AM Broadcast Stations on 22 MHz

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Mike2459
Posts: 318
Joined: Mon Jul 24, 2017 8:24 pm

Re: AM Broadcast Stations on 22 MHz

Post by Mike2459 » Thu Jul 18, 2019 3:23 am

Amazon sells them for 16.95USD, but the 3db frequency is 2.5MhZ which would attenuate 160 Meter band, they have SMA connectors.

https://www.amazon.com/Broadcast-Reject ... B01N9SHS7P

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VK3MHZ
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Re: AM Broadcast Stations on 22 MHz

Post by VK3MHZ » Thu Jul 18, 2019 6:22 am

Mike2459 wrote:Amazon sells them for 16.95USD, but the 3db frequency is 2.5MhZ which would attenuate 160 Meter band, they have SMA connectors.
Thanks, so I am guessing with this I would not use the HiZ port and just into the SMA Ports on the RSP? Obviously I would need to get a balun for the long-wire then.

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Tech_Support
Posts: 499
Joined: Mon Jun 01, 2015 7:00 pm

Re: AM Broadcast Stations on 22 MHz

Post by Tech_Support » Thu Jul 18, 2019 8:48 am

I have an RSP2, which I brought about a year or two ago, can't recall precisely right now. Re MW on 22MHz, it was purely operator error, I had the receiver in Zero IF mode, once I click Low IF all was good.

Since you are tech support, you may be able to answer a question that has eluded me ever since I got it:

I have read posts stating there should be no difference in reception between using LIF and ZIF - this (at least in my case) is simply not true. Listening around 9 MHz to a station, in ZIF mode, reception was fine, switching to LIF the signal completely disappeared. Correct me if I am wrong, but I believe what I was hearing in ZIF mode was actually an AM broadcast image?

I just tried the above on 11 MHz just now, again in ZIF a rather strong signal, which I believe may have been ABC National here (AM BC), once I switched to LIF the signal was no longer present

Yet on all the framed bands (presets) everything is ZIF mode.
For normal tuning through bands, should I be using LIF or ZIF, or when is one to be used over the other?

OK, to be clear, there can be different mechanisms for spurious signals, depending upon what port you are using. All RSPs use a block converter to cover from 1kHz to 60 MHz. The block converter forms part of a dual conversion architecture and such an architecture will generate higher order spurious mixing products. Separately, there is also the issue of intermodulation, but that is a completely different mechanism from higher order mixing products.

The difference is explained in the following white paper that we published some time ago:

https://www.sdrplay.com/docs/SDRplay_Op ... _MW_HF.pdf

This paper also proposes some mitigation strategies depending upon which mechanism is creating the spurious response.

On the RSP2, the Hi-Z port has the best IMD performance, but is 'Wide open', i.e. it has no pre-selection filtering or optional notches. It is therefore more vulnerable to higher order spurious mixing products than ports A or B. However, higher order spurious mixing products are easy to identify and mitigate. If when you move the LO frequency, the actual frequency of the 'signal' changes, then it is a higher order spurious mixing product. Changing from LIF to ZIF or vice-versa changes the frequency plan and so changes where these spurs appear. In other words, you can move them 'out of the way' so that you can copy the real signal of interest.

With spurs that arise from IMD, you cannot play such tricks. Here, the only solution is to attenuate the input signal and/or apply additional external filtering.

Sincerely

Tech_Support

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Mike2459
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Re: AM Broadcast Stations on 22 MHz

Post by Mike2459 » Fri Jul 19, 2019 1:15 am

Here in the US Par Electronics sells them. They also will make custom filters according to their website. I don't own any of their products.

http://www.parelectronics.com/index.php

and DX Engineering
https://www.dxengineering.com/parts/hiz-hpf
75ohm connectors for Hi-Z antennas



Try a google search "HF bandpass filters for sale" or something similar for more

Mike

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VK3MHZ
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Re: AM Broadcast Stations on 22 MHz

Post by VK3MHZ » Sat Jul 20, 2019 3:17 am

Mike2459 wrote:Here in the US Par Electronics sells them. They also will make custom filters according to their website. I don't own any of their products.
Thanks again Mike I will take a look, appreciate your help. The ones I have seen so far also effectively knock out long wave bands to. I think maybe the best solution is to use the HiZ for MW & LW and then use a dipole (or whatever) in conjunction with a filter on Port A and put the VHF/UHF Antenna on Port B.

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Mike2459
Posts: 318
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Re: AM Broadcast Stations on 22 MHz

Post by Mike2459 » Sat Jul 20, 2019 4:17 am

That should work. I had problems on longwave with out of band HF and MW signals. I built a 3 pole elliptic LP filter in an Altoids can for the HiZ port that cuts everything above 520Khz. Works great, virtually no OOB stuff, it also lowered the noise levels somewhat on LW.

Mike

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g1hbe
Posts: 494
Joined: Sat Jan 17, 2015 3:28 pm
Location: Cheshire, UK

Re: AM Broadcast Stations on 22 MHz

Post by g1hbe » Sat Jul 20, 2019 7:16 am

Mike2459 wrote:That should work. I had problems on longwave with out of band HF and MW signals. I built a 3 pole elliptic LP filter in an Altoids can for the HiZ port that cuts everything above 520Khz. Works great, virtually no OOB stuff, it also lowered the noise levels somewhat on LW.

Mike
I did the same and the results were excellent. As I like to listen to the sub 100kHz band, I built another LPF specifically for it and the noise level dropped by about 10dB and the images from MW disappeared. IIRC (I never make notes), mine is a two section Chebyshev. It's amazing what signals have been revealed now all the clutter is out of the way.

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Andy

VK3MHZ
Posts: 41
Joined: Sun Apr 30, 2017 7:24 am

Re: AM Broadcast Stations on 22 MHz

Post by VK3MHZ » Sat Jul 20, 2019 11:43 pm

g1hbe wrote:I did the same and the results were excellent. As I like to listen to the sub 100kHz band, I built another LPF specifically for it and the noise level dropped by about 10dB and the images from MW disappeared. IIRC (I never make notes), mine is a two section Chebyshev. It's amazing what signals have been revealed now all the clutter is out of the way.
Andy;
Thanks for the info, sadly my building skills are hampered due to various reasons. So my only option is to buy. Being searching for a filter that will attenuate everything above 520 KHz. Our AM band starts at 531k here, and there are NDB's on 499, thus wanting to go a bit higher than most before attenuation kicks in.

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