[Antennaware] Antennaware Digest, Vol 117, Issue 1
k8mp at aol.com
k8mp at aol.com
Tue Feb 5 16:18:01 EST 2019
Thanks Jay.
-----Original Message-----
From: Jay Terleski <jayt at arraysolutions.com>
To: k8mp <k8mp at aol.com>
Cc: wr5o <wr5o at icloud.com>; antennaware <antennaware at contesting.com>; Ward Silver <hwardsil at gmail.com>
Sent: Tue, Feb 5, 2019 01:57 PM
Subject: Re: [Antennaware] Antennaware Digest, Vol 117, Issue 1
There are other products.ARRL reviewed the Array Solutions RX-FEP front end protector and found it excellent.https://www.arraysolutions.com/as-rxfep
Try it out if it doesn't do the job send it back for a refund. No kidding. Jay, WX0B
Jay Terleski
Array Solutions
214 954 7140
On Tue, Feb 5, 2019 at 12:42 PM Joe via Antennaware <antennaware at contesting.com> wrote:
Thanks Brent
-----Original Message-----
From: Robert Scott <wr5o at icloud.com>
To: k8mp <k8mp at aol.com>
Cc: hwardsil <hwardsil at gmail.com>; antennaware <antennaware at contesting.com>
Sent: Tue, Feb 5, 2019 12:58 pm
Subject: Re: [Antennaware] Antennaware Digest, Vol 117, Issue 1
There are products to protect your receiver that are available from DX Engineering however,depending on your radio,it might have the option to switch between antennas automatically. The big issue is the passive coupling between the two. The transmit antenna is receiving noise and when coupled to the BOG will transfer this noise to it. That being said you need at least a wavelength of separation to avoid this. I know that is not possible in most situations including mine so I live with it. The benefits of the beverage are still good even in this situation. Here is my BOG on 160 last night. This beverage is approximately an eighth of a wavelength separated from my inverted L and lays across the street and into a neighbors yard when I have it deployed.
Brent Scott
WR5O
> On Feb 5, 2019, at 9:45 AM, Joe via Antennaware <antennaware at contesting.com> wrote:
>
> Hey Ward, et al,
> This is not related to the original topic but you mentioned BOG antennas and I have a question.Is installing a BOG near the ground system of an Inverted-L dangerous for a receiver? Separation between them would be about 1/8 wavelength, perhaps less, from the nearest radial.
> In my situation, there would be radials and the BOG(s) in the same body of water. I have no clue how much RF current and voltage would be in there.
> Thanks, Joe, K8MP
>
> -----Original Message-----
> From: Ward Silver <hwardsil at gmail.com>
> Cc: antennaware <antennaware at contesting.com>
> Sent: Tue, Feb 5, 2019 09:57 AM
> Subject: Re: [Antennaware] Antennaware Digest, Vol 117, Issue 1
>
>
> I would suggest that you contact K9AY directly about the impedance mismatch
> - k9ay at k9ay.com
>
> From my experience and in reviewing a lot of literature, unless the loop is
> *really* small, preamplifier noise figure is not significant on the lower
> HF and MF bands. I suppose it might be an issue for desktop rotatable
> loops or "Beverage on Ground".
>
> 73, Ward N0AX
>
> On Tue, Feb 5, 2019 at 5:43 AM Andrew Ikin <andrew.ikin at btopenworld.com>
> wrote:
>
>> Hello Ward,
>>
>> I think I need to rephrase my email. What I am trying to say is, a small
>> terminated antenna e.g. a Flag or a Waller Flag is noise limited by the
>> termination resistor. This is because the resistor has a 3dB noise figure.
>> The antenna loss or low radiation resistance doesn't matter so much as this
>> loss can be made up with an LNA. The issue is made worse because most
>> practical
>> designs have the matching transformer z that is the same as the termination
>> resistor. Now if we use amplifier with high input z of say 30k Ohms; using
>> chemandy.com Return loss and mismatch loss calculator
>> the resistor noise is miss-matched to the amp. by approx. 10dB.
>>
>> Thus the antenna noise floor should be lower. However, I am assuming that
>> the LNA has negligible noise when terminated with the antenna. This could
>> be
>> a design issue to get the noise figure down to less that 0.5dB!!!
>>
>> The example I gave using a high z amp. with the K9AY suggests that there is
>> no loss in gain by using increasing the input z.
>>
>> 73
>>
>> Andrew G8LUG
>>
>> -----Original Message-----
>> From: Ward Silver
>> Sent: Monday, February 4, 2019 7:50 PM
>> To: antennaware at contesting.com
>> Subject: Re: [Antennaware] Antennaware Digest, Vol 117, Issue 1
>>
>> A flux-coupled transformer with separate windings provides galvanic
>> isolation between the feed line shield's outer surface and the loop.
>> Coupling from the loop to the feed line can upset the pattern and couple
>> noise on the feed line into the antenna.
>>
>> It is also a good idea to add a choke of several thousand ohms on the feed
>> line at the antenna to prevent common-mode current on the outside of the
>> feed line shield from getting into the cable and becoming differential-mode
>> signals. Same concern at the receiving end although most receivers are
>> well-shielded.
>>
>> 73, Ward N0AX
>>
>> On Mon, Feb 4, 2019 at 11:00 AM <antennaware-request at contesting.com>
>> wrote:
>>
>>> Send Antennaware mailing list submissions to
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>>> Today's Topics:
>>>
>>> 1. Fw: source impedance of resistor terminated antennas (Andrew Ikin)
>>>
>>>
>>> ----------------------------------------------------------------------
>>>
>>> Message: 1
>>> Date: Sun, 3 Feb 2019 23:04:32 -0000
>>> From: "Andrew Ikin" <andrew.ikin at btopenworld.com>
>>> To: <antennaware at contesting.com>
>>> Subject: [Antennaware] Fw: source impedance of resistor terminated
>>> antennas
>>> Message-ID: <2E4939776E6344ECB4242B584629630C at DESKTOPCPQEP29>
>>> Content-Type: text/plain; charset="UTF-8"
>>>
>>>
>>>
>>> From: Andrew Ikin
>>> Sent: Sunday, February 3, 2019 10:38 PM
>>> To: antennaware at contesting.com
>>> Subject: source impedance of resistor terminated antennas
>>>
>>> Is there any reason why most resistor terminated antennas like the K9AY
>>> and the Flag use a matching transformer to the Rx feed line that has the
>>> same impedance as the termination resistance. The reason for the question
>>> is, such antennas have a ideal match to the 3dB noise generated by the
>>> termination resistor and this resistor has no radiation resistance.
>> Hence,
>>> for antennas like a small size Flag, the performance could be limited by
>>> the resistor noise.
>>>
>>> However, if the antenna is connected to a high zin amp., then the
>> resistor
>>> noise should be reduced by the miss-match and if the amp. noise figure is
>>> very low, then it may be possible improve the antenna performance?
>>>
>>> Winding the clock back 20 years I noticed that the K9AY Rx matching
>>> transformer could be replaced by a high zin amp. with a voltage gain of
>>> 11dB. The overall gain increase compared to using 9:1 z transformer was
>>> 20dB. This increase in gain is what would be expected (11dB amp. plus 9dB
>>> by replacing the 9:1 transformer). Thus, the antenna gain compared to one
>>> without the amp. had not been degraded by using high zin amp.. However,
>>> then I didn?t consider the effect of resistor noise, but this wouldn?t be
>>> an issue with the K9AY.
>>>
>>> Is there something else I need to consider?
>>>
>>> 73
>>>
>>> Andrew Ikin
>>> G8LUG
>>>
>>> ------------------------------
>>>
>>> Subject: Digest Footer
>>>
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>>> ------------------------------
>>>
>>> End of Antennaware Digest, Vol 117, Issue 1
>>> *******************************************
>>>
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