Jim, it has been a long time since I got to ask a question of a PhD
engineer type!
IF the transceiver had harmonics and those were transferred to the linear,
would they not be amplified by a factor of ten? (at least where the
harmonics fell into the range that the amp might be able to work on them)
Then, if they were filtered they might not be so quiet as to be
insignificant? A filter isn't a brick wall for those frequencies outside of
the pass band. If filtered before the amp, the linear amplification would
only be done on the good stuff, right? I would think the overall effect
would be a cleaner signal out of the linear, and a lower overall content of
harmonics to filter (only those generated by the linear amp (which would
mean it was not so linear)) .
I guess I am, for the sake of discussion, assuming the amp was being
driven by equipment inferior to TenTec, (or perhaps Elecraft to keep those
guys happy) with it's resulting rice-induced harmonic content. :) Please
ignore the dumb presentation, but I am seriously asking the question: Might
not there be benefit to filtering between the exciter and the linear
amplifier if the exciter was not clean?
--------------------------------------------------
From: "JAMES HANLON" <knjhanlon@msn.com>
Sent: Monday, May 19, 2008 1:55 PM
To: "Discussion of Ten-Tec Equipment" <tentec@contesting.com>
Subject: Re: [TenTec] Low Pass Filter
> Ed,
>
> A properly designed filter should be terminated in its characteristic
> impedance at your operating frequency, probably 50 ohms, and will present
> a 50 ohm impedance at its input at your operating frequency as well. So
> putting a filter in between the output of your transceiver and the input
> of your amplifier should not upset the load impedance for the transceiver
> as long as the amplifier input looks like 50 ohms as well.
>
> However, it is probably overkill to put a filter there. One filter at the
> output of the amplifier will sufficiently attenuate all of your harmonics
> and other unwanted signals above the filter cutoff frequency that leave
> via the amplifier output coax lead. Decent shielding of the transceiver
> and amplifier and proper filtering of the wires coming out of them, like
> power lines, microphone, key and headphone leads, etc, will keep any
> unwanted signals from getting out through open holes or on those wires.
> Just about all modern equipment has adequate shielding and filtering, so
> you normally shouldn't have any problems there. So one low pass filter in
> the coax at the amplifier output should be sufficient. Also, I see no
> technical reason for keeping the coax cable between the amplifier output
> and the filter short, other than the possibility that the shielding on
> that lead is less than perfect and that would allow an unwanted signal to
> leak out. As far as the impedance presented
> to the amplifier output, that won't be changed by the length of the cable
> to the filter as long as the filter works into a matched, usually 50 ohm
> load.
>
> Jim, W8KGI (PhD, EE)
> ----- Original Message -----
> From: Edward Sylvester<mailto:navydude1962@yahoo.com>
> To: Discussion of Ten-Tec Equipment<mailto:tentec@contesting.com>
> Sent: Sunday, May 18, 2008 11:41 AM
> Subject: Re: [TenTec] Low Pass Filter
>
>
> As for LPF, should I use two; one on the output of the linear and one on
> the output of the radio? Will double by RF supression or is this
> overkill??
>
> Ed NI6S
>
> JAMES HANLON <knjhanlon@msn.com<mailto:knjhanlon@msn.com>> wrote:
> There is an R. L. Drake Low Pass Filter on ebay, item 320251164898,
> ending at 12:58 PDT Sunday. Its current price is $8.28 with two bids. It
> should be a good one.
>
> There is also a Nye Viking filter, item 290230177453, ending Monday at
> 14:16 PDT. Its current price is $1.04 with two bids. It should also be
> good.
>
> There is another Drake filter, item 310050424821, ending at 19:00 on May
> 20. Its current price is $7.99 with no bids.
>
> There is a Drake TV-3300-LP, item 160241874048, ending at 07:53 on May
> 23. Its starting price is $5 with no bids.
>
> There is a Drake TV-3300-LP, item 2302522446865, ending at 14:20 on May
> 23. Its starting price is $9.99 with no bids.
>
> There is a Bencher YA-1, item 190222711105, ending May 25 at 18:30. Its
> current price is $9.99 with one bid.
>
> Any of these should be a good filter for a legal limit rig.
>
> Jim, W8KGI
>
> _______________________________________________
> TenTec mailing list
> TenTec@contesting.com<mailto:TenTec@contesting.com>
>
> http://lists.contesting.com/mailman/listinfo/tentec<http://lists.contesting.com/mailman/listinfo/tentec>
>
>
>
> _______________________________________________
> TenTec mailing list
> TenTec@contesting.com
> http://lists.contesting.com/mailman/listinfo/tentec
>
_______________________________________________
TenTec mailing list
TenTec@contesting.com
http://lists.contesting.com/mailman/listinfo/tentec
|