FPGA SDR).
I would not use a pre-amp on HF with todays radios.
The OPA656 is a nice low noise operational amplifier to make a low noise
preamplifier for lower frequencies. It will be hard to beat, except
with a discrete JFET design such as that from Jefferts
The nice thing about the op amp is that it can have fairly decent high
level signal handling.
Both of these can make a MF-HF LNA with a noise that's less than the
galactic background for a short antenna (which is quite bright at 5MHz,
if it weren't blocked by the ionosphere)
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I use the preamp treated in the following reference for my shielded 0.75
and 2-meter loops:
Nominal gain of 25 dB with no intermod problems from 500 Hz through 30 MHz,
ever with some very strong AM broadcasters. Gain flatness across that
frequency range is 2 dB. I wound the output transformer on a low-frequency
ferrite in non-twisted bifilar manner.
I have tried a number of MMIC's for the purpose. None do as well as the
reference schematic and comments.
Concerning E-Field probes: With a JFET input (J-310) followed by an
emitter follower (2N5109), I have intermod problems with strong AM
broadcast stations.
Personally, the shielded loops make absolutely wonderful receive antennas
for ELF through HF. However, remember, the shielded loops are differential
sources, so a 'balun' or transformer is needed to feed coaxial cable.
Ideally, they would be fed directly with TSP (CAT 5 or CAT 6 cable)
followed by a differential discrete input amplifier (op amps are, again,
prone to intermod under strong signal conditions).
Dave - W?LEV
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On Thu, Aug 6, 2020 at 6:29 PM CARL HUETHER <k1uhy@...> wrote: I prefer a preamp that has some LC selectivity as well as a gain control
for ham band use. Untuned preamps are fine ahead of instruments that need
them.
On 08/05/2020 6:52 PM Jim Lux <jimlux@...> wrote:
On 8/5/20 2:23 PM, CARL HUETHER wrote:
A preamp is often needed on low noise receiving only antennas for 160 and 80 since they are negative gain antennas with excellent SNR and
directional performance.
The Waller Flag, for instance needs about 40-45 dB gain.
Carl
On 07/12/2020 5:27 PM OneOfEleven <cmoss296@...> wrote:
Trouble is, these pre-amps have a LOT of gain once you get as low as
50MHz, mine has an attenuator on it because of that, and it's only stage of
amplification in the entire receiver system, which is RF from the antenna,
through the pre-amp and filtering then straight into a 16-bit ADC running
at 125MHz (FPGA SDR).
I would not use a pre-amp on HF with todays radios.
The OPA656 is a nice low noise operational amplifier to make a low noise
preamplifier for lower frequencies. It will be hard to beat, except
with a discrete JFET design such as that from Jefferts
The nice thing about the op amp is that it can have fairly decent high
level signal handling.
Both of these can make a MF-HF LNA with a noise that's less than the
galactic background for a short antenna (which is quite bright at 5MHz,
if it weren't blocked by the ionosphere)
--
*Dave - W?LEV*
*Just Let Darwin Work*
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vaclav_sal:
These MMIC amps are often "just" a Darlington pair (two transistors), surrounded by up to a hundred other parts mostly concerned with maintaining DC bias levels. The low frequency response is limited by the LF cutoff of the bias network. MMICs exist that operate correctly down to DC, but they have quite different internal bias circuits that rely on matching tempco and other things, rather than RC low-pass filtering that always dictate some LF cut-off frequency.
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On 8/6/20 4:54 PM, Clifford Heath wrote: vaclav_sal:
These MMIC amps are often "just" a Darlington pair (two transistors), surrounded by up to a hundred other parts mostly concerned with maintaining DC bias levels. The low frequency response is limited by the LF cutoff of the bias network. MMICs exist that operate correctly down to DC, but they have quite different internal bias circuits that rely on matching tempco and other things, rather than RC low-pass filtering that always dictate some LF cut-off frequency.
- One problem, too, is that the 1/f knee for those GaAs or InGaP MMICs can be at a fairly high frequency (10s or 100s of kHz). You typically won't find that in the mfr data sheet. The parts are cheap, though. Try it and see. Typically, 4-5 components needed, 3 capacitors, 2 resistors, and a DC supply. I don't know what its noise properties vs frequency at low frequencies are, but the Minicircuits GALI-6 is representative. It's not a particularly quiet part (4dB NF).
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Worth a look for 28MHz up are at Lots of useful info on there too.
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Jim Shorney
Arie Kleingeld PA3A
Brent DeWitt