Jamie

It depends...on how you will be using your BITX.? For CW only your speaker might be

good if its response peaks at around 700 Hz.? For SSB only you might like a speaker
that has a "communications passband" of between 200 and 3200 Hz.? Amateur radio
does not require full bandwidth high-fidelity sound.?

Almost any small speaker will work.? The acoustic characteristics of the speaker housing
is usually more important than the speaker specification.?

Audio amplifier IC's usually use some sort of push-pull or totem-pole output stage and
thus will match from 4 ohms upward to 100 ohms.? Audio output power is usually
dependent on speaker impedance.? Lower impedance works the audio amplifier harder
and delivers more audio output.? It helps to look up the datasheet specification for the
particular AF output device to see what it says is best for impedance match and for
maximum output at specific impedances.

Arv? K7HKL
_._

On Mon, Jun 4, 2018 at 10:24 AM Jamie Anderson <jamiea@...> wrote:

I ordered a kit a few weeks ago and think I will be receiving the board with the updated discreet audio amp.? Somewhere I thought I saw that a 32 ohm speaker would be the best fit for this amp, but can't find this post anymore.? What is the best impedance and what is the approximate power out??

I found a small mylar speaker at Mouser that is 150 - 20K, but only 1/5 of a watt, 32 ohms.? Another speaker I found is a bit larger at another vendor, but is 16 ohms.? it is? 2 inches, and handles 2 watts, 180-17K so should be a bit better if this power amp puts out a watt or so.?

I can't seem to find the speaker that looks best for this "on paper" yet, just wondering about the new audio amp's requirements.

This can't be good:-(

Joel
N6ALT

Arv:
I just got an explanation from Allison, which I will confirm later. I measured the spurs in CW which I thought was a side tone, but isn't. I need to retest with actual audio.

Howard

On 6/4/2018 12:21 PM, Arv Evans wrote:

Howard

I'm seeing about the same.

Arv
_._

On Mon, Jun 4, 2018 at 10:18 AM Howard Fidel <sonic1@...> wrote:

Arv:
When properly driven, I see the spurs almost at -60dB.

Howard
On 6/4/2018 11:37 AM, Arv Evans wrote:

The uBITX does actually work on 15M, 12M, and 10M (and yes it does work on 11M as

evidenced by the number of CB'ers who have purchased it).? Power output is much lower

on the higher bands, but is still enough to make QRP contacts.? Just do not try to increase

power output on upper bands by adding microphone gain.? Too much microphone audio

will cause spurs, distortion, and QRM.?

Arv? K7HKL
_._

On Sun, Jun 3, 2018 at 9:01 PM Jerry Gaffke via Groups.Io <jgaffke=[email protected]> wrote:

To keep the price down, I think hfsignals may as well continue to use the 45mhz filter.
Perhaps claim 80m through 17m, beyond that is experimental, disable 15m,12m, and 10m
in the stock firmware.? Different transistors for more consistent gain should be considered.


However, if we can instrument drive level into the mixers, sounds like we may be able to have
a clean signal on up to 30mhz.? ?Perhaps replace transistors to get consistent gain through the 45mhz IF
and the Q90 stage, then monitor the top of RV1 with a diode RF probe into a Nano analog pin.

Better yet, add another 10dB of gain after the mixers so the IRF510's show trouble (much more obvious)
long before the mixers do.? So maybe add an extra gain stage between Q90 and RV1,
existing rigs could easily patch this in with an MMIC.?


If we do decide to go to 70mhz and beyond for that first IF, there are viable filters available.

In this post:??/g/BITX20/message/33203
Farhan explains that the 45mhz filter must be narrow enough to reject signals 2 mhz away from center.

Here's the filters on Mouser that are between 70 and 90 mhz, and have a bandwidth of less than 4mhz:
? ??

The PX1002 from Murata looks good to me, center frequency of 86.85mhz.
25khz wide, 3dB insertion loss, over 60dB of rejection at 1mhz out,
datasheet shows how to use it in 50 ohm environment.
Not exactly cheap at $12 single unit, $6 if buying hundreds from Mouser.
The similar PX1004 at 82.2mhz is harder to get, especially in low quantities,
but might be preferred as it allows a lower vfo frequency.?

To operate at 30mhz with an 86.85mhz first IF, the vfo should be 86.85+30 = 116.85mhz.
The Si5351's internal vco is spec'd to a max of 900mhz, and our fractional output dividers can divide down
to a minimum of 8.0, so 900/8=112.5mhz max using the current si5351bx routines with the vco moved to 900mhz.
Hans, G0UPL, has found that the vco can be pressed to go much higher, beyond 1100mhz,
so we could just cheat on that, perhaps 935mhz for the vco giving 935/8 = 116.875mhz max.
I'd try that first.
The other possibility is to use the second Si5351 internal vco with fractional pll feedback and an
integer output divider on clk1, giving fine grained frequency control up to 200mhz (290mhz, according to Hans).
This second method would roughly double the size of the si5351bx routines, but that's not a major hit.
The other two si5351 outputs would continue to use the first vco, and be restricted to 112.5mhz max.

If using the equations of post?/g/BITX20/message/44278
the only needed change to the uBitx code outside the Si5351bx routines would be to change this
uint32_t? f45c? = 44995000;? ? ?// center of 45mhz filter
? to this:
uint32_t? f45c? = 86850000;? ? ?// center of 87mhz filter

The filter and 50 ohm matching networks could be on a very small PC board
glued to the back of the uBitx main board.
This daughterboard could include a new BiDi amp with appropriate transistors.
If the uBitx mixers are problematic at 86.85mhz, then perhaps a couple ADE-1's also,
replacing everything from T2 to T4 inclusive.? Parts cost of around $10 if building hundreds,
$15 bucks if adding the two ADE-1's.?

Then everybody will get fixated on making the uBitx work on 6 meters
and we get to do this all over again.

Jerry, KE7ER

?
On Sun, Jun 3, 2018 at 03:44 pm, ajparent1/KB1GMX wrote:

Its not a drop in.? The filter would likely be hard to find and costly or for a one off salvage from?
an old junker commercial radio.?

I think Kenwood radios used a 63mhz filter or maybe ICOM.? so lets do a thought
experiment on what needs to be done.

The filter would need to be matched and like data for it will require experimental testing.
The T30-2 toroids could be reused and rewould and the cap for the L-networks changed
as needed.? The entire string of 3904s [all 6 of them] in the 45mhz section would have
to be some thing like 2n2369, or better BFR106s.?

Then the firmware has to be revised as the first lo needs to be higher to start maybe
65mhz and go up from there.??

So yes it can be done.? I don't have such a part so thats ruled out.? So for a one off
maybe, doesn't help everyone though. and even if the filter was not too expensive?
thats a lot of SMT and through hole work plus a new firmware.? At the production
level it could add significant cost and interrupt the product flow as you have all the
material in place and likely paid for.

Right now the most feasible option is bandpass filters and switching.? Cost wise the
parts are cheap is SMT inductors are used.? The trick there is drop in and play no
manufacturing tuning.

Allison

I ordered a kit a few weeks ago and think I will be receiving the board with the updated discreet audio amp.? Somewhere I thought I saw that a 32 ohm speaker would be the best fit for this amp, but can't find this post anymore.? What is the best impedance and what is the approximate power out??

I found a small mylar speaker at Mouser that is 150 - 20K, but only 1/5 of a watt, 32 ohms.? Another speaker I found is a bit larger at another vendor, but is 16 ohms.? it is? 2 inches, and handles 2 watts, 180-17K so should be a bit better if this power amp puts out a watt or so.?

I can't seem to find the speaker that looks best for this "on paper" yet, just wondering about the new audio amp's requirements.

When the power starts to fall off you are still putting out 8 watts
with the 1000 hz tone?

tim ab0wr

On Mon, 4 Jun 2018 13:04:33 -0400
"Ralph Mowery" <rmowery42@...> wrote:

> Using a HP 8924c in the SA mode I do not seem to be seeing any of the
> spurs down to at least
> - 50 dbm.? That is by feeding in a 1000 hz tone to the mic input and
> adjusting the audio level to maximum output and cutting it back to
> where the power just falls off.
>
> However I do see the carrier (that is supposed to be suppressed) of
> about -5 to 0 dbm.? That is with the modifications and RD16HHF1
> outputs for a power of about 8 watts on 28 MHz.

This posting contains two questions:

I am building a homebrew version of ubitx (on PCB layout I created myself). PCB was manufactured a year ago, but did not start bringing up circuit at that time.

Since about 2 weeks ago, I have been bringing up the receive path first (along with necessary microcontroller and synthesizer stages), one stage at a time, beginning with the loudspeaker, and so far having good results and fun experience.

I realize now (that I am at the 45 MHz IF filter, heading towards the first mixer) that I did not save schematic I used to create PCB, and v3 schematic (more recent) includes a part (the 45 MHz crystal filter) I did not find in the version I based my PCB layout on. I understand the benefit of the filter, however, I wish to continue progress on my PCB based on older design, as I will gather changes (including use of the newer IF filter design) for a future PCB rev.

My PCB layout assumed multi-pole LC filter from the schematic I had available at the time (original or maybe v2, but not v3 or later). In this version, the 45M15(A? B? F?) filter was not included, and it is not present on my PCB layout.

So, I have two questions:

1. What is URL or other way to find version of ubitx based on LC filter in 45 MHz path?

2. Where is current source for the 45M15 (A? B? F?) filter used in V3 and later designs? I did not find it in search on US distributors nor on ebay; I understand these should be low cost part with good availability, so I think I am not looking in right place?

Thank you, and this is very enjoyable project!

73 Dave WB0GAZ wb0gaz@...